Subject: What's this? From: Jack Ivey ivey@.......... Date: Wed, 31 Mar 2004 18:01:03 -0500 Hi all, Does anyone know what a model SD-217 from Teledyne Earth Science is? 5" dia X 8" high. Thanks, Jack __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: harmonics From: "tdick" dickthomas01@............. Date: Thu, 1 Apr 2004 08:51:51 -0600 What is the best way to remove harmonics in Lehman without changing the period? __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: harmonics From: "Connie and Jim Lehman" lehmancj@........... Date: Thu, 1 Apr 2004 10:21:32 -0500 Dick--I'm at a loss to know exactly what "harmonics" you speak of??? I know this is April 1----Are you speaking of the natural period of the pendulum??? More info please-- Have a great day! Jim Lehman ----- Original Message ----- From: "tdick" To: Sent: Thursday, April 01, 2004 9:51 AM Subject: harmonics > What is the best way to remove harmonics in Lehman without changing the > period? > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: harmonics From: "tdick" dickthomas01@............. Date: Thu, 1 Apr 2004 09:21:16 -0600 No -- not April Fool's thing -- have setup Lehmans with longer period but have harmonics > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: harmonics From: Jack Ivey ivey@.......... Date: Thu, 1 Apr 2004 11:54:29 -0500 Nope, still don't know what you mean. Do you mean unwanted vibrational modes and/or cross-axis sensitivity, i.e. your horizontal boom has a 15 s period, but it also bounces vertically at 0.5 s period? What's the symptom? Jack -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of tdick Sent: Thursday, April 01, 2004 10:21 AM To: psn-l@.............. Subject: Re: harmonics No -- not April Fool's thing -- have setup Lehmans with longer period but have harmonics > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Analog Design Tools From: Karl Cunningham karlc@.......... Date: Fri, 02 Apr 2004 15:57:45 -0800 If you're doing analog design (amplifiers, filters, etc.) you might want to check out Texas Instruments' analog design tools on their web site... http://www.ti.com/amplifier_utilities Especially the program to build 1% resistor values from paralleling 5% components, and FilterPro is VERY good. Regards, Karl Cunningham __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Simple mini horizontal From: "Ted Rogers" tedr@.................. Date: Thu, 8 Apr 2004 08:52:05 +1000 Hi John has kindly posted my attempt at a 'mini horizontal' seismograph, if you are interested please go to: http://jclahr.com/science/psn/rogers/ I would be grateful for an comments or improvements you may think I might incorporate in the unit, especially in the area of feed back to the light source. Regards Ted Rogers __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Simple mini horizontal From: "Steve Hammond" shammon1@............. Date: Wed, 7 Apr 2004 16:48:30 -0700 Ted, I took a quick look, that does not look simple to me... Looks neat-- Steve Hammond PSN San Jose Aptos, CA -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Ted Rogers Sent: Wednesday, April 07, 2004 3:52 PM To: psn-l@.............. Cc: John Lahr Subject: Re: Simple mini horizontal Hi John has kindly posted my attempt at a 'mini horizontal' seismograph, if you are interested please go to: http://jclahr.com/science/psn/rogers/ I would be grateful for an comments or improvements you may think I might incorporate in the unit, especially in the area of feed back to the light source. Regards Ted Rogers __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Simple mini horizontal From: "David H. Youden" dyouden@............. Date: Thu, 08 Apr 2004 11:06:24 -0400 Ted, I took a look at John's website and I think that you did a nice job. I like it. I am fooling with using a 500 second integrator for leveling bias. The output of the integrator is applied to the motor at the summing junction of the PID feedback loop. It seems to work OK but I may just bite the bullet and add a second motor dedicated to simply providing the position bias. I hate to add the extra wire, so I will test the existing system for a bit before I give up on it. Dave Youden > > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Simple mini horizontal From: "Ted Rogers" tedr@.................. Date: Fri, 9 Apr 2004 19:05:26 +1000 David Tanks for the complement, I know it's not really a 'simple mini horizontal' but it was inspired by John Lahr's model as seen on his web site. The reason I though about using the light source in the sensor assembly to overcome tilting was to over come the use of motors etc. to remotely level the unit. As I am using a tapered 'flag' and tilt either due to temperature or ground movement would alter the amount of light reaching the phototransistor. Having set a stable sensor output level and a reference voltage equal to it, the idea was that any (very) slow change in output level would be compared to the reference voltage and the light source adjusted to compensate, I did suggest 1 minute integration but about 10 minutes would seem to be a better figure. Regards Ted Rogers > Ted, > > I took a look at John's website and I think that you did a nice job. I > like it. > > I am fooling with using a 500 second integrator for leveling bias. The > output of the integrator is applied to the motor at the summing junction > of the PID feedback loop. It seems to work OK but I may just bite the > bullet and add a second motor dedicated to simply providing the position > bias. I hate to add the extra wire, so I will test the existing system > for a bit before I give up on it. > > Dave Youden > > > > > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Software for Radio Shack DI-150RS From: "Dewayne Hill" n0ssy@........... Date: Sat, 10 Apr 2004 10:59:24 -0600 I had to format my hard drive. I lost my software for my DR-150RS. If anyone has a copy can you send it to me? Dewayne Hill - n0ssy N39 50.139 W105 3.748
I had to format my hard drive. I lost my software for my = DR-150RS.
 
If anyone has a copy can you send it to me?

Dewayne Hill - n0ssy
N39 50.139
W105 = 3.748
Subject: Fwd: SPRENGNETHER 5000 HORIZONAL LONG PERIOD SEISMOMETER From: "Larry Cochrane" lcochrane@.............. Date: Sat, 10 Apr 2004 22:43:38 -0700 Hi everyone, I was asked by Jim Allen to forward the following message to the list. He uses AOL so he's not on the PSN-L list any more. -Larry I just received a Spregnether 5000 long period horizontal seismometer similar to the ones on Meredith Lamb's website. However, it is missing the lower far rear piece that clamps the pivot wire. Its the piece that floats just ahead of the frame (approximately 2+ inches long). If anyone has parts or know a source for parts for this unit I would appreciate hearing from them so I can get the unit working. If anyone can help, please respond directly to my email: radiotel@....... __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Software for Radio Shack DI-150RS From: Stephen & Kathy skmort@.......... Date: Sat, 10 Apr 2004 22:47:12 -0700 Hi Dewayne,, I run a DI-150RS which I bought from Radio Shack some years ago! The program they sent with the unit did not work,,,, I had to download a program from the Dataq web site,,, (you now have to register to get to their support site,,, I haven't bothered to register yet,, so I don't know what their latest versions might be!) I am now running version 2.66 the downloaded program is named new100nt.exe it has both the record and playback programs as well as some samples and is about 2,106 kb! I also have a version 2.72 which I haven't tried yet,,, it is supposed to have event triggers,,, it is also called new100nt.exe and is about 2,877 kb During setup, it asks which dataq unit you have, so it will run several (but not all) dataq units??? Off hand I don't remember which ones they were???? If you think you would like to try them, I will be glad to burn either, or both on a CD and send them to you!! My email is skmort@.......... Stephen psn Station #55 38.828N 120.979W > Dewayne Hill wrote: > > I had to format my hard drive. I lost my software for my DR-150RS. > > If anyone has a copy can you send it to me? > > Dewayne Hill - n0ssy > N39 50.139 > W105 3.748 __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: OT for Stephen From: "Bob Shannon" earth@........... Date: Sun, 11 Apr 2004 02:17:45 -0700 -----Original Message----- Stephen; Have lost your email. Please send me a note to reply to. Bob Shannon Pinpoint From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Stephen & Kathy Sent: Saturday, April 10, 2004 10:47 PM To: psn-l@.............. Subject: Re: Software for Radio Shack DI-150RS __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Gorda Locked From: "Bob Shannon" earth@........... Date: Sun, 11 Apr 2004 07:10:21 -0700 I have been thinking about Gorda and its locked position for a long time now...but this AM I awoke with a question I don't believe I have ever asked....Is there any other scenario in the world, similar to Gorda where a small plate is locked and could break loose???? Bob Shannon __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Fwd: SPRENGNETHER 5000 HORIZONAL LONG PERIOD SEISMOMETER From: "Meredith Lamb" meredithlamb@............. Date: Sun, 11 Apr 2004 13:57:10 -0600 Hi Jim, Highly doubt a spare will be found due to the age of the instrument.....it was discontinued many years ago....even though it a very reliable and highly effective seismometer. I think its a piece one can either carefully homebrew or have a machine shop ($) make. I think the part can be made from 1/2" X 1/2" X ~1.75" length keystock iron found in hardware stores. Its sold as square rods about 1 foot long. "IF", you try this, I'd take along a file to make sure the keystock is metal workable (the iron can be filed); some keystock is heat treated and is so hardened it might not be workable. It doesn't have to be a exact match of the original to function. After drilling the wire hole; I'd install two setscrews on another opposite side, to hold the wire from moving. The boom "prong" holes are probably deep enough to where its about 2/3rds through the thickness for stability. With your boom prongs, you can measure their relative distance from the centered wire hole center. Making this part is probably the only alternative. Take care, Meredith > [Original Message] > From: Larry Cochrane > To: > Date: 4/10/2004 11:43:38 PM > Subject: Fwd: SPRENGNETHER 5000 HORIZONAL LONG PERIOD SEISMOMETER > > Hi everyone, > > I was asked by Jim Allen to forward the following message to the list. He > uses AOL so he's not on the PSN-L list any more. -Larry > > I just received a Spregnether 5000 long period horizontal seismometer > similar to the ones on Meredith Lamb's website. However, it is missing the > lower far rear piece that clamps the pivot wire. Its the piece that floats > just ahead of the frame (approximately 2+ inches long). If anyone has parts > or know a source for parts for this unit I would appreciate hearing from > them so I can get the unit working. > If anyone can help, please respond directly to my email: radiotel@....... __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Gorda Locked From: John Hernlund hernlund@............ Date: Sun, 11 Apr 2004 13:01:28 -0700 Yes, this is a common scenario in several subduction zones, where the largest earthquakes are generated. The Juan de Fuca and Gorda plates are a bit of an oddity though, since the ridge is so close to the trench, making the plate size and age smaller. The young age means the ocean lithosphere is thin and the whole thing is more buoyant than old oceanic lithosphere (it resists being pushed under). A similar plate scenario exists in southwestern Mexico (Oaxaca region) and parts of the west coast of South America (parts of the Japan subduction zone also get locked up and can generate giant EQs, although the age of subducting plate is different in the north and south). JdF and Gorda are dangerous, since the recurrence interval is so long compared to those in other places and if you are around for one, things might not be so good. Perhaps a more important measure is the recurrence interval times the plate convergence speed, which gives you the average length of convergence (offset) per earthquake, which in turn figures into the magnitude of the EQ that can be generated (offset times fault area times shear modulus). Another good practical measure is a person's average lifespan divided by the recurrence interval in the area they live in...which in the case of the Pac NW turns out to be nice and small compared to Oaxaca (which is probably the most dangerous of all when coupled with population, economic and engineering factors). A similar recurrence interval to the Pac NW exists for the giant thrust fault system that cuts across LA. Cheers! John On Sunday, April 11, 2004, at 07:10 AM, Bob Shannon wrote: > > > I have been thinking about Gorda and its locked position for a long > time > now...but this AM I awoke with a question I don't believe I have ever > asked....Is there any other scenario in the world, similar to Gorda > where a small plate is locked and could break loose???? > Bob Shannon > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Fwd: SPRENGNETHER 5000 HORIZONAL LONG PERIOD SEISMOMETER From: apsn apsn@........... Date: Sun, 11 Apr 2004 14:19:55 -0800 I might have what you need, Jim. I think I have parts for a Sprengnether 5000 vertical or horizontal, I cannot remember which. Give me some time to find them and see if they match what you're after. Bob http://apsn.awcable.com At 11:57 AM 4/11/2004, Meredith Lamb wrote: >Hi Jim, > >Highly doubt a spare will be found due to the age of the instrument.....it >was >discontinued many years ago....even though it a very reliable and highly >effective >seismometer. > >I think its a piece one can either carefully homebrew or have a machine >shop ($) >make. I think the part can be made from 1/2" X 1/2" X ~1.75" length >keystock iron >found in hardware stores. Its sold as square rods about 1 foot long. >"IF", you try this, >I'd take along a file to make sure the keystock is metal workable (the iron >can be filed); >some keystock is heat treated and is so hardened it might not be workable. >It doesn't >have to be a exact match of the original to function. After drilling the >wire hole; I'd >install two setscrews on another opposite side, to hold the wire from >moving. The >boom "prong" holes are probably deep enough to where its about 2/3rds >through the >thickness for stability. With your boom prongs, you can measure their >relative distance >from the centered wire hole center. Making this part is probably the only >alternative. > >Take care, Meredith > > > > [Original Message] > > From: Larry Cochrane > > To: > > Date: 4/10/2004 11:43:38 PM > > Subject: Fwd: SPRENGNETHER 5000 HORIZONAL LONG PERIOD SEISMOMETER > > > > Hi everyone, > > > > I was asked by Jim Allen to forward the following message to the list. He > > uses AOL so he's not on the PSN-L list any more. -Larry > > > > I just received a Spregnether 5000 long period horizontal seismometer > > similar to the ones on Meredith Lamb's website. However, it is missing >the > > lower far rear piece that clamps the pivot wire. Its the piece that >floats > > just ahead of the frame (approximately 2+ inches long). If anyone has >parts > > or know a source for parts for this unit I would appreciate hearing from > > them so I can get the unit working. > > If anyone can help, please respond directly to my email: radiotel@....... > > > >__________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email PSN-L-REQUEST@.............. with >the body of the message (first line only): unsubscribe >See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Quake scientist's conference From: "Erich Kern" efkern@............. Date: Wed, 14 Apr 2004 13:06:41 -0700 From: www.thedesertsun.com The Desert Sun / Palm Springs, California Forecast the buzz as quake scientists gather By Benjamin Spillman The Desert Sun April 14th, 2004 -------------------------------------------------------------- It's tough to fault seismologists for earthquakes that rocked the Los Angeles basin in 1994 and the Bay Area in 1989. But the group of researchers who in both years held conferences near those memorable temblors are now in Palm Springs -- and some are predicting a major quake along the desert's slice of the San Andreas. The expectation that the southern portion of the famous fault is likely to rupture is based on more than a scheduling quirk or the fact that this is Earthquake Preparedness Month. But the annual conference of the Seismological Society of America comes at a time when earthquake prediction is a hot topic in the field. The conference, described by an organizer as an event "for the real purists" of seismology, includes a highly anticipated forum with one forecaster who is predicting a 6.4 magnitude or greater quake in the desert by Sept. 5. Another researcher will present data he says indicates the San Andreas fault is set to enter a period of especially frequent and more intense shaking. "It seems perfect," said University of Oregon professor Ray Weldon of the conference location. "That is going to be about the center of the rupture if we are all right." Weldon will speak today at the event about data he and student researchers have spent 18 years gathering from the San Andreas fault near Wrightwood. They say data from the site shows the fault has had varying levels of stress in the past 1,500 years. Today, the fault shows high levels of stress, suggesting a period of strain release, via earthquakes, is near, he said. The research generally applies along the fault from about Palmdale to the Salton Sea. Although Weldon doesn't offer a quake prediction per se, he said the work complements a prediction by Russian scientist Vladimir Keilis-Borok, the UCLA researcher forecasting the 6.4 magnitude or greater quake in the desert. "You could consider that support," Weldon said. "But I don't lend any insight or support to a window of time." The Keilis-Borok earthquake prediction window has been a major topic of conversation among seismologists this year. Keilis-Borok and his team used a mathematical formula based on past seismic activity to predict a temblor somewhere in an approximately 12,000 square-mile swath of desert that includes the Coachella Valley. "Even two years back it was practically a dirty word to say earthquake prediction," said Nancy Sauer, a conference organizer. The buzz around predictions this year is reminiscent of earlier enthusiasm for earthquake forecasting in the late 1970s and early 1980s, said John McRaney, associate director of the Southern California Earthquake Center. But for the most part those efforts fizzled, McRaney said. "It was so unsuccessful . people sort of shied away for about 20 years," he said. Rich Eisner, manager of earthquake programs for the California Office of Emergency Services, recalls trekking to the tiny California town of Parkfield around 1988 in response to a high-profile earthquake prediction. Parkfield, population 37, was then known for its proximity to the site of the car accident that killed actor James Dean, Eisner said. However, when researchers predicted a major temblor would occur in the area within a three-day window, scientists and media flocked to the area, he said. "It became an opportunity to catch the earthquake," Eisner said. "Most of the time earthquakes occur and the instruments are in the wrong location." The quake never materialized, but Parkfield emerged with the self-proclaimed title "earthquake capital of the world" and the Office of Emergency Services still has an earthquake response plan it formed around the time of the old prediction. "From our standpoint, it was a productive and successful exercise," Eisner said. Now, with Keilis-Borok scheduled to speak Thursday afternoon, the one-time dirty word could be the highlight of the society's conference, an event they've held almost every year since 1907. "There is something going on," Sauer said. "People are at least willing to entertain the idea. It is not seen so much as junk science." Keilis-Borok isn't talking about his work right now because he wants it to appear in a journal that discourages researchers from speaking to the press before publication of a scientific article. The conference, which was scheduled more than a year before the desert quake prediction, represents a confluence of an opportunity to listen directly to Keilis-Borok at a location well within his prediction zone. "Everyone is talking about it," said Lisa Grant, a University of California, Irvine geologist who will attend the conference. "Earthquake prediction is the holy grail of earthquake science." -------------------------------------------------------------- Benjamin Spillman can be reached at 778-4643 © Gannett Co., Inc., 7950 Jones Branch Drive, McLean, VA 22107 . (703) 854-6000 Copyright © 2004 The Desert Sun. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: computer time sync From: "tdick" dickthomas01@............. Date: Wed, 14 Apr 2004 20:52:28 -0500 I am using Dimension 4 to sync the time on the computer that runs only WinSDR. My time seems to vary. In an event yesterday, St. Louis network and my computer were 20 seconds off for the same event. Any suggestions? __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: computer time sync From: sismos@.............. Date: Thu, 15 Apr 2004 02:41:10 +0000 Hello, I also have notice over the last year that that it is harder to get good time from timeservers. Every little Dlink dsl router (and most other brands) have time clients and the timeservers in many cases can't respond in a timely way because of the huge number of request. I now have my main computer with a GPS and I send the time with Tardis to all the computers on my network who listen with K9 it is a bit better. I am slowly moving to GPS on all systems. Consider GPS or WWV You also might consider using Righttime software, I would hold your time much better than 20 seconds. I think all station should have good time. Angel Thursday, April 15, 2004, 1:52:28 AM, you wrote: t> I am using Dimension 4 to sync the time on the computer that runs only t> WinSDR. My time seems to vary. In an event yesterday, St. Louis network and t> my computer were 20 seconds off for the same event. Any suggestions? t> __________________________________________________________ t> Public Seismic Network Mailing List (PSN-L) t> To leave this list email PSN-L-REQUEST@.............. with t> the body of the message (first line only): unsubscribe t> See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: 1906 epicenter data From: "Kareem Lanier" kareem@............. Date: Wed, 14 Apr 2004 19:46:42 -0700 Does anyone know where I can get the latest information on the 1906 epicenter? Kareem ---------------------------------------------------------------------------- ------------------- Kareem's HeyJooJoo.Com - Discover, Explore, Learn & Play All of my outgoing and incoming emails are scanned for viruses and worms by my antivirus software.
Does anyone know where I can get the latest = information=20 on the 1906 epicenter?
 
 
Kareem
 
----------------------------------------------------------------= -------------------------------
Kareem's = HeyJooJoo.Com - Discover, Explore, = Learn &=20 Play
 
All of my = outgoing and=20 incoming emails are scanned for viruses and worms by my antivirus=20 software.
 
Subject: RE: 1906 epicenter data From: "Steve Hammond" shammon1@............. Date: Wed, 14 Apr 2004 21:15:33 -0700 Kereem, hereis a Berkeley Informational site with the info you requested. http://www.seismo.berkeley.edu/seismo/hayward/seismicity.hist_1906.html Regards, Steve Hammond PSN San Jose Aptos, CA -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Kareem Lanier Sent: Wednesday, April 14, 2004 7:47 PM To: PSN Subject: 1906 epicenter data Does anyone know where I can get the latest information on the 1906 epicenter? Kareem -------------------------------------------------------------------------- --------------------- Kareem's HeyJooJoo.Com - Discover, Explore, Learn & Play All of my outgoing and incoming emails are scanned for viruses and worms by my antivirus software.
Kereem, hereis a Berkeley Informational site with the info you = requested.=20
http://www.seismo.berkeley.edu/seismo/hayward/seismicity.hist_190= 6.html
 
Regards, Steve Hammond
PSN=20 San Jose  Aptos, CA
-----Original Message-----
From: = psn-l-request@................. [mailto:psn-l-request@...............On Behalf Of Kareem=20 Lanier
Sent: Wednesday, April 14, 2004 7:47 PM
To: = PSN
Subject: 1906 epicenter data

Does anyone know where I can get the latest = information on the 1906 epicenter?
 
 
Kareem
 
----------------------------------------------------------------= -------------------------------
Kareem's = HeyJooJoo.Com - Discover, Explore, = Learn &=20 Play
 
All of my = outgoing and=20 incoming emails are scanned for viruses and worms by my antivirus = software.
 
Subject: RE: 1906 epicenter data From: "Kareem Lanier" kareem@............. Date: Wed, 14 Apr 2004 21:21:45 -0700 Thanks Steve. Do you know if there's been any recent studies done on the precise epicenter of the 1906 event? Olema versus offshore of Daly City. Kareem _____ From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Steve Hammond Sent: Wednesday, April 14, 2004 9:16 PM To: psn-l@.............. Subject: RE: 1906 epicenter data Kereem, hereis a Berkeley Informational site with the info you requested. http://www.seismo.berkeley.edu/seismo/hayward/seismicity.hist_1906.html Regards, Steve Hammond PSN San Jose Aptos, CA -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Kareem Lanier Sent: Wednesday, April 14, 2004 7:47 PM To: PSN Subject: 1906 epicenter data Does anyone know where I can get the latest information on the 1906 epicenter? Kareem ---------------------------------------------------------------------------- ------------------- Kareem's HeyJooJoo.Com - Discover, Explore, Learn & Play All of my outgoing and incoming emails are scanned for viruses and worms by my antivirus software.
Thanks Steve. =
 
Do you know if = there's been any=20 recent studies done on the precise epicenter of the 1906 event?=20
Olema versus = offshore of Daly=20 City.
 
Kareem

From: psn-l-request@................. [mailto:psn-l-request@............... On Behalf Of Steve=20 Hammond
Sent: Wednesday, April 14, 2004 9:16 PM
To:=20 psn-l@..............
Subject: RE: 1906 epicenter=20 data

Kereem, hereis a Berkeley Informational site with the info you = requested.=20
http://www.seismo.berkeley.edu/seismo/hayward/seismicity.hist_190= 6.html
 
Regards, Steve Hammond
PSN=20 San Jose  Aptos, CA
-----Original Message-----
From: = psn-l-request@................. [mailto:psn-l-request@...............On Behalf Of Kareem=20 Lanier
Sent: Wednesday, April 14, 2004 7:47 PM
To: = PSN
Subject: 1906 epicenter data

Does anyone know where I can get the latest = information on the 1906 epicenter?
 
 
Kareem
 
----------------------------------------------------------------= -------------------------------
Kareem's = HeyJooJoo.Com - Discover, Explore, = Learn &=20 Play
 
All of my = outgoing and=20 incoming emails are scanned for viruses and worms by my antivirus = software.
 
Subject: RE: 1906 epicenter data From: "Steve Hammond" shammon1@............. Date: Wed, 14 Apr 2004 22:13:39 -0700 Hi Kareem. I'm not aware of any new studies. The USGS Professional Paper 1515, The San Andreas Fault System, Calif., provides the following: 1906/04/18 13:12 UTC 37*24' Lat N. 121*54' Long W. This location is right off the cost near UCSF. Olema is credited with having the peak displacement of 6m measured. Regards, Steve PSN San Jose Aptos, CA [Steve Hammond] Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Kareem Lanier Sent: Wednesday, April 14, 2004 9:22 PM To: psn-l@.............. Subject: RE: 1906 epicenter data Thanks Steve. Do you know if there's been any recent studies done on the precise epicenter of the 1906 event? Olema versus offshore of Daly City. Kareem ---------------------------------------------------------------------------- -- From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Steve Hammond Sent: Wednesday, April 14, 2004 9:16 PM To: psn-l@.............. Subject: RE: 1906 epicenter data Kereem, hereis a Berkeley Informational site with the info you requested. http://www.seismo.berkeley.edu/seismo/hayward/seismicity.hist_1906.html Regards, Steve Hammond PSN San Jose Aptos, CA -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Kareem Lanier Sent: Wednesday, April 14, 2004 7:47 PM To: PSN Subject: 1906 epicenter data Does anyone know where I can get the latest information on the 1906 epicenter? Kareem ------------------------------------------------------------------------ ----------------------- Kareem's HeyJooJoo.Com - Discover, Explore, Learn & Play All of my outgoing and incoming emails are scanned for viruses and worms by my antivirus software.
Hi=20 Kareem. I'm not aware of any new studies. The USGS Professional Paper = 1515, The=20 San Andreas Fault System, Calif., provides the = following:
1906/04/18 13:12 UTC  37*24' Lat N. 121*54' Long W.  = This=20 location is right off the cost near UCSF. Olema is credited with having = the peak=20 displacement of 6m measured.
Regards, Steve
PSN San = Jose Aptos,=20 CA
[Steve=20 Hammond] 
 Message-----
From:=20 psn-l-request@.............. [mailto:psn-l-request@...............On = Behalf=20 Of Kareem Lanier
Sent: Wednesday, April 14, 2004 9:22=20 PM
To: psn-l@..............
Subject: RE: 1906 = epicenter=20 data

Thanks Steve.=20
 
Do you know if = there's been any=20 recent studies done on the precise epicenter of the 1906 event?=20
Olema versus = offshore of Daly=20 City.
 
Kareem

From: psn-l-request@.............. = [mailto:psn-l-request@............... On Behalf Of Steve=20 Hammond
Sent: Wednesday, April 14, 2004 9:16 = PM
To:=20 psn-l@..............
Subject: RE: 1906 epicenter=20 data

Kereem, hereis a Berkeley Informational site with the info = you=20 requested.
http://www.seismo.berkeley.edu/seismo/hayward/seismicity.hist_190= 6.html
 
Regards, Steve Hammond
PSN=20 San Jose  Aptos, CA
-----Original Message-----
From:=20 psn-l-request@.............. = [mailto:psn-l-request@...............On=20 Behalf Of Kareem Lanier
Sent: Wednesday, April 14, = 2004 7:47=20 PM
To: PSN
Subject: 1906 epicenter=20 data

Does anyone know where I can get the = latest=20 information on the 1906 epicenter?
 
 
Kareem
 
----------------------------------------------------------------= -------------------------------
Kareem's = HeyJooJoo.Com - Discover, Explore, = Learn=20 & Play
 
All of = my outgoing and=20 incoming emails are scanned for viruses and worms by my = antivirus=20 software.
 
Subject: Re: computer time sync From: "Larry Cochrane" lcochrane@.............. Date: Thu, 15 Apr 2004 01:20:25 -0700 The time stamping of the data is preformed on the A/D board not on the computer running WinSDR. If you want very accurate timing, down to a few milliseconds, you will need to use GPS. The GPS receiver connects up to the A/D board so it can uses the highly accuracy 1 pulse per second signal generated by the GPS receiver to time stamp the data. See http://www.seismicnet.com/gps/index.html for a GPS timing system that will work with my A/D board. You can use the computer running WinSDR to supply timing information to the A/D board. In the WinSDR system settings dialog box select "Local" timing reference type. When this timing mode is selected the A/D board interrogates the computer for the current time of day. I found that the NT port of NTP works very well under Win2K. If you have a DSL line, and can find a good time server that is near by, you can achieve a timing accuracy of around 10 to 20 milliseconds. While searching around I found this Windows port of NTP: http://home.att.net/~Tom.Horsley/ntptime.html Larry Cochrane Redwood City, PSN ----- Original Message ----- From: "tdick" To: Cc: "Kevin Bach" Sent: Wednesday, April 14, 2004 6:52 PM Subject: computer time sync > I am using Dimension 4 to sync the time on the computer that runs only > WinSDR. My time seems to vary. In an event yesterday, St. Louis network and > my computer were 20 seconds off for the same event. Any suggestions? > > > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: computer time sync From: Ian Smith ian@........... Date: Thu, 15 Apr 2004 09:40:19 +0100 for the purposes of our psn uses (plotting quake location etc) what is the error budget for timing?  I've never seen this discussed. 

There must be a fundamental limit caused by the variation in travel times through the earth.  Ie, if the same quake happened twice some thousands of miles away, what would the typical variation in travel time through the earth be?

Another limit will be the algorthms used to calculate the distance from the S and P waves.  Also, the accuracy on our traces with which we place the S and P pointers.  I suspect that this is the largest source of error and may be the equivalent of many many seconds.

Ian Smith

Larry Cochrane wrote:
The time stamping of the data is preformed on the A/D board not on the
computer running WinSDR. If you want very accurate timing, down to a few
milliseconds, you will need to use GPS. The GPS receiver connects up to the
A/D board so it can uses the highly accuracy 1 pulse per second signal
generated by the GPS receiver to time stamp the data. See
http://www.seismicnet.com/gps/index.html for a GPS timing system that will
work with my A/D board.

You can use the computer running WinSDR to supply timing information to the
A/D board. In the WinSDR system settings dialog box select "Local" timing
reference type. When this timing mode is selected the A/D board interrogates
the computer for the current time of day.

I found that the NT port of NTP works very well under Win2K. If you have a
DSL line, and can find a good time server that is near by, you can achieve a
timing accuracy of around 10 to 20 milliseconds. While searching around I
found this Windows port of NTP:
http://home.att.net/~Tom.Horsley/ntptime.html

Larry Cochrane
Redwood City, PSN


----- Original Message ----- 
From: "tdick" <dickthomas01@.............>
To: <psn-l@..............>
Cc: "Kevin Bach" <bachcottage@...........>
Sent: Wednesday, April 14, 2004 6:52 PM
Subject: computer time sync


  
I am using Dimension 4 to sync the time on the computer that runs only
WinSDR. My time seems to vary. In an event yesterday, St. Louis network
    
and
  
my computer were 20 seconds off for the same event. Any suggestions?


__________________________________________________________

Public Seismic Network Mailing List (PSN-L)

To leave this list email PSN-L-REQUEST@.............. with
the body of the message (first line only): unsubscribe
See http://www.seismicnet.com/maillist.html for more information.

    

__________________________________________________________

Public Seismic Network Mailing List (PSN-L)

To leave this list email PSN-L-REQUEST@.............. with 
the body of the message (first line only): unsubscribe
See http://www.seismicnet.com/maillist.html for more information.
Subject: RE: 1906 epicenter data From: "Kareem Lanier" kareem@............. Date: Thu, 15 Apr 2004 06:14:36 -0700 gosh. I've searched the USGS website for that professional paper and cannot seem to find it. It's 1515, for sure? Kareem _____ From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Steve Hammond Sent: Wednesday, April 14, 2004 10:14 PM To: psn-l@.............. Subject: RE: 1906 epicenter data Hi Kareem. I'm not aware of any new studies. The USGS Professional Paper 1515, The San Andreas Fault System, Calif., provides the following: 1906/04/18 13:12 UTC 37*24' Lat N. 121*54' Long W. This location is right off the cost near UCSF. Olema is credited with having the peak displacement of 6m measured. Regards, Steve PSN San Jose Aptos, CA [Steve Hammond] Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Kareem Lanier Sent: Wednesday, April 14, 2004 9:22 PM To: psn-l@.............. Subject: RE: 1906 epicenter data Thanks Steve. Do you know if there's been any recent studies done on the precise epicenter of the 1906 event? Olema versus offshore of Daly City. Kareem _____ From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Steve Hammond Sent: Wednesday, April 14, 2004 9:16 PM To: psn-l@.............. Subject: RE: 1906 epicenter data Kereem, hereis a Berkeley Informational site with the info you requested. http://www.seismo.berkeley.edu/seismo/hayward/seismicity.hist_1906.html Regards, Steve Hammond PSN San Jose Aptos, CA -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Kareem Lanier Sent: Wednesday, April 14, 2004 7:47 PM To: PSN Subject: 1906 epicenter data Does anyone know where I can get the latest information on the 1906 epicenter? Kareem ---------------------------------------------------------------------------- ------------------- Kareem's HeyJooJoo.Com - Discover, Explore, Learn & Play All of my outgoing and incoming emails are scanned for viruses and worms by my antivirus software.
gosh. I've searched = the USGS=20 website for that professional paper and cannot seem to find it. It's = 1515, for=20 sure?
 
Kareem

From: psn-l-request@................. [mailto:psn-l-request@............... On Behalf Of Steve=20 Hammond
Sent: Wednesday, April 14, 2004 10:14 PM
To: = psn-l@..............
Subject: RE: 1906 epicenter=20 data

Hi=20 Kareem. I'm not aware of any new studies. The USGS Professional Paper = 1515, The=20 San Andreas Fault System, Calif., provides the = following:
1906/04/18 13:12 UTC  37*24' Lat N. 121*54' Long W.  = This=20 location is right off the cost near UCSF. Olema is credited with having = the peak=20 displacement of 6m measured.
Regards, Steve
PSN San = Jose Aptos,=20 CA
[Steve=20 Hammond] 
 Message-----
From:=20 psn-l-request@.............. [mailto:psn-l-request@...............On = Behalf=20 Of Kareem Lanier
Sent: Wednesday, April 14, 2004 9:22=20 PM
To: psn-l@..............
Subject: RE: 1906 = epicenter=20 data

Thanks Steve.=20
 
Do you know if = there's been any=20 recent studies done on the precise epicenter of the 1906 event?=20
Olema versus = offshore of Daly=20 City.
 
Kareem

From: psn-l-request@.............. = [mailto:psn-l-request@............... On Behalf Of Steve=20 Hammond
Sent: Wednesday, April 14, 2004 9:16 = PM
To:=20 psn-l@..............
Subject: RE: 1906 epicenter=20 data

Kereem, hereis a Berkeley Informational site with the info = you=20 requested.
http://www.seismo.berkeley.edu/seismo/hayward/seismicity.hist_190= 6.html
 
Regards, Steve Hammond
PSN=20 San Jose  Aptos, CA
-----Original Message-----
From:=20 psn-l-request@.............. = [mailto:psn-l-request@...............On=20 Behalf Of Kareem Lanier
Sent: Wednesday, April 14, = 2004 7:47=20 PM
To: PSN
Subject: 1906 epicenter=20 data

Does anyone know where I can get the = latest=20 information on the 1906 epicenter?
 
 
Kareem
 
----------------------------------------------------------------= -------------------------------
Kareem's = HeyJooJoo.Com - Discover, Explore, = Learn=20 & Play
 
All of = my outgoing and=20 incoming emails are scanned for viruses and worms by my = antivirus=20 software.
 
Subject: Re: computer time sync From: "tdick" dickthomas01@............. Date: Thu, 15 Apr 2004 08:22:43 -0500 Ian.. I sensed a frustration when trying to talk to Dr. Hermann at the St. = Louis U. network about the location of regional mine blasts. On longer = distant earthquakes -- and most are a long way from the Midwest --like = last night's Jan Mayen Island earthquake --- the arrival of P according = to the tables what happen was off by about 10 seconds--- the computer is = running at 200 Hz -- it may be loading down.
Ian..
I sensed a frustration when trying to = talk to Dr.=20 Hermann at the St. Louis U. network about the location of regional = mine=20 blasts. On longer distant earthquakes -- and most are a long way from = the=20 Midwest --like last night's Jan Mayen Island earthquake --- the arrival of P according to the = tables what=20 happen was off by about 10 seconds--- the computer is = running at=20 200 Hz -- it may be loading down.
Subject: Re: computer time sync From: "Larry Cochrane" lcochrane@.............. Date: Thu, 15 Apr 2004 21:02:22 -0700 Good question. I would say it depends on the type of earthquakes you will be recording. If you only record teleseismic events, then anything under 1/4 of a second is probably overkill. If you record local events, then the timing should be more accurate. The travel-time tables that WinQuake uses can be very accurate. If an agency accurately reports the location and time of a teleseismic event, WinQuake can place the P and S markers to within a few seconds of the actual arrival time of the wave. Now picking the location of the P and especially the S is another story.... Larry Cochrane Redwood City, PSN ----- Original Message ----- From: "Ian Smith" To: Sent: Thursday, April 15, 2004 1:40 AM Subject: Re: computer time sync > for the purposes of our psn uses (plotting quake location etc) what is the error budget for timing? I've never seen this discussed. > > There must be a fundamental limit caused by the variation in travel times through the earth. Ie, if the same quake happened twice some thousands of miles away, what would the typical variation in travel time through the earth be? > > Another limit will be the algorthms used to calculate the distance from the S and P waves. Also, the accuracy on our traces with which we place the S and P pointers. I suspect that this is the largest source of error and may be the equivalent of many many seconds. > > Ian Smith __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: 1906 epicenter data From: "Connie and Jim Lehman" lehmancj@........... Date: Fri, 16 Apr 2004 07:56:44 -0400 Quake enthusiasts-- The interest in 1906 event never goes away, especially with the = centennial approaching. Olema is mentioned. This is a "must see" site = for anyone --expecially us easterners--seeking the effects of faulting = at the surface. The National Park Service visitor center is just off = Rt. 1 about 20 miles north of Golden Gate Bridge. The excursion getting = there is a scenic adventure in itself.... Jim Lehman
Quake = enthusiasts--
  The interest in 1906 event never = goes away,=20 especially with the centennial  approaching.  Olema is=20 mentioned.  This is a "must see" site for anyone --expecially us=20 easterners--seeking the effects of faulting at the surface.  The = National=20 Park Service visitor center is just off Rt. 1 about 20 miles north of = Golden=20 Gate Bridge.  The excursion getting there is a scenic = adventure in=20 itself....
          =             &= nbsp;           &n= bsp;           =20 Jim Lehman
 
Subject: RE: 1906 epicenter data From: "Kareem Lanier" kareem@............. Date: Fri, 16 Apr 2004 06:14:36 -0700 Yeah, I agree. I've visited the park in the Point Reyes area where you can take the "Earthquake Trail". There, you'll see the offset fence posts and a tree which was split by the strike-slip rupturing. I believe they still hold the concept that the epicenter is around Olema. It seems that the USGS mostly agrees with this but UC Berkeley tends to push for a 1906 epicenter just offshore of Daly City. I cant seem to find any documentation that discusses this to any detail. Kareem _____ From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Connie and Jim Lehman Sent: Friday, April 16, 2004 4:57 AM To: psn-l@.............. Subject: Re: 1906 epicenter data Quake enthusiasts-- The interest in 1906 event never goes away, especially with the centennial approaching. Olema is mentioned. This is a "must see" site for anyone --expecially us easterners--seeking the effects of faulting at the surface. The National Park Service visitor center is just off Rt. 1 about 20 miles north of Golden Gate Bridge. The excursion getting there is a scenic adventure in itself.... Jim Lehman
Yeah, I agree. I've = visited the=20 park in the Point Reyes area where you can take the "Earthquake Trail". = There,=20 you'll see the offset fence posts and a tree which was split by the = strike-slip=20 rupturing. I believe they still hold the concept that the epicenter is = around=20 Olema. It seems that the USGS mostly agrees with this but UC Berkeley = tends to=20 push for a 1906 epicenter just offshore of Daly City. I cant seem to = find any=20 documentation that discusses this to any detail.
 
Kareem

From: psn-l-request@................. [mailto:psn-l-request@............... On Behalf Of Connie and Jim = Lehman
Sent: Friday, April 16, 2004 4:57 AM
To:=20 psn-l@..............
Subject: Re: 1906 epicenter=20 data

Quake = enthusiasts--
  The interest in 1906 event never = goes away,=20 especially with the centennial  approaching.  Olema is=20 mentioned.  This is a "must see" site for anyone --expecially us=20 easterners--seeking the effects of faulting at the surface.  The = National=20 Park Service visitor center is just off Rt. 1 about 20 miles north of = Golden=20 Gate Bridge.  The excursion getting there is a scenic = adventure in=20 itself....
          =             &= nbsp;           &n= bsp;           =20 Jim Lehman
 
Subject: RE: 1906 epicenter data From: "Steve Hammond" shammon1@............. Date: Fri, 16 Apr 2004 10:44:00 -0700 Hi Jim- Hi Kareem, I agree Jim-- The Olema area is worth going to visit. Just don't try to do it on a summer day when the rest of San Francisco is trying to go to the beach like I did. Kereem, you asked about US Geological Survey Professional Paper 1515, The San Andreas Fault System, California (1990) Library of Congress QE606.5.U6S26. This text is actually a 283 page book I purchased from the USGS bookstore in 1991. It details all the fault system and each of the principal earthquakes. Below, please find the text on the 1906 event (page 159-161). There is a discussion in the second part about the work completed to determine the magnitude. There is also a discussion before that on the epicenter location. You will see the USGS references two citations, Bolt, 1968 and Boore, 1977. Keep in mind, Bolt was a Professor at UC Berkeley where he did the research on the location of the 1906 event. I would expect Berkeley to back Bolt's findings. I found it odd that Bolt never publishes his findings in his own books. For example, in Earthquake, Bolt 1978 and in Earthquakes and Geological Discovery (1993) he simply states, "April 18, 1906, early morning in California.... At 5:12 A.M., a few kilometers from the Golden Gate..." Another interesting point, Charles Richter in Elementary Seismology (1958) lists the epicenter location to be 38N 123W 8.3 13:12.0 UTC which is the location of Point Reyes west of the fault system. Regards, Steve Hammond PSN San Jose Aptos, CA APRIL 18, 1906 (M=8V4) The California earthquake of April 18, 1906, ranks as one of the most significant earthquakes of all time. Today, its importance comes more from the wealth of scientific knowledge derived from it than from its sheer size. Rupturing the northernmost 430 km of the San Andreas fault from northwest of San Juan Bautista to the triple junction at Cape Mendocino (fig. 6.6), the earth-quake confounded contemporary geologists with its large, horizontal displacements and great rupture length. Indeed, the significance of the fault and recognition of its large cumulative offset would not be fully appreciated until the advent of plate tectonics more than half a century later. Analysis of the 1906 displacements and strain in the surrounding crust led Reid (1910) to formulate his elastic-rebound theory of the earthquake source, which remains today the principal model of the earthquake cycle. As a basic reference about the earthquake and the damage it caused, geologic observations of the fault rupture and shaking effects, and other consequences of the earthquake, Lawson's (1908) report remains the authoritative work, as well as arguably the most impor-tant study of a single earthquake. In the public's mind, this earthquake is perhaps remembered most for the fire it spawned in San Francisco, giving it the somewhat misleading appellation of the "San Francisco earthquake" (fig. 6.7). Shaking damage, however, was equally severe in many other places along the fault rupture. The frequently quoted value of 700 deaths caused by the earthquake and fire is now believed to underestimate the total loss of life by a factor of 3 or 4. Most of the fatalities occurred in San Francisco, and 189 were reported else-where. At almost precisely 5:12 a.m. local time, a foreshock occurred with sufficient force to be felt widely through-out the San Francisco Bay area. The great earthquake broke loose some 20 to 25 s later, with an epicenter near San Francisco (Bolt, 1968; Boore, 1977). Violent shocks punctuated the strong shaking, which lasted some 45 to 60 s. The earthquake was felt from southern Oregon to south of Los Angeles and inland as far as central Nevada (fig. 6.6). The highest MMI's of VII to IX paralleled the length of the rupture, extending as far as 80 km inland from the fault trace. One important characteristic of the shaking intensity noted in Lawson's (1908) report was the clear correlation of intensity with underlying geologic conditions. Areas situated in sediment-filled valleys sus-tained stronger shaking than nearby bedrock sites, and the strongest shaking occurred in areas where groundreclaimed from San Francisco Bay failed in the earth-quake. Modern seismic-zonation practice accounts for the differences in seismic hazard posed by varying geologic conditions (see Borcherdt, 1975, and Ziony, 1985, for analyses of the San Francisco Bay and Los Angeles regions, respectively). The characteristics and amount of surface fault slip in this earthquake varied to a remarkable degree along the length of the rupture. Peak displacements of 6 m were measured near Olema on the Point Reyes peninsula, where the surface trace of the rupture formed a sharp, well-defined break (fig. 6.8). In contrast, the fault break was extremely difficult to recognize along its southern-most 90 km, where the surface offset averaged only about P/2 m or less (see chap. 7). The magnitude of 8.3 commonly quoted for the 1906 earthquake comes from Richter (1958) and, within the precision of reporting, is identical to the 8V4 listed by Gutenberg and Richter (1954). Table 6.1 also lists other magnitudes for this earthquake, derived from recent analyses of both the same data used by Gutenberg and Richter and new data. Strictly speaking, a "Richter magnitude" (ML) for the earthquake cannot be deter-mined because no appropriate seismographs were in operation at the time. Jennings and Kanamori (1979) used related measurements extracted from simple pendulums at Yountville, Calif., and Carson City, Nev., to derive ML=6.9, substantially smaller than the traditionally quoted value. ML, which is based on the single largest peak on a seismogram at approximately 1-s period and takes into account neither the duration of the event nor longer period motions, is saturated for this event. Geller and Kanamori (1977) used the unpublished worksheets of Gutenberg and Richter to compute a body-wave magnitude of mb=7A, using the procedure of Gutenberg and Richter (1956). Because long-period (14 s) P-waves were used in this calculation, it cannot be directly compared to the short-period mb values routinely reported today. Other workers since Gutenberg and Richter have studied the long-period surface waves of the 1906 earth-quake and computed Ms values. Bolt (1968) confirmed an Ms of about 8V4, whereas Lienkaemper (1984) found Ms= 8.3 from an analysis of all the records collected by Reid (1910). Lienkaemper's magnitude combined data from both damped and undamped instruments, correcting each for magnification at the appropriate period of motion. Abe (1988), who analyzed only the undamped Milne seismograms, obtained Ms= 7.8, using slightly different procedures and a systematic set of station-magnitude corrections. Also, the four damped seismometers (all in Europe) give Ms=8.1. Longer period (50-100 s) surface waves analyzed by Thatcher (1975) indicate a seismic moment of 4xl027 dyne-cm, equivalent to M=7.7, in agreement with the seismic moment of 5xl027 dyne-cm obtained from geodetic data, thus giving M=7.8 (Thatch-er and Lisowski, 1987). Finally, Toppozada and Parke (1982) assigned an intensity magnitude (M/) of 7.8 on the basis of the total area (48,000 km2) undergoing shaking of MMI VII or higher. The "traditional" magnitude of 8V4 is retained here, except where seismic moment is used for quantitative purposes. -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Kareem Lanier Sent: Friday, April 16, 2004 6:15 AM To: psn-l@.............. Subject: RE: 1906 epicenter data Yeah, I agree. I've visited the park in the Point Reyes area where you can take the "Earthquake Trail". There, you'll see the offset fence posts and a tree which was split by the strike-slip rupturing. I believe they still hold the concept that the epicenter is around Olema. It seems that the USGS mostly agrees with this but UC Berkeley tends to push for a 1906 epicenter just offshore of Daly City. I cant seem to find any documentation that discusses this to any detail. Kareem ---------------------------------------------------------------------------- -- From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Connie and Jim Lehman Sent: Friday, April 16, 2004 4:57 AM To: psn-l@.............. Subject: Re: 1906 epicenter data Quake enthusiasts-- The interest in 1906 event never goes away, especially with the centennial approaching. Olema is mentioned. This is a "must see" site for anyone --expecially us easterners--seeking the effects of faulting at the surface. The National Park Service visitor center is just off Rt. 1 about 20 miles north of Golden Gate Bridge. The excursion getting there is a scenic adventure in itself.... Jim Lehman
Hi=20 Jim- Hi Kareem,
 I agree Jim-- The Olema area is worth going to = visit. =20 Just don't try to do it on a summer day when the rest of San Francisco = is trying=20 to go to the beach like I did. Kereem, you asked about US Geological = Survey=20 Professional Paper 1515, The San Andreas Fault System, California (1990) = Library=20 of Congress QE606.5.U6S26. This text is actually a 283 page book I = purchased=20 from the USGS bookstore in 1991. It details all the fault = system=20 and each of the principal earthquakes. Below, please find=20 the text on the 1906 event (page 159-161). There is a=20 discussion in the second part about the work completed to = determine the magnitude. There is also a discussion before that on the = epicenter=20 location. You will see the USGS references two citations, Bolt, = 1968 and=20 Boore, 1977.  Keep in mind, Bolt was a Professor at UC Berkeley = where he=20 did the research on the location of the 1906 event. I would = expect=20 Berkeley to back Bolt's findings. I found it odd that Bolt never = publishes=20 his findings in his own books. For example, in Earthquake, Bolt = 1978 and in=20 Earthquakes and Geological Discovery (1993) he simply states, = "April=20 18, 1906, early morning in California.... At 5:12 A.M., a few kilometers = from=20 the Golden Gate..." Another interesting point, Charles Richter in=20 Elementary Seismology (1958) lists the epicenter location to=20 be 38N 123W 8.3 13:12.0 UTC which is the location of Point = Reyes west=20 of the fault system.
Regards, Steve Hammond
PSN=20 San Jose  Aptos, CA    
 

APRIL=20 18, 1906=20 (M=3D8V4)

The California earthquake of = April 18,=20 1906, ranks as one of the most = significant=20 earthquakes of all time. Today, its=20 importance comes more from the wealth of scientific knowledge = derived=20 from it than from its sheer size. = Rupturing=20 the northernmost 430 km of the San Andreas fault from northwest of San = Juan=20 Bautista to the triple junction at Cape Mendocino (fig. 6.6), the = earth­quake confounded = contemporary=20 geologists with its large,=20 horizontal displacements and great rupture length. Indeed, the significance of the fault = and=20 recognition of its large cumulative offset would not be fully = appreciated=20 until the advent of plate = tectonics more=20 than half a century later. Analysis of the 1906 displacements and = strain in the surrounding crust led = Reid (1910)=20 to formulate his = elastic-rebound=20 theory of the earthquake source,=20 which remains today the principal model of the earthquake cycle.

As a = basic=20 reference about the earthquake and the damage it caused, geologic = observations=20 of the fault rupture = and=20 shaking effects, and other consequences of the earthquake, Lawson's = (1908)=20 report remains the authoritative work, as well as = arguably=20 the most impor­tant study of = a single=20 earthquake. In the public's mind, this earthquake is perhaps remembered = most for=20 the fire it spawned in San Francisco, giving it the somewhat = misleading appellation of the "San = Francisco=20 earthquake" (fig. 6.7). = Shaking=20 damage, however, was equally severe in many other places along the fault = rupture. The=20 frequently quoted value of 700 deaths caused by the earthquake and fire is now believed to = underestimate the total = loss of=20 life by a factor of 3 or 4. Most of the fatalities occurred in San Francisco, and 189 were = reported=20 else­where.

At = almost=20 precisely 5:12 a.m. local time, a foreshock occurred with=20 sufficient force to be felt widely through­out the = San=20 Francisco Bay area. The great earthquake broke loose some 20 to 25 s = later, with an=20 epicenter near San Francisco = (Bolt, 1968;=20 Boore, 1977). Violent shocks punctuated the strong shaking, which = lasted some=20 45 to 60 s. The earthquake was felt from southern Oregon to south of Los Angeles and inland as far = as=20 central Nevada (fig. 6.6). The highest MMI's of VII to IX paralleled the = length of the rupture, = extending as=20 far as 80 km inland from the fault trace. One important = characteristic of=20 the shaking intensity noted in = Lawson's=20 (1908) report was the clear correlation of intensity with = underlying=20 geologic conditions. Areas = situated in=20 sediment-filled valleys sus­tained stronger shaking than nearby = bedrock sites,=20 and the strongest shaking = occurred=20 in areas where groundreclaimed from=20 San Francisco Bay failed in the earth­quake. Modern seismic-zonation = practice accounts=20 for the differences in = seismic=20 hazard posed by varying geologic conditions (see Borcherdt, 1975, and = Ziony,=20 1985, for analyses of the = San=20 Francisco Bay and Los Angeles regions, respectively).

The=20 characteristics and amount of surface fault slip in this = earthquake=20 varied to a remarkable degree along the length of the rupture. Peak = displacements=20 of 6 m were measured near Olema on = the Point=20 Reyes peninsula, where the surface trace of the rupture formed a sharp,=20 well-defined break (fig. = 6.8). In=20 contrast, the fault break was extremely difficult to recognize = along its=20 southern­most 90 km, where = the surface=20 offset averaged only about P/2 m or=20 less (see chap. 7).

The = magnitude of=20 8.3 commonly quoted for the 1906 earthquake comes=20 from Richter (1958) and, within the precision of=20 reporting, is identical to the 8V4 listed by Gutenberg and=20 Richter (1954). Table 6.1 also lists other magnitudes for=20 this earthquake, derived from recent analyses of both the same data = used by=20 Gutenberg and Richter and new = data. Strictly=20 speaking, a "Richter magnitude"=20 (ML) for the earthquake cannot be = deter­mined because no appropriate = seismographs were=20 in

operation at the=20 time. Jennings and Kanamori (1979) used related measurements extracted = from simple=20 pendulums at Yountville, Calif., and Carson City, Nev., to derive ML=3D6.9, substantially = smaller than the=20 traditionally quoted value. ML, which is based = on the=20 single largest peak on a seismogram at approximately 1-s period and = takes into account neither the duration = of the=20 event nor longer period = motions, is=20 saturated for this event.

Geller = and=20 Kanamori (1977) used the unpublished worksheets of=20 Gutenberg and Richter to compute a body-wave=20 magnitude of mb=3D7A, using the procedure of = Gutenberg and=20 Richter (1956). Because long-period (14 s) P-waves = were used=20 in this calculation, it cannot be directly = compared=20 to the short-period mb values routinely reported = today.

Other = workers since=20 Gutenberg and Richter have studied = the=20 long-period surface waves of the 1906 earth­quake = and=20 computed Ms values. Bolt (1968) confirmed an = Ms=20 of = about 8V4,=20 whereas Lienkaemper (1984) found Ms=3D 8.3 = from an=20 analysis of all the records collected by Reid (1910). Lienkaemper's magnitude = combined=20 data from both damped and = undamped=20 instruments, correcting each for=20 magnification at the appropriate period of motion. Abe (1988), who analyzed only the = undamped Milne=20 seismograms, obtained Ms=3D 7.8, using slightly = different=20 procedures and a systematic set = of=20 station-magnitude corrections. Also, the four damped seismometers = (all in=20 Europe) give Ms=3D8.1. Longer period (50-100 s) surface waves analyzed by Thatcher (1975) = indicate a=20 seismic moment of 4xl027 dyne-cm, equivalent to = M=3D7.7, in=20 agreement with the seismic = moment of=20 5xl027 dyne-cm obtained from geodetic data, thus giving = M=3D7.8=20 (Thatch­er and Lisowski, 1987). Finally, Toppozada and Parke = (1982) assigned an intensity magnitude = (M/) of=20 7.8 on the basis of the total area (48,000 km2) undergoing = shaking of=20 MMI VII or = higher.

The = "traditional"=20 magnitude of 8V4 is retained here, except where seismic moment is = used for=20 quantitative purposes.

-----Original Message-----
From: = psn-l-request@................. [mailto:psn-l-request@...............On Behalf Of Kareem=20 Lanier
Sent: Friday, April 16, 2004 6:15 AM
To:=20 psn-l@..............
Subject: RE: 1906 epicenter=20 data

Yeah, I agree. = I've visited the=20 park in the Point Reyes area where you can take the "Earthquake = Trail". There,=20 you'll see the offset fence posts and a tree which was split by the=20 strike-slip rupturing. I believe they still hold the concept that the=20 epicenter is around Olema. It seems that the USGS mostly agrees with = this but=20 UC Berkeley tends to push for a 1906 epicenter just offshore of Daly = City. I=20 cant seem to find any documentation that discusses this to any=20 detail.
 
Kareem

From: psn-l-request@.............. = [mailto:psn-l-request@............... On Behalf Of Connie and = Jim=20 Lehman
Sent: Friday, April 16, 2004 4:57 AM
To:=20 psn-l@..............
Subject: Re: 1906 epicenter=20 data

Quake = enthusiasts--
  The interest in 1906 event = never goes=20 away, especially with the centennial  approaching.  Olema is = mentioned.  This is a "must see" site for anyone --expecially us=20 easterners--seeking the effects of faulting at the surface.  The = National=20 Park Service visitor center is just off Rt. 1 about 20 miles north of = Golden=20 Gate Bridge.  The excursion getting there is a scenic = adventure in=20 itself....
          =             &= nbsp;           &n= bsp;           =20 Jim Lehman
 
Subject: RE: 1906 epicenter data From: "Kareem Lanier" kareem@............. Date: Fri, 16 Apr 2004 18:59:36 -0700 Wow, you raised many interesting and intriguing points Steve. Thank you and everyone else very much. I'll see if I can obtain that book from the USGS bookstore. Kind of ominous to think that the epicenter was just southeast of the San Francisco State University. I imagine that things might have been worse if it had been located even further south. Kareem _____ From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Steve Hammond Sent: Friday, April 16, 2004 10:44 AM To: psn-l@.............. Subject: RE: 1906 epicenter data Hi Jim- Hi Kareem, I agree Jim-- The Olema area is worth going to visit. Just don't try to do it on a summer day when the rest of San Francisco is trying to go to the beach like I did. Kereem, you asked about US Geological Survey Professional Paper 1515, The San Andreas Fault System, California (1990) Library of Congress QE606.5.U6S26. This text is actually a 283 page book I purchased from the USGS bookstore in 1991. It details all the fault system and each of the principal earthquakes. Below, please find the text on the 1906 event (page 159-161). There is a discussion in the second part about the work completed to determine the magnitude. There is also a discussion before that on the epicenter location. You will see the USGS references two citations, Bolt, 1968 and Boore, 1977. Keep in mind, Bolt was a Professor at UC Berkeley where he did the research on the location of the 1906 event. I would expect Berkeley to back Bolt's findings. I found it odd that Bolt never publishes his findings in his own books. For example, in Earthquake, Bolt 1978 and in Earthquakes and Geological Discovery (1993) he simply states, "April 18, 1906, early morning in California.... At 5:12 A.M., a few kilometers from the Golden Gate..." Another interesting point, Charles Richter in Elementary Seismology (1958) lists the epicenter location to be 38N 123W 8.3 13:12.0 UTC which is the location of Point Reyes west of the fault system. Regards, Steve Hammond PSN San Jose Aptos, CA APRIL 18, 1906 (M=8V4) The California earthquake of April 18, 1906, ranks as one of the most significant earthquakes of all time. Today, its importance comes more from the wealth of scientific knowledge derived from it than from its sheer size. Rupturing the northernmost 430 km of the San Andreas fault from northwest of San Juan Bautista to the triple junction at Cape Mendocino (fig. 6.6), the earth-quake confounded contemporary geologists with its large, horizontal displacements and great rupture length. Indeed, the significance of the fault and recognition of its large cumulative offset would not be fully appreciated until the advent of plate tectonics more than half a century later. Analysis of the 1906 displacements and strain in the surrounding crust led Reid (1910) to formulate his elastic-rebound theory of the earthquake source, which remains today the principal model of the earthquake cycle. As a basic reference about the earthquake and the damage it caused, geologic observations of the fault rupture and shaking effects, and other consequences of the earthquake, Lawson's (1908) report remains the authoritative work, as well as arguably the most impor-tant study of a single earthquake. In the public's mind, this earthquake is perhaps remembered most for the fire it spawned in San Francisco, giving it the somewhat misleading appellation of the "San Francisco earthquake" (fig. 6.7). Shaking damage, however, was equally severe in many other places along the fault rupture. The frequently quoted value of 700 deaths caused by the earthquake and fire is now believed to underestimate the total loss of life by a factor of 3 or 4. Most of the fatalities occurred in San Francisco, and 189 were reported else-where. At almost precisely 5:12 a.m. local time, a foreshock occurred with sufficient force to be felt widely through-out the San Francisco Bay area. The great earthquake broke loose some 20 to 25 s later, with an epicenter near San Francisco (Bolt, 1968; Boore, 1977). Violent shocks punctuated the strong shaking, which lasted some 45 to 60 s. The earthquake was felt from southern Oregon to south of Los Angeles and inland as far as central Nevada (fig. 6.6). The highest MMI's of VII to IX paralleled the length of the rupture, extending as far as 80 km inland from the fault trace. One important characteristic of the shaking intensity noted in Lawson's (1908) report was the clear correlation of intensity with underlying geologic conditions. Areas situated in sediment-filled valleys sus-tained stronger shaking than nearby bedrock sites, and the strongest shaking occurred in areas where groundreclaimed from San Francisco Bay failed in the earth-quake. Modern seismic-zonation practice accounts for the differences in seismic hazard posed by varying geologic conditions (see Borcherdt, 1975, and Ziony, 1985, for analyses of the San Francisco Bay and Los Angeles regions, respectively). The characteristics and amount of surface fault slip in this earthquake varied to a remarkable degree along the length of the rupture. Peak displacements of 6 m were measured near Olema on the Point Reyes peninsula, where the surface trace of the rupture formed a sharp, well-defined break (fig. 6.8). In contrast, the fault break was extremely difficult to recognize along its southern-most 90 km, where the surface offset averaged only about P/2 m or less (see chap. 7). The magnitude of 8.3 commonly quoted for the 1906 earthquake comes from Richter (1958) and, within the precision of reporting, is identical to the 8V4 listed by Gutenberg and Richter (1954). Table 6.1 also lists other magnitudes for this earthquake, derived from recent analyses of both the same data used by Gutenberg and Richter and new data. Strictly speaking, a "Richter magnitude" (ML) for the earthquake cannot be deter-mined because no appropriate seismographs were in operation at the time. Jennings and Kanamori (1979) used related measurements extracted from simple pendulums at Yountville, Calif., and Carson City, Nev., to derive ML=6.9, substantially smaller than the traditionally quoted value. ML, which is based on the single largest peak on a seismogram at approximately 1-s period and takes into account neither the duration of the event nor longer period motions, is saturated for this event. Geller and Kanamori (1977) used the unpublished worksheets of Gutenberg and Richter to compute a body-wave magnitude of mb=7A, using the procedure of Gutenberg and Richter (1956). Because long-period (14 s) P-waves were used in this calculation, it cannot be directly compared to the short-period mb values routinely reported today. Other workers since Gutenberg and Richter have studied the long-period surface waves of the 1906 earth-quake and computed Ms values. Bolt (1968) confirmed an Ms of about 8V4, whereas Lienkaemper (1984) found Ms= 8.3 from an analysis of all the records collected by Reid (1910). Lienkaemper's magnitude combined data from both damped and undamped instruments, correcting each for magnification at the appropriate period of motion. Abe (1988), who analyzed only the undamped Milne seismograms, obtained Ms= 7.8, using slightly different procedures and a systematic set of station-magnitude corrections. Also, the four damped seismometers (all in Europe) give Ms=8.1. Longer period (50-100 s) surface waves analyzed by Thatcher (1975) indicate a seismic moment of 4xl027 dyne-cm, equivalent to M=7.7, in agreement with the seismic moment of 5xl027 dyne-cm obtained from geodetic data, thus giving M=7.8 (Thatch-er and Lisowski, 1987). Finally, Toppozada and Parke (1982) assigned an intensity magnitude (M/) of 7.8 on the basis of the total area (48,000 km2) undergoing shaking of MMI VII or higher. The "traditional" magnitude of 8V4 is retained here, except where seismic moment is used for quantitative purposes. -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@................. Behalf Of Kareem Lanier Sent: Friday, April 16, 2004 6:15 AM To: psn-l@.............. Subject: RE: 1906 epicenter data Yeah, I agree. I've visited the park in the Point Reyes area where you can take the "Earthquake Trail". There, you'll see the offset fence posts and a tree which was split by the strike-slip rupturing. I believe they still hold the concept that the epicenter is around Olema. It seems that the USGS mostly agrees with this but UC Berkeley tends to push for a 1906 epicenter just offshore of Daly City. I cant seem to find any documentation that discusses this to any detail. Kareem _____ From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Connie and Jim Lehman Sent: Friday, April 16, 2004 4:57 AM To: psn-l@.............. Subject: Re: 1906 epicenter data Quake enthusiasts-- The interest in 1906 event never goes away, especially with the centennial approaching. Olema is mentioned. This is a "must see" site for anyone --expecially us easterners--seeking the effects of faulting at the surface. The National Park Service visitor center is just off Rt. 1 about 20 miles north of Golden Gate Bridge. The excursion getting there is a scenic adventure in itself.... Jim Lehman
Wow, you raised many = interesting=20 and intriguing points Steve. Thank you and everyone else very much. = I'll=20 see if I can obtain that book from the USGS bookstore. =
Kind of ominous to = think that the=20 epicenter was just southeast of the San Francisco State University. I = imagine=20 that things might have been worse if it had been located even further=20 south.
 
Kareem
 

From: psn-l-request@................. [mailto:psn-l-request@............... On Behalf Of Steve=20 Hammond
Sent: Friday, April 16, 2004 10:44 AM
To:=20 psn-l@..............
Subject: RE: 1906 epicenter=20 data

Hi=20 Jim- Hi Kareem,
 I agree Jim-- The Olema area is worth going to = visit. =20 Just don't try to do it on a summer day when the rest of San Francisco = is trying=20 to go to the beach like I did. Kereem, you asked about US Geological = Survey=20 Professional Paper 1515, The San Andreas Fault System, California (1990) = Library=20 of Congress QE606.5.U6S26. This text is actually a 283 page book I = purchased=20 from the USGS bookstore in 1991. It details all the fault = system=20 and each of the principal earthquakes. Below, please find=20 the text on the 1906 event (page 159-161). There is a=20 discussion in the second part about the work completed to = determine the magnitude. There is also a discussion before that on the = epicenter=20 location. You will see the USGS references two citations, Bolt, = 1968 and=20 Boore, 1977.  Keep in mind, Bolt was a Professor at UC Berkeley = where he=20 did the research on the location of the 1906 event. I would = expect=20 Berkeley to back Bolt's findings. I found it odd that Bolt never = publishes=20 his findings in his own books. For example, in Earthquake, Bolt = 1978 and in=20 Earthquakes and Geological Discovery (1993) he simply states, = "April=20 18, 1906, early morning in California.... At 5:12 A.M., a few kilometers = from=20 the Golden Gate..." Another interesting point, Charles Richter in=20 Elementary Seismology (1958) lists the epicenter location to=20 be 38N 123W 8.3 13:12.0 UTC which is the location of Point = Reyes west=20 of the fault system.
Regards, Steve Hammond
PSN=20 San Jose  Aptos, CA    
 

APRIL=20 18, 1906=20 (M=3D8V4)

The California earthquake of = April 18,=20 1906, ranks as one of the most = significant=20 earthquakes of all time. Today, its=20 importance comes more from the wealth of scientific knowledge = derived=20 from it than from its sheer size. = Rupturing=20 the northernmost 430 km of the San Andreas fault from northwest of San = Juan=20 Bautista to the triple junction at Cape Mendocino (fig. 6.6), the = earth­quake confounded = contemporary=20 geologists with its large,=20 horizontal displacements and great rupture length. Indeed, the significance of the fault = and=20 recognition of its large cumulative offset would not be fully = appreciated=20 until the advent of plate = tectonics more=20 than half a century later. Analysis of the 1906 displacements and = strain in the surrounding crust led = Reid (1910)=20 to formulate his = elastic-rebound=20 theory of the earthquake source,=20 which remains today the principal model of the earthquake cycle.

As a = basic=20 reference about the earthquake and the damage it caused, geologic = observations=20 of the fault rupture = and=20 shaking effects, and other consequences of the earthquake, Lawson's = (1908)=20 report remains the authoritative work, as well as = arguably=20 the most impor­tant study of = a single=20 earthquake. In the public's mind, this earthquake is perhaps remembered = most for=20 the fire it spawned in San Francisco, giving it the somewhat = misleading appellation of the "San = Francisco=20 earthquake" (fig. 6.7). = Shaking=20 damage, however, was equally severe in many other places along the fault = rupture. The=20 frequently quoted value of 700 deaths caused by the earthquake and fire is now believed to = underestimate the total = loss of=20 life by a factor of 3 or 4. Most of the fatalities occurred in San Francisco, and 189 were = reported=20 else­where.

At = almost=20 precisely 5:12 a.m. local time, a foreshock occurred with=20 sufficient force to be felt widely through­out the = San=20 Francisco Bay area. The great earthquake broke loose some 20 to 25 s = later, with an=20 epicenter near San Francisco = (Bolt, 1968;=20 Boore, 1977). Violent shocks punctuated the strong shaking, which = lasted some=20 45 to 60 s. The earthquake was felt from southern Oregon to south of Los Angeles and inland as far = as=20 central Nevada (fig. 6.6). The highest MMI's of VII to IX paralleled the = length of the rupture, = extending as=20 far as 80 km inland from the fault trace. One important = characteristic of=20 the shaking intensity noted in = Lawson's=20 (1908) report was the clear correlation of intensity with = underlying=20 geologic conditions. Areas = situated in=20 sediment-filled valleys sus­tained stronger shaking than nearby = bedrock sites,=20 and the strongest shaking = occurred=20 in areas where groundreclaimed from=20 San Francisco Bay failed in the earth­quake. Modern seismic-zonation = practice accounts=20 for the differences in = seismic=20 hazard posed by varying geologic conditions (see Borcherdt, 1975, and = Ziony,=20 1985, for analyses of the = San=20 Francisco Bay and Los Angeles regions, respectively).

The=20 characteristics and amount of surface fault slip in this = earthquake=20 varied to a remarkable degree along the length of the rupture. Peak = displacements=20 of 6 m were measured near Olema on = the Point=20 Reyes peninsula, where the surface trace of the rupture formed a sharp,=20 well-defined break (fig. = 6.8). In=20 contrast, the fault break was extremely difficult to recognize = along its=20 southern­most 90 km, where = the surface=20 offset averaged only about P/2 m or=20 less (see chap. 7).

The = magnitude of=20 8.3 commonly quoted for the 1906 earthquake comes=20 from Richter (1958) and, within the precision of=20 reporting, is identical to the 8V4 listed by Gutenberg and=20 Richter (1954). Table 6.1 also lists other magnitudes for=20 this earthquake, derived from recent analyses of both the same data = used by=20 Gutenberg and Richter and new = data. Strictly=20 speaking, a "Richter magnitude"=20 (ML) for the earthquake cannot be = deter­mined because no appropriate = seismographs were=20 in

operation at the=20 time. Jennings and Kanamori (1979) used related measurements extracted = from simple=20 pendulums at Yountville, Calif., and Carson City, Nev., to derive ML=3D6.9, substantially = smaller than the=20 traditionally quoted value. ML, which is based = on the=20 single largest peak on a seismogram at approximately 1-s period and = takes into account neither the duration = of the=20 event nor longer period = motions, is=20 saturated for this event.

Geller = and=20 Kanamori (1977) used the unpublished worksheets of=20 Gutenberg and Richter to compute a body-wave=20 magnitude of mb=3D7A, using the procedure of = Gutenberg and=20 Richter (1956). Because long-period (14 s) P-waves = were used=20 in this calculation, it cannot be directly = compared=20 to the short-period mb values routinely reported = today.

Other = workers since=20 Gutenberg and Richter have studied = the=20 long-period surface waves of the 1906 earth­quake = and=20 computed Ms values. Bolt (1968) confirmed an = Ms=20 of = about 8V4,=20 whereas Lienkaemper (1984) found Ms=3D 8.3 = from an=20 analysis of all the records collected by Reid (1910). Lienkaemper's magnitude = combined=20 data from both damped and = undamped=20 instruments, correcting each for=20 magnification at the appropriate period of motion. Abe (1988), who analyzed only the = undamped Milne=20 seismograms, obtained Ms=3D 7.8, using slightly = different=20 procedures and a systematic set = of=20 station-magnitude corrections. Also, the four damped seismometers = (all in=20 Europe) give Ms=3D8.1. Longer period (50-100 s) surface waves analyzed by Thatcher (1975) = indicate a=20 seismic moment of 4xl027 dyne-cm, equivalent to = M=3D7.7, in=20 agreement with the seismic = moment of=20 5xl027 dyne-cm obtained from geodetic data, thus giving = M=3D7.8=20 (Thatch­er and Lisowski, 1987). Finally, Toppozada and Parke = (1982) assigned an intensity magnitude = (M/) of=20 7.8 on the basis of the total area (48,000 km2) undergoing = shaking of=20 MMI VII or = higher.