Subject: Re: all the best for the new year From: ian ian@........... Date: Fri, 31 Dec 2004 20:23:27 +0000 Happy New Year too. The USGS said on the day of the disaster that they were aware of the in coming tsunamis before they hit but didn't know who to contact. So the problem is not one of detection - the usgs have that covered - but one of dissemination. There is no communication and warning network around the affected area. I've heard that they had considered one but nothing happened. I guess there will soon be one now. Here, needless to say, my detector was off at the time, so unfortunately I missed an important test of my new Lehman. Ian Smith Mark Robinson wrote: > Hi everybody, > > The phrase "rock my world" just went out of fashion. > > I wonder if there is any software about that can monitor a seismograph > signal, pick P and S arrivals, calculate magnitude, location, tsunami > threat level, tsunami time of arrival over a defined coastline map, > automatically consult and vote with other neighbouring stations on the > threat level, and flip a bit on a serial or parallel port if > everything is looking really ugly, perhaps morse code "TS" ? You know, > all the bells and whistles. > > My coding skills suck these days, but I'll contribute whatever I can > to such a project if it doesn't exist, and if anyone else wants to, > purely in my own interests, living as I do on seaside sand dunes on an > active part of the intersection of the pacific and australien plates. > > Enjoy your friendships in celebrating the New Year. > Mark Robinson > ------------- > 01 Jan 1853 The strongest known earthquake in the New Plymouth area. 6.5. > 01 Jan 1854 Sir James George Frazer, author and scholar, born. > 01 Jan 1867 First Chinese immigrants to NZ arrive at Hokitika. > 01 Jan 1897 Author E M Forster born. > 01 Jan 1950 Castro seizes power in Cuba, Batista flees. > 01 Jan 1984 Mimiwhangata Marine Park established. > 01 Jan 1991 Presidents Bush and Gorbachev condemn Iraqi conquest of > Kuwait in > New Year's messages. > > > There's a mainframe wrecker about 70km from here that sells > semiconductor relays for $NZ3 each. These are easy to drive off a port > pin. > __________________________________________________________ > > 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: all the best for the new year From: Mark Robinson mark.robinson@............... Date: Sat, 01 Jan 2005 13:49:37 +1300 ian wrote: > Happy New Year too. > > The USGS said on the day of the disaster that they were aware of the in > coming tsunamis before they hit but didn't know who to contact. So the > problem is not one of detection - the usgs have that covered - but one > of dissemination. Hi Ian, Agreed, the problem is dissemination and communication, and the top down structure which is constrained by diplomatic protocols is too slow to be affective for many people, including me, for local events. Devices such as those I propose could mitigate these delays and save many many lives in similar future events. For me, safety from a large tsunami is a 7 minute drive on empty roads, or an hour walking and running. The local fire siren going off withing a minute or so of the initiating tremblor could reduce the radius without warning immensely, especially compared to people working their way through a documented protocol with a telephone. Let alone the political ramifications for many states who do not enjoy good political relations with the USA. We have already seen the USGS public face restricted for strategic reasons in the aftermath of 11Sep2001. I note that Indonesia now expects their death toll to be in the vicinity of 400,000. http://www.bernama.com/bernama/v3/news_lite.php?id=111574 "KUALA LUMPUR, Dec 30 (Bernama) -- The death toll in Acheh, the region worst hit by last Sunday's tsunami, may exceed 400,000 as many affected areas could still not be reached for search and rescue operations, Indonesia's Ambassador to Malaysia Drs H. Rusdihardjo said Thursday. He said the estimate was based on air surveillance by Indonesian authorities who found no signs of life in places like Meulaboh, Pulau Simeulue and Tapak Tuan while several islands off the west coast of Sumatera had "disappeared". He said the latest death toll of more than 40,000 in Acheh and northern Sumatera did not take into account the figures from the other areas, especially in the west of the region. ...." regards all Mark __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: P & S Markers Location, WQ From: "Steve Jones" acme100@.............. Date: Sun, 2 Jan 2005 19:39:06 -0600 Hi Larry, I have a question re: Winquake, and the P&S Marker location. I recorded the 12/26/04 M9.0 event (along with everybody else) and the later 01/01/05 M6.5 event off Sumatra. On both of these, I cannot get the P & S marker locations on the record to align with the first arrival of the P and S waves at my location. For each event, Winquake does calculate the distance to my location from the epicenter at 15000+ Km. I am running the WQ version 2.9, if that info helps. I have very carefully checked my timing and event location data plugged into Winquake. Do you have any idea why the P & S calculation seems to be off? If need be, I can email the two event records to you for your examination. Thanks, Steve Jones Huntsville, Alabama __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: P & S Markers Location, WQ From: apsn apsn@........... Date: Sun, 02 Jan 2005 16:55:39 -0900 Steve, Check your TABLES menu and make sure that you use either the IASPEI or Teleseismic tables. Bob http://apsn.awcable.com At 04:39 PM 1/2/2005, you wrote: >Hi Larry, >I have a question re: Winquake, and the P&S Marker location. I recorded the >12/26/04 M9.0 event (along with everybody else) and the later 01/01/05 M6.5 >event off Sumatra. On both of these, I cannot get the P & S marker >locations on the record to align with the first arrival of the P and S waves >at my location. For each event, Winquake does calculate the distance to my >location from the epicenter at 15000+ Km. > >I am running the WQ version 2.9, if that info helps. I have very carefully >checked my timing and event location data plugged into Winquake. Do you >have any idea why the P & S calculation seems to be off? > >If need be, I can email the two event records to you for your examination. > >Thanks, >Steve Jones >Huntsville, Alabama > >__________________________________________________________ > >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: P & S Markers Location, WQ From: "Larry Cochrane" lcochrane@.............. Date: Sun, 2 Jan 2005 20:09:26 -0800 Happy New Year Everyone, Hi Steve, You won't see a P or S wave after ~11000 km. This is because the earths core creates a shadow of the P wave and the outer core a shadow of the S wave. If you do a google search you can find more information. This page as a nice image showing what going on with the P and S waves. The IAPS91 travel-time table has information that goes past 11000km so WinQuake will place the P and S marks in the window, but they are meaningless do to the shadowing effect. Regards, Larry Cochrane Redwood City, PSN ----- Original Message ----- From: "Steve Jones" To: Sent: Sunday, January 02, 2005 5:39 PM Subject: P & S Markers Location, WQ > Hi Larry, > I have a question re: Winquake, and the P&S Marker location. I recorded the > 12/26/04 M9.0 event (along with everybody else) and the later 01/01/05 M6.5 > event off Sumatra. On both of these, I cannot get the P & S marker > locations on the record to align with the first arrival of the P and S waves > at my location. For each event, Winquake does calculate the distance to my > location from the epicenter at 15000+ Km. > > I am running the WQ version 2.9, if that info helps. I have very carefully > checked my timing and event location data plugged into Winquake. Do you > have any idea why the P & S calculation seems to be off? > > If need be, I can email the two event records to you for your examination. > > Thanks, > Steve Jones > Huntsville, Alabama > > __________________________________________________________ > > 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: P & S Markers Location, WQ From: John or Jan Lahr JohnJan@........ Date: Sun, 02 Jan 2005 22:37:36 -0700 Hi Steve,

You can use the calculator on this page:
http://neic.usgs.gov/neis/travel_times/artim.html
to find the time of arrival of all of the phases at your station. 

Cheers,
John

\At 09:09 PM 1/2/2005, you wrote:
Happy New Year Everyone,

Hi Steve,

You won't see a P or S wave after ~11000 km. This is because the earths core
creates a shadow of the P wave and the outer core a shadow of the S wave. If
you do a google search you can find more information. This page as a nice
image showing what going on with the P and S waves. The IAPS91 travel-time
table has information that goes past 11000km so WinQuake will place the P
and S marks in the window, but they are meaningless do to the shadowing
effect.

Regards,
Larry Cochrane
Redwood City, PSN


##################################/ John C. Lahr
#################################/ Emeritus Seismologist
################################/ U.S. Geological Survey
===========================/ Geologic Hazards Team, MS966
##############################/ PO Box 25046
#############################//##############################
############################//###############################
     Denver, Colorado 80225-0046 /################################
             Phone: (303) 215-9913 /=============================
               Fax: (303) 273-8540 /##################################
                     lahr@........ /###################################
                                          /####################################
                                 http://jclahr.com/science/
 Subject: Accelerometer on ebay From: "Edward Ianni" edwianni1@........... Date: Mon, 3 Jan 2005 21:29:39 -0500 Accelerometer ebay 3864167120 Ed Ianni

Accelerometer        &nb= sp; ebay=20 3864167120
 
Ed Ianni
Subject: Re; Accelerometers From: "Edward Ianni" edwianni1@........... Date: Tue, 4 Jan 2005 00:14:57 -0500 The link below may be useful in reference to accelerometers. The message is ready to be sent with the following file or link = attachments: Shortcut to: = http://www.civil.canterbury.ac.nz/eq/cusp1_04presentation.pdf =20 Ed Ianni
The link below may be useful in = reference to=20 accelerometers.
 
The=20 message is ready to be sent with the following file or link=20 attachments:
Shortcut to: http://www.civil.canterbury.ac.nz/eq/cusp1_04presentation.pdf
 
Ed = Ianni
Subject: Re: Accelerometer on ebay From: BOB BARNS royb1@........... Date: Tue, 04 Jan 2005 09:58:57 -0500 Hi Ed, This is a 3-pen chart recorder only, I think. It would prob. take 1V signals from seismic sensors for full scale. It would be hard to find chart paper and ink. Chart recording has gone out of style since computers can do so much more. OK on the accelerometer article. Bob Edward Ianni wrote: > Accelerometer ebay 3864167120 > > Ed Ianni > > > __________ NOD32 1.963 (20050103) Information __________ > > This message was checked by NOD32 antivirus system. > http://www.nod32.com __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: looking for a seismograph From: "David Saum" DSaum@............ Date: Tue, 4 Jan 2005 11:31:17 -0500 I received this message today and it is not something I know anything about. I hope there is someone on the list who can answer this question. -- Dave ----- Original Message ----- From: To: Sent: Tuesday, January 04, 2005 2:44 AM Subject: looking for a seismograph Dear Collegues, Your ewb infiltec.com is very interesting for me. I am looking for a seismograph equipment I hope You may help me to fine dealer and spec of equipment. I will be much appreciate if you could directs me to a dealer. I am looking for Drum type earthquake recorder which capable for detect quake from long distant i,e, should not be a strong motion equipment. Best regards Tun Aye __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: looking for a seismograph From: John or Jan Lahr JohnJan@........ Date: Tue, 04 Jan 2005 10:41:25 -0700 Dear Tun Aye,

Today very few seismic stations are recorded on a drum recorder.  The
expense of the drum and paper, combined with the daily chore of
changing the paper make this technique much less desirable than
recording digitally with a PC computer.  Also, with digital recording
one can adjust the time and amplitude scales as well as the filter
settings after an earthquake has been recorded.  This is especially 
helpful  in making measurements.

One option that is quite easy to set up would be to purchase an
AS1 instrument for $550.00.  In addition to the instrument you would
need a PC computer running MSWindows and the free software
AmaSeis, which can be downloaded from the web.

There is information on this approach posted here:
http://jclahr.com/science/psn/as1/

Some current records from schools are posted here:
http://jclahr.com/science/psn/as1/heli/allas1.php

Records of the recent M 9.0 Sumatra event are here:
http://jclahr.com/science/psn/as1/indonesia04/as1indo.html

*****
On the other hand, if you want to build your own system, there
is lots of information on the PSN web site:
http://psn.quake.net/

and here:
http://jclahr.com/science/psn/epics/links.html

Best of luck with your seismic recording.
John

At 09:31 AM 1/4/2005, you wrote:
I received this message today
and it is not something I know
anything about.
I hope there is someone
on the list who can answer
this question.  -- Dave

----- Original Message -----
From: <info-dmh@..........>
To: <dsaum@............>
Sent: Tuesday, January 04, 2005 2:44 AM
Subject: looking for a seismograph


Dear Collegues,

Your ewb infiltec.com is very interesting
for me.
I am looking for a seismograph equipment
I hope You may help me to fine
dealer and spec of equipment.

I will be much appreciate if you
could directs me  to a dealer.

I am looking for
 Drum type earthquake recorder
     which capable for detect quake from long distant
     i,e, should not be a strong motion equipment.

Best regards

Tun Aye
__________________________________________________________

Public Seismic Network Mailing List (PSN-L)

http://www.seismicnet.com/maillist.html for more information.


##################################/ John C. Lahr
#################################/ Emeritus Seismologist
################################/ U.S. Geological Survey
===========================/ Geologic Hazards Team, MS966
##############################/ PO Box 25046
#############################//##############################
############################//###############################
     Denver, Colorado 80225-0046 /################################
             Phone: (303) 215-9913 /=============================
               Fax: (303) 273-8540 /##################################
                     lahr@........ /###################################
                                          /####################################
                                 http://jclahr.com/science/
 Subject: Re: Simple mini horizontal From: John or Jan Lahr JohnJan@........ Date: Tue, 04 Jan 2005 11:09:47 -0700 Hi Ted, I'm curious how your recording is going? Did you catch the M 9 Sumatra event? I'm working with some students that the Colorado School of Mines who are interested in photo detection. Would you be willing to share your electronic circuit with them? I've been recommending using one light source and two detectors arranged so that when a flag is centered, both sensors are equally illuminated. Any movement increases the light to one and decreases it to the other. Since the output of interest is the difference between the two sensors, slight variations in the brightness of the light will not cause a false signal. Cheers, John At 03:52 PM 4/7/2004, you wrote: >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) > >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: source of L15B geophones From: "Thomas Dick" dickthomas01@............. Date: Tue, 4 Jan 2005 12:19:43 -0600 Any one know where I could get some of these geophones? __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Off-scale Waveforms From: "Timothy Carpenter" GeoDynamics@....... Date: Tue, 4 Jan 2005 14:31:44 -0500 All, =20 Please pardon me if this winds up a double posting =96 I'm still trying = to get e-mail addresses straightened out. =20 In the normal course of my work I've occasionally run across the problem = of vibration sensors being pushed beyond their physical limits =96 i.e; the suspended mass hits the end stops. For the most part, this has never = been a significant problem for me because there's always been another way to = get the data. However, when I downloaded seismic waveforms for the Dec 26th = EQ from Wooster, Ohio and Ann Arbor, Mi I found that their data had been compromised. It appears that the seismometers hit their stops and badly affected about 2-hours of the recordings. I believe this is the case at several of the stations but certainly not all of them. I found many = intact waveforms on the PSN server. =20 I've searched through my personal references as well as exercising = Google; but to no avail. So, I turn to the vast expertise of PSN. Are any of you aware of a numerical process by which such signals can be reliably = "fixed"? I'm sure that a neural network could be trained to approximate the true signal. But I'm more interested in a dynamic model consisting of a mass-spring-dashpot model of the seismometer and a spring-dashpot model = for the stops at the end of travel. =20 Regards, -Tim- =20 Timothy Carpenter, P.E., Pres., GeoDynamics Consultants, Inc. 5043 Whitlow Ct. Commerce Twp., Mi 48382 248-363-4529 (voice & fax) 248-766-1629 (cell) geodynamics@........... (primary) geodynamics@....... (secondary) =20 =20

All,

 

Please pardon me if this winds up a double posting = – I'm still trying to get e-mail addresses straightened out.

 

In the normal course of my work I've occasionally run = across the problem of vibration sensors being pushed beyond their physical = limits – i.e; the suspended mass hits the end stops. For the most part, = this has never been a significant problem for me because there's always been = another way to get the data. However, when I downloaded seismic waveforms for the = Dec 26th EQ from Wooster, Ohio and Ann = Arbor, Mi I found that their data had been compromised. It appears that the seismometers = hit their stops and badly affected about 2-hours of the recordings. I = believe this is the case at several of the stations but certainly not all of them. I = found many intact waveforms on the PSN server.

 

I've searched through my personal references as well = as exercising Google; but to no avail. So, I turn to the vast expertise of = PSN. Are any of you aware of a numerical process by which such signals can be reliably "fixed"? I'm sure that a neural network could be = trained to approximate the true signal. But I'm more interested in a dynamic model consisting of a mass-spring-dashpot model of the seismometer and a spring-dashpot model for the stops at the end of = travel.

 

Regards,

-Tim-

 

Timothy Carpenter, P.E., Pres.,
GeoDynamics Consultants, Inc.
5043 Whitlow Ct.
Commerce Twp., Mi 48382
248-363-4529 (voice & fax)
248-766-1629 (cell)
geodynamics@........... = (primary)
geodynamics@....... = (secondary)

 

 

Subject: RE: source of L15B geophones From: "Doug Crice" dcrice@............ Date: Tue, 4 Jan 2005 11:55:58 -0800 L15B geophones are made by Mark Products, but the last time I looked, = they had a substantial minimum charge. Mark was acquired by Sercel and their = web site is here http://www.sercel.com/Products/frproduct2.htm under = sensors, though I don't see the L15 listed, they may be available. You might find some used ones at R. T. Clark http://www.rtclark.com/ a purveyor of used geophysical hardware. However, if you are building a seismograph, you would be a lot better = off with Larry's 3-component 4.5 Hz geophones http://psn.quake.net/geophone/index.html Doug Crice Wireless Seismic http://www.wirelessSeismic.com 12996 Somerset Drive phone 1-530-274-4445 Grass Valley, CA 95945 USA fax 1-530-274-4446 =20 -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of Thomas Dick Sent: Tuesday, January 04, 2005 10:20 AM To: psn-l@.............. Subject: source of L15B geophones Any one know where I could get some of these geophones? __________________________________________________________ __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: source of L15B geophones From: Angel sismos@.............. Date: Tue, 4 Jan 2005 13:26:14 +0000 Hi, The geophones in Larry's 3c boxes are L15's Angel __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Ebay: "Proof Mass Actuator Earthquake Machine" From: "Meredith Lamb" meredithlamb@............. Date: Wed, 5 Jan 2005 12:48:30 -0700 Hi all, This "could/might be" a potential seismic sensing very short period or strong motion vertical sensor conversion item. Originally, its a "shake table actuator". The seller states outright that this is NOT a seismometer. The ~5 kilogram mass has both a piezo sensor and a LDVT (linear differential variable transformer). The mass ( presumed to be either iron or a magnet?) is driven like a speaker voice coil windings around the outside of the mass. Seven inch diameter by one foot high item....but unknown total weight. The bell shaped exterior item picture, makes it look very sturdy and solid as is. On the other hand....the item could be worthless as is, or in any conversion attempt. Its (?) possible, that the metal shell alone might be worth the cost for any other derived seismometer enclosure scheme. In ways....I wonder if the piezo and LDVT were "somehow" mechanically disconnected, that the original wire coil power driven input; could then be a functional magnetic induction output velocity signal source....or....as a feedback or dampening medium? Of course, either the piezo or LDVT could be entertained also,..... but their mechanical coupling might be a motion sensing hinderance. The seller is offering a quanity of ~5 "buy it now" ($74.67), and seven other starting bid ($64.67) items. See E-Bay item #'s, 2596230058 and 3865011737, for a picture and more info. Take care, Meredith Lamb

Hi all,
 
This "could/might be" a potential seismic sensing very short period or strong motion
vertical sensor conversion item.  Originally, its a "shake table actuator".  The seller states
outright that this is NOT a seismometer.  The ~5 kilogram mass has both a piezo sensor and
a LDVT (linear differential variable transformer).  The mass ( presumed to be either iron or
a magnet?) is driven like a speaker voice coil windings around the outside of the mass. 
Seven inch diameter by one foot high item....but unknown total weight.  The bell shaped
exterior item picture, makes it look very sturdy and solid as is.  On the other hand....the item
could be worthless as is, or in any conversion attempt.   Its (?) possible, that the metal shell
alone might be worth the cost for any other derived seismometer enclosure scheme.
 
In ways....I wonder if the piezo and LDVT were "somehow" mechanically disconnected, that
the original wire coil power driven input; could then be a functional magnetic induction output
velocity signal source....or....as a feedback or dampening medium?  Of course, either the
piezo or LDVT could be entertained also,..... but their mechanical coupling might be a
motion sensing hinderance. 
 
The seller is offering a quanity of ~5 "buy it now" ($74.67), and seven other starting bid
($64.67) items.  See E-Bay item #'s, 2596230058 and 3865011737, for a picture and more info. 
 
Take care, Meredith Lamb
 
 

Subject: SDR Board For Sale From: "Rex Klopfenstein, Jr." rklopfen@......... Date: Wed, 5 Jan 2005 21:26:35 -0500 All I have just ordered a new serial SDR card so I am selling my DOS SDR card on EBay. Do a search with seismic and you should find. Thanks Rex Klopfenstein Bowling Green, OH

All

I have just ordered a new serial SDR card so I am = selling my DOS SDR card on EBay.  Do a = search with seismic and you should find.

Thanks


Rex Klopfenstein

Bowling Green, OH

Subject: Surface waves from Sumatra M 9.0 From: John or Jan Lahr JohnJan@........ Date: Thu, 06 Jan 2005 07:41:27 -0700 If you haven't taken a look at the IRIS "Image of the Week" yet, check out this page: file:///C:/education/Sumatra%209.0/surface_waves.htm The image shows seismic records from stations distributed around the globe and surface waves that traveled twice around! Questions to think about -- Why does the y-axis stop at 180 degrees? Why would the amplitude of the surface waves fall off around 90 degrees and then increase at 180 degrees again? Cheers, John __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Surface waves from Sumatra M 9.0 From: "Larry P Thomas" lpthomas@......... Date: Thu, 6 Jan 2005 10:18:11 -0600 John, Your link points to a file which is local on your hard drive and I can't, of course, pull that up with my browser. Does it exist on the web someplace? file:///C:/education/Sumatra%209.0/surface_waves.htm Thanks, Larry P. Thomas, wa0gwa Imagine it/Achieve it --- Dream it/Become it Larry P. Thomas, wa0gwa 1 913 244-8761 Krell Technologies (http://www.krell.com) 8960 Bond, Overland Park, KS 66214-1722 USA __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Surface waves from Sumatra M 9.0 From: Bob Hancock Bob_Hancock@............ Date: Thu, 06 Jan 2005 09:27:36 -0700 This link works..... http://dmc.iris.washington.edu/about/ENO/iow.htm -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Larry P Thomas Sent: Thursday, January 06, 2005 09:18 To: psn-l@.............. Subject: RE: Surface waves from Sumatra M 9.0 John, Your link points to a file which is local on your hard drive and I can't, of course, pull that up with my browser. Does it exist on the web someplace? file:///C:/education/Sumatra%209.0/surface_waves.htm Thanks, Larry P. Thomas, wa0gwa Imagine it/Achieve it --- Dream it/Become it Larry P. Thomas, wa0gwa 1 913 244-8761 Krell Technologies (http://www.krell.com) 8960 Bond, Overland Park, KS 66214-1722 USA __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Surface waves from Sumatra M 9.0 From: "Thomas Dick" dickthomas01@............. Date: Thu, 6 Jan 2005 11:02:46 -0600 type in iris image of the week -- your browser should show it as the first or second option > __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Surface waves from Sumatra M 9.0, 2nd Version From: John or Jan Lahr JohnJan@........ Date: Thu, 06 Jan 2005 12:10:20 -0700 If you haven't taken a look at the IRIS "Image of the Week" yet, check out this page (with the now correct URL!): http://www.iris.edu/about/ENO/iow.htm The image shows seismic records from stations distributed around the globe and surface waves that traveled twice around! Questions to think about -- Why does the y-axis stop at 180 degrees? Why would the amplitude of the surface waves fall off around 90 degrees and then increase at 180 degrees again? Cheers, John __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Surface waves from Sumatra M 9.0, 2nd Version From: "twleiper@......... twleiper@juno.com Date: Thu, 6 Jan 2005 19:37:47 GMT I would suspect destructive interference of the wave fronts at the quarter-wave point (50 minutes) assuming the resonance of the "global tank circuit" is 200 minutes. Either that or some type of phase shift. How about the coriolis effect ? :-) -- John or Jan Lahr wrote: If you haven't taken a look at the IRIS "Image of the Week" yet, check out this page (with the now correct URL!): http://www.iris.edu/about/ENO/iow.htm The image shows seismic records from stations distributed around the globe and surface waves that traveled twice around! Questions to think about -- Why does the y-axis stop at 180 degrees? Why would the amplitude of the surface waves fall off around 90 degrees and then increase at 180 degrees again? Cheers, John __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Surface waves from Sumatra M 9.0, 2nd Version From: John Hernlund hernlund@............ Date: Thu, 6 Jan 2005 13:48:16 -0800 John, Thanks for pointing this out. Hint for answer: Earth is spherical, not circular... Cheers! John On Thursday, January 6, 2005, at 11:10 AM, John or Jan Lahr wrote: > If you haven't taken a look at the IRIS "Image of the Week" yet, > check out this page (with the now correct URL!): > http://www.iris.edu/about/ENO/iow.htm > > The image shows seismic records from stations distributed around > the globe and surface waves that traveled twice around! > > Questions to think about -- Why does the y-axis stop at 180 degrees? > Why would the amplitude of the surface waves fall off around 90 degrees > and then increase at 180 degrees again? > > Cheers, > John > > __________________________________________________________ > > 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: Surface waves from Sumatra M 9.0, 2nd Version From: Jack Ivey ivey@.......... Date: Thu, 6 Jan 2005 17:02:06 -0500 Ok, I'll bite. The wave front is always a circle, but the size of the circle varies. Near the source, it is a small circle and the energy is concentrated. At 90 degrees, it is a large (great) circle, the same diameter as the earth, spreading the energy out. At the antipodes, the circle shrinks again, concentrating the energy. This causes the blip in amplitude at angles near 180. The wave is also dissipating energy and dispersing, so the blip is superimposed on an overall decreasing amplitude. The same thing happens with VLF radio transmissions traveling around the globe. Jack On Thursday, January 6, 2005, at 11:10 AM, John or Jan Lahr wrote: > If you haven't taken a look at the IRIS "Image of the Week" yet, > check out this page (with the now correct URL!): > http://www.iris.edu/about/ENO/iow.htm > > The image shows seismic records from stations distributed around > the globe and surface waves that traveled twice around! > > Questions to think about -- Why does the y-axis stop at 180 degrees? > Why would the amplitude of the surface waves fall off around 90 degrees > and then increase at 180 degrees again? > > Cheers, > John > > __________________________________________________________ > > 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) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Surface waves from Sumatra M 9.0, 2nd Version From: Mark Robinson mark.robinson@............... Date: Fri, 07 Jan 2005 11:15:10 +1300 John Hernlund wrote: > John, > > Thanks for pointing this out. > > Hint for answer: Earth is spherical, not circular... > > Cheers! > John > > On Thursday, January 6, 2005, at 11:10 AM, John or Jan Lahr wrote: > >> If you haven't taken a look at the IRIS "Image of the Week" yet, >> check out this page (with the now correct URL!): >> http://www.iris.edu/about/ENO/iow.htm >> >> The image shows seismic records from stations distributed around >> the globe and surface waves that traveled twice around! >> >> Questions to think about -- Why does the y-axis stop at 180 degrees? >> Why would the amplitude of the surface waves fall off around 90 degrees >> and then increase at 180 degrees again? >> >> Cheers, >> John Hi folks, If you have access to a room with a dome, go there with a friend, take up positions on opposite sides, and whisper. Mark Robinson ------------- 07 Jan 1924 George Gershwin composes Rhapsody in Blue. 07 Jan 1952 Ike offers to accept GOP Presidential Nomination. __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Surface waves from Sumatra M 9.0, 2nd Version From: "Timothy Carpenter" GeoDynamics@....... Date: Thu, 6 Jan 2005 17:31:04 -0500 John, You asked a couple of questions after giving us the link to the Global Displacement Wavefield. I started to write up a quick answer, but since = I'm new to the group I thought I better find out a bit more about who was = asking the questions. I'm glad I did. I'll leave the questions unanswered for others to ponder. I presume after some reasonable amount of time, you = will provide the answers.=20 -Tim- Timothy Carpenter, P.E., Pres., GeoDynamics Consultants, Inc. 5043 Whitlow Ct. Commerce Twp., Mi 48382 248-363-4529 (voice & fax) 248-766-1629 (cell) geodynamics@........... (primary) geodynamics@....... (secondary) -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of twleiper@........ Sent: Thursday, January 06, 2005 2:38 PM To: psn-l@.............. Subject: Re: Surface waves from Sumatra M 9.0, 2nd Version I would suspect destructive interference of the wave fronts at the quarter-wave point (50 minutes) assuming the resonance of the "global tank circuit" is 200 minutes. Either that or some type of phase shift. How about the coriolis effect ? :-) -- John or Jan Lahr wrote: If you haven't taken a look at the IRIS "Image of the Week" yet, check out this page (with the now correct URL!): http://www.iris.edu/about/ENO/iow.htm The image shows seismic records from stations distributed around the globe and surface waves that traveled twice around! Questions to think about -- Why does the y-axis stop at 180 degrees? Why would the amplitude of the surface waves fall off around 90 degrees and then increase at 180 degrees again? Cheers, John=20 __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Global Simulation of Sumarta EQ From: "Timothy Carpenter" GeoDynamics@....... Date: Sat, 8 Jan 2005 05:07:41 -0500 This program provides an excellent representation of how seismic waves travel through and around the globe. http://www.geol.binghamton.edu/faculty/jones/jones.html Scroll down to: "Seismic Waves: A program for the visualization of wave propagation" Download seiswave.readme and SeismicWavesSetup.exe. Read the readme file and then Run the setup program. When the installation is finished, run the animation and select the Sumatra Quake. After it has finished with one quake, the program moves on to another. Regards, -Tim- Timothy Carpenter, P.E., Pres., GeoDynamics Consultants, Inc. 5043 Whitlow Ct. Commerce Twp., Mi 48382 248-363-4529 (voice & fax) 248-766-1629 (cell) geodynamics@........... (primary) geodynamics@....... (secondary)

This program = provides an excellent representation of how seismic waves travel through and around = the globe.

http://www.geol.binghamton.edu/facul= ty/jones/jones.html

Scroll down to: = "Seismic Waves: A program for the visualization of wave propagation"

Download seiswave.readme and SeismicWavesSetup.exe.

Read the readme file and then Run = the setup program= .

When the installation is finished, = run the animation and select the Sumatra Quake. After it has finished with one = quake, the program= moves on to another.

Regards,

-Tim-

Timothy Carpenter, P.E., Pres.,
GeoDynamics Consultants, Inc.
5043 Whitlow Ct.
Commerce Twp., Mi 48382
248-363-4529 (voice & fax)
248-766-1629 (cell)
geodynamics@........... = (primary)
geodynamics@....... = (secondary)

 

 

Subject: Iris Waveform Chart From: "Connie and Jim Lehman" lehmancj@........... Date: Sun, 9 Jan 2005 19:02:32 -0500 PSN--thanks for the Iris Waveform Chart for the 9.0 Sumatra 12/26/04 = event. The surface wave arrivals of multiple stations exhibited by = distance, and text, makes a super graphic. I was wondering about the = occurrence of a seismic caustic at the appropriate degree distance. Was = the gap at 160 degree area due to no reporting station near the = "caustic" distance. In periodic recording here we've copied three = caustics in 20 years--I believe the events were southwest of Australia = for us--not a very hot spot. The 18 sec long period system at James Madison Un. (Virginia) = working into a graphic readout read the 8.1 Macquarie Is. event-(l2/23) = nicely, but the 9.0 event read 20 min after P-diff arrived and then went = off scale for 100 minutes and returned to normal recording for the 7.1 = event at 04:21. One can conclude, surface wave arrivals for us (at = approx. 145 degrees) were obscured. Keep up the good work. Jim Lehman
PSN--thanks for the Iris Waveform Chart = for the=20 9.0 Sumatra  12/26/04 event.  The surface wave arrivals of = multiple=20 stations exhibited by distance, and text,  makes a super = graphic.  I=20 was wondering about  the occurrence of a seismic caustic at the = appropriate=20 degree distance.  Was the gap at 160 degree area due to no = reporting=20 station near the "caustic" distance.  In periodic recording here = we've=20 copied three caustics  in 20 years--I believe the events were = southwest of=20 Australia for us--not a very hot spot.
    The 18 sec long = period system=20 at James Madison Un.  (Virginia) working into a graphic readout = read the=20 8.1 Macquarie Is. event-(l2/23) nicely, but the 9.0 event read 20 min = after=20 P-diff arrived and then went off scale for 100 minutes and returned to = normal=20 recording for the 7.1 event at 04:21.  One can conclude, = surface wave=20 arrivals for us (at approx. 145 degrees) were obscured.  = Keep up=20 the good work.
          =  =20 Jim Lehman
Subject: ebay auction From: BOB BARNS royb1@........... Date: Sat, 15 Jan 2005 13:18:17 -0500 Hi gang, Vintage Seismoscope U-17 Earthquake Measurement Tool Item number: 6146607454 ends Jan. 20 Bob Barns __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: ebay auction From: BOB BARNS royb1@........... Date: Sat, 15 Jan 2005 13:20:08 -0500 Hi gang, I should have put both of these in one message, sorry. Nomis NCSC 5000 Seismograph Vibratech Item number: 6146573473 ends Jan 20 Bob Barns __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: ebay auction From: BOB BARNS royb1@........... Date: Mon, 24 Jan 2005 10:24:25 -0500 Another geophone-- WORKING SEISMOGRAPH SEISMIC GEOPHONE Item number: 6148741624 ends Jan. 29 Bob Barns __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: ebay auctions From: BOB BARNS royb1@........... Date: Mon, 31 Jan 2005 21:08:27 -0500 Wilmot SR-100 Seismoscope Earthquake Recorder Survey Type Strong-Motion Stainless-Steel Unit = Works! Item number: 6150616013 ends Feb 9 v. interesting! but not for New Jersey. ------------- WORKING SEISMOGRAPH SEISMIC GEOPHONE Item number: 6150843011 ends Feb 6 another geophone Bob Barns __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Helioseismology From: Bob Hancock Bob.Hancock@............ Date: Tue, 01 Feb 2005 09:09:02 -0700 Space Weather had an interesting article on helioseismology, or how they are using sound waves to map the interior of the sun. http://spaceweather.com Article on Heliseismic Holography http://spaceweather.com/glossary/farside.html Article on Helioseismology http://science.msfc.nasa.gov/ssl/pad/solar/p_modes.htm

Space Weather had an interesting article on helioseismology, or how they are using sound waves to map the interior of the sun.

 

http://spaceweather.com

 

Article on Heliseismic Holography

 

            http://spaceweather.com/glossary/farside.html

 

Article on Helioseismology

 

            http://science.msfc.nasa.gov/ssl/pad/solar/p_modes.htm

 

Subject: RE: Iris Waveform Chart From: "Timothy Carpenter" GeoDynamics@....... Date: Sat, 5 Feb 2005 16:33:00 -0500 I should probably know =96 but I don't. What is the "caustic" distance? = And for that matter, what is the "caustic"? Regards, -Tim- =20 Timothy Carpenter, P.E., Pres., GeoDynamics Consultants, Inc. 5043 Whitlow Ct. Commerce Twp., Mi 48382 248-363-4529 (voice & fax) 248-766-1629 (cell) geodynamics@........... (primary) geodynamics@....... (secondary) =20 =20 -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of Connie and Jim Lehman Sent: Sunday, January 09, 2005 7:03 PM To: psn-l@.............. Subject: Iris Waveform Chart =20 PSN--thanks for the Iris Waveform Chart for the 9.0 Sumatra 12/26/04 = event. The surface wave arrivals of multiple stations exhibited by distance, = and text, makes a super graphic. I was wondering about the occurrence of = a seismic caustic at the appropriate degree distance. Was the gap at 160 degree area due to no reporting station near the "caustic" distance. In periodic recording here we've copied three caustics in 20 years--I = believe the events were southwest of Australia for us--not a very hot spot. The 18 sec long period system at James Madison Un. (Virginia) = working into a graphic readout read the 8.1 Macquarie Is. event-(l2/23) nicely, = but the 9.0 event read 20 min after P-diff arrived and then went off scale = for 100 minutes and returned to normal recording for the 7.1 event at 04:21. One can conclude, surface wave arrivals for us (at approx. 145 degrees) = were obscured. Keep up the good work. Jim Lehman

I should probably know – but = I don't. What is the "caustic" distance? And for that matter, = what is the "caustic"?

Regards,

-Tim-

 

Timothy = Carpenter, P.E., Pres.,
GeoDynamics Consultants, Inc.
5043 Whitlow Ct.
Commerce Twp., Mi 48382
248-363-4529 (voice & fax)
248-766-1629 (cell)
geodynamics@........... = (primary)
geodynamics@....... = (secondary)

 

 

-----Original = Message-----
From: = psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Connie and Jim Lehman
Sent: Sunday, January 09, = 2005 7:03 PM
To: = psn-l@..............
Subject: Iris Waveform = Chart

 

PSN--thanks for the Iris = Waveform Chart for the 9.0 Sumatra  12/26/04 event.  The surface wave = arrivals of multiple stations exhibited by distance, and text,  makes a = super graphic.  I was wondering about  the occurrence of a seismic = caustic at the appropriate degree distance.  Was the gap at 160 degree area = due to no reporting station near the "caustic" distance.  In = periodic recording here we've copied three caustics  in 20 years--I believe = the events were southwest of Australia for us--not a very hot = spot.

    The 18 = sec long period system at James Madison Un.  (Virginia) working into a = graphic readout read the 8.1 Macquarie Is. event-(l2/23) nicely, but the 9.0 = event read 20 min after P-diff arrived and then went off scale for 100 minutes and returned to normal recording for the 7.1 event at 04:21.  = One can conclude, surface wave arrivals for us (at approx. 145 = degrees) were obscured.  Keep up the good work.

    &nbs= p;       Jim Lehman

Subject: RE: Iris Waveform Chart From: "Jorma Kanninen" jorma@............. Date: Sat, 5 Feb 2005 23:34:31 +0000 Hi Tim, Now I'm getting a bit puzzled ! Cheers, Jorma From: psn-l-request@.............. [mailto:psn-l-request@webtroni= cs.com] On Behalf Of Timothy Carpenter Sent: 05 February 2005 21:33 To: psn-l@.............. Subject: RE: Iris Waveform Chart I should probably know =96 but I don't. What is the "caustic" dis= tance? And for that matter, what is the "caustic"? Regards, -Tim- Timothy Carpenter, P.E., Pres., GeoDynamics Consultants, Inc. 5043 Whitlow Ct. Commerce Twp., Mi 48382 248-363-4529 (voice & fax) 248-766-1629 (cell) geodynamics@........... (primary) geodynamics@....... (secondary) -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@webtroni= cs.com] On Behalf Of Connie and Jim Lehman Sent: Sunday, January 09, 2005 7:03 PM To: psn-l@.............. Subject: Iris Waveform Chart PSN--thanks for the Iris Waveform Chart for the 9.0 Sumatra 12/2= 6/04 event. The surface wave arrivals of multiple stations exhib= ited by distance, and text, makes a super graphic. I was wonder= ing about the occurrence of a seismic caustic at the appropriate= degree distance. Was the gap at 160 degree area due to no repor= ting station near the "caustic" distance. In periodic recording=20= here we've copied three caustics in 20 years--I believe the even= ts were southwest of Australia for us--not a very hot spot. The 18 sec long period system at James Madison Un. (Virginia= ) working into a graphic readout read the 8.1 Macquarie Is. event= -(l2/23) nicely, but the 9.0 event read 20 min after P-diff arriv= ed and then went off scale for 100 minutes and returned to normal= recording for the 7.1 event at 04:21. One can conclude, surface= wave arrivals for us (at approx. 145 degrees) were obscured. Ke= ep up the good work. Jim Lehman
Hi Tim,
 
Now I'm getting a bit puzzled !
 
Cheers,
 
Jorma

From: psn-l-request@webtronic= s.com [mailto:psn-l-request@............... On Behalf Of Timothy= Carpenter
Sent: 05 February 2005 21:33
To: psn-l@..............
Subject: RE: Iris Waveform Chart

I shou= ld probably know – but I don't. What is the "caustic" distance? And for that= matter, what is the "caustic"?

Regard= s,

-Tim-

 

Timothy Carpenter, P.E., Pres.,
GeoDyn= amics Consultants, Inc.
5043 Whitlow Ct.
Commerce Twp., Mi 48382
248-363-45= 29 (voice & fax)
248-766-1629 (cell)
geodynamics@........... (primary)
geodynamics@a= tt.net (secondary)

 

 

-----Original Message-----
From:= psn-l-request@.............. [mailto:psn-l-request@............... ] On Behalf Of Connie and Ji= m Lehman
Sent: S= unday, January 09, 2005 7:03 PM
To: psn-l@..............
Subj= ect: Iris Waveform Chart

 

=

PSN-= -thanks for the Iris Waveform Chart for the 9.0 Sumatra  12/26/04 event.&nbs= p; The surface wave arrivals of multiple stations exhibited by distance, and tex= t,  makes a super graphic.  I was wondering about  the occurrence= of a seismic caustic at the appropriate degree distance.  Was the gap at=20= 160 degree area due to no reporting station near the "caustic" distance.  In= periodic recording here we've copied three caustics  in 20 years--I b= elieve the events were southwest of Australia for us--not a very hot spot.

&nbs= p;   The 18 sec long period system at James Madison Un.  (Virginia) w= orking into a graphic readout read the 8.1 Macquarie Is. event-(l2/23) nicely,=20= but the 9.0 event read 20 min after P-diff arrived and then went off scale fo= r 100 minutes and returned to normal recording for the 7.1 event at 04:21. = ; One can conclude, surface wave arrivals for us (at approx. 145 degre= es) were obscured.  Keep up the good work.=

   &= nbsp;        Jim Lehman

Subject: RE: Iris Waveform Chart From: "Jorma Kanninen" jorma@............. Date: Sat, 5 Feb 2005 23:42:20 +0000 FYI The line caustic behavior has been discussed since Chang and Refs= dal (1979) mentioned inverse-square-root-of-the-distance dependen= ce of the amplification of the images near the critical curve in=20= a study of a single point mass under the influence of a constant=20= shear due to a larger mass. A quarter century later, Gaudi and Pe= tters (2001) interprets that the distance is {\it a vertical dist= ance to the caustic}. It is an erroneous misinterpretation. We rehash Rhie and Bennett (1999) where the caustic behavior of t= he binary lenses was derived to study the feasibility of limb dar= kening measurements in caustic crossing microlensing events. ~({\= it 1}) $J =3D \pm \sqrt{4\delta\omega_{2-} J_-}$ where ~$\delta\o= mega\parallel\bar\partial J$, and $\delta\omega_{2-}$ and $J_-$ a= re $E_-$-components of $\delta\omega$ (the source position shift=20= from the caustic curve) and $2\bar\partial J$ (the gradient of th= e Jacobian determinant) respectively; ~({\it 2}) The critical eig= envector $\pm E_-$ is normal to the caustic curve and easily dete= rmined from the analytic function $\kappa$-field; ~({\it 3}) Near= a cusp ($J_- =3D 0$) is of a behavior of the third order, and th= e direction of $\bar\partial J$ with respect to the caustic curve= changes rapidly because a cusp is an accumulation point; ~({\it=20= 4}) On a planetary caustic, $|\partial J|\sim \sqrt{1/\epsilon_{p= l}}$ is large and power expansion does not necessarily converge o= ver the size of the lensed star. In practice, direct numerical su= mmation is inevitable. We also note that a lens equation with constant shear is intrinsi= cally incomplete and requires supplementary physical assumptions=20= and interpretations in order to be a viable model for a lensing s= ystem. Cheers, Jorma ________________________________ From: psn-l-request@.............. [mailto:psn-l-request@webtroni= cs.com] On Behalf Of Timothy Carpenter Sent: 05 February 2005 21:33 To: psn-l@.............. Subject: RE: Iris Waveform Chart I should probably know =E2=80=93 but I don't. What is the "causti= c" distance? And for that matter, what is the "caustic"? Regards, -Tim- Timothy Carpenter, P.E., Pres., GeoDynamics Consultants, Inc. 5043 Whitlow Ct. Commerce Twp., Mi 48382 248-363-4529 (voice & fax) 248-766-1629 (cell) geodynamics@........... (primary) geodynamics@....... (secondary) -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@webtroni= cs.com] On Behalf Of Connie and Jim Lehman Sent: Sunday, January 09, 2005 7:03 PM To: psn-l@.............. Subject: Iris Waveform Chart PSN--thanks for the Iris Waveform Chart for the 9.0 Sumatra 12/2= 6/04 event. The surface wave arrivals of multiple stations exhib= ited by distance, and text, makes a super graphic. I was wonder= ing about the occurrence of a seismic caustic at the appropriate= degree distance. Was the gap at 160 degree area due to no repor= ting station near the "caustic" distance. In periodic recording=20= here we've copied three caustics in 20 years--I believe the even= ts were southwest of Australia for us--not a very hot spot. The 18 sec long period system at James Madison Un. (Virginia= ) working into a graphic readout read the 8.1 Macquarie Is. event= -(l2/23) nicely, but the 9.0 event read 20 min after P-diff arriv= ed and then went off scale for 100 minutes and returned to normal= recording for the 7.1 event at 04:21. One can conclude, surface= wave arrivals for us (at approx. 145 degrees) were obscured. Ke= ep up the good work. Jim Lehman __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Iris Waveform Chart From: John or Jan Lahr johnjan@........ Date: Sat, 05 Feb 2005 18:06:53 -0800 Caustic. An earthquake sends waves out in all directions. In ray theory, one=20 considers just one "ray" at a time. A ray that starts out going horizontally will soon reach= =20 the surface of the earth, where as a ray that starts out going directly downward will go=20 straight through the Earth and reach the "other side of the Earth" at a distance of 180=20 degrees ( the angular distance as measured from the center of the Earth). If we consider an ray= =20 leaving the earthquake source in the horizontal direction to have a "take-off" angle of= =20 zero, while a ray going straight down has a take-off angle of 90, then, in general, the=20 greater the take off angle of the ray, the greater the distance the ray emerges. However, due to the changes in velocity of the Earth with depth, most= notably the decrease in P-wave velocity in the outer core as compared to the lower= =20 mantle, there are some distances where, as the take off angle increases the distance=20 where the ray emerges starts to DECREASE! At these points, called caustics, there=20 is a focusing effect leading to higher amplitude waves being observed. I'm sure others will add to this! Cheers, John At 03:34 PM 2/5/2005, you wrote: >Hi Tim, > >Now I'm getting a bit puzzled ! > >Cheers, > >Jorma > > >---------- >From: psn-l-request@.............. [mailto:psn-l-request@.................. >On Behalf Of Timothy Carpenter >Sent: 05 February 2005 21:33 >To: psn-l@.............. >Subject: RE: Iris Waveform Chart > >I should probably know =96 but I don't. What is the "caustic" distance? And= =20 >for that matter, what is the "caustic"? > >Regards, > >-Tim- > > > >Timothy Carpenter, P.E., Pres., >GeoDynamics Consultants, Inc. >5043 Whitlow Ct. >Commerce Twp., Mi 48382 >248-363-4529 (voice & fax) >248-766-1629 (cell) >geodynamics@........... (primary) >geodynamics@....... (secondary) > > > > > >-----Original Message----- >From: psn-l-request@.............. [mailto:psn-l-request@.................. >On Behalf Of Connie and Jim Lehman >Sent: Sunday, January 09, 2005 7:03 PM >To: psn-l@.............. >Subject: Iris Waveform Chart > > > >PSN--thanks for the Iris Waveform Chart for the 9.0 Sumatra 12/26/04=20 >event. The surface wave arrivals of multiple stations exhibited by=20 >distance, and text, makes a super graphic. I was wondering about the=20 >occurrence of a seismic caustic at the appropriate degree distance. Was=20 >the gap at 160 degree area due to no reporting station near the "caustic"= =20 >distance. In periodic recording here we've copied three caustics in 20=20 >years--I believe the events were southwest of Australia for us--not a very= =20 >hot spot. > > The 18 sec long period system at James Madison Un. (Virginia)=20 > working into a graphic readout read the 8.1 Macquarie Is. event-(l2/23)=20 > nicely, but the 9.0 event read 20 min after P-diff arrived and then went= =20 > off scale for 100 minutes and returned to normal recording for the 7.1=20 > event at 04:21. One can conclude, surface wave arrivals for us (at=20 > approx. 145 degrees) were obscured. Keep up the good work. > > Jim Lehman __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: Re: Iris Waveform Chart From: "Connie and Jim Lehman" lehmancj@........... Date: Sun, 6 Feb 2005 18:17:50 -0500 Tim & others- According to Bath, Intro. to Seismology, the author explains a seismic = caustic as follows. In a model of Earth with Core 1/2 dia. of the Earth = Sphere, and a ratio of density l:1.2, every point situated more than 155 = degrees from the surface event will receive not one but two PKP waves = which propigate along different paths. Exactly at 155 degrees, these = waves coincide and result in a great concentration of energy--or a = Caustic. =20 For reasons not easily explained, this caustic --in real earth = seismicity occurs at or near 144 degrees. The net effect of the Caustic = is a ring of PKP concentration 36 degrees away from the "antipode" of = the event. ( Remember direct P-waves observe quiet time from 103 to 144 = degrees ) Although I have never seen this demo, I understand a sphere of high = density glass enclosed with a sphere of lower density glass will show a = similar ring of lazer light entering the far side. Of course acoustic = caustics can be demonstrated. The few caustics noted here (long Period) have a signature very = unique from the usual events of S. Pacific. The front loading of P = related waves are larger than any of the other wave fronts, expecially = in deep events where surface waves are minimized. No doubt there are better explanations (Thanks Jorma) of this = seismic phenomenon. Do the geometry of P energy through the Core, and = one gets an idea of what is going on. Jim Lehman ----- Original Message -----=20 From: Timothy Carpenter=20 To: psn-l@................. Sent: Saturday, February 05, 2005 4:33 PM Subject: RE: Iris Waveform Chart I should probably know - but I don't. What is the "caustic" distance? = And for that matter, what is the "caustic"? Regards, -Tim- Timothy Carpenter, P.E., Pres., GeoDynamics Consultants, Inc. 5043 Whitlow Ct. Commerce Twp., Mi 48382 248-363-4529 (voice & fax) 248-766-1629 (cell) geodynamics@........... (primary) geodynamics@....... (secondary) -----Original Message----- From: psn-l-request@.............. = [mailto:psn-l-request@............... On Behalf Of Connie and Jim Lehman Sent: Sunday, January 09, 2005 7:03 PM To: psn-l@.............. Subject: Iris Waveform Chart PSN--thanks for the Iris Waveform Chart for the 9.0 Sumatra 12/26/04 = event. The surface wave arrivals of multiple stations exhibited by = distance, and text, makes a super graphic. I was wondering about the = occurrence of a seismic caustic at the appropriate degree distance. Was = the gap at 160 degree area due to no reporting station near the = "caustic" distance. In periodic recording here we've copied three = caustics in 20 years--I believe the events were southwest of Australia = for us--not a very hot spot. The 18 sec long period system at James Madison Un. (Virginia) = working into a graphic readout read the 8.1 Macquarie Is. event-(l2/23) = nicely, but the 9.0 event read 20 min after P-diff arrived and then went = off scale for 100 minutes and returned to normal recording for the 7.1 = event at 04:21. One can conclude, surface wave arrivals for us (at = approx. 145 degrees) were obscured. Keep up the good work. Jim Lehman
Tim & others-
 
According to Bath, Intro. to=20 Seismology, the author explains a seismic caustic as = follows.  In=20 a model of Earth with Core 1/2 dia. of the Earth Sphere, and a ratio of = density=20 l:1.2, every point situated more than 155 degrees from the surface event = will=20 receive not one but two PKP waves which propigate along different=20 paths.  Exactly at 155 degrees, these waves coincide and result in = a great=20 concentration of energy--or a Caustic. 
   For reasons not easily = explained,=20 this caustic --in real earth seismicity occurs at or near=20 144 degrees.  The net effect of the Caustic is a ring of PKP=20 concentration 36 degrees away from the "antipode" of the event.  ( = Remember=20 direct P-waves observe quiet time from 103 to 144 degrees=20 )
    Although I have never = seen this=20 demo, I understand a sphere of high density glass enclosed with a sphere = of=20 lower density glass will show a similar ring of lazer light entering the = far=20 side.  Of course acoustic caustics can be=20 demonstrated.
   The few caustics noted here = (long=20 Period) have a signature very unique from the usual events of S. = Pacific. =20 The front loading of P related waves are larger than any of the other = wave=20 fronts, expecially in deep events where surface waves are=20 minimized.
   No doubt there are better=20 explanations     (Thanks Jorma)  of  this = seismic=20 phenomenon.   Do the geometry of P energy through the Core, and one = gets an=20 idea of what is going on.
          =        =20 Jim Lehman
----- Original Message -----
From:=20 Timothy=20 Carpenter
Sent: Saturday, February 05, = 2005 4:33=20 PM
Subject: RE: Iris Waveform = Chart

I should = probably=20 know – but I don't. What is the "caustic" distance? And for that = matter, what=20 is the "caustic"?

Regards,

-Tim-

 

Timothy = Carpenter, P.E., Pres.,
GeoDynamics = Consultants, Inc.
5043 Whitlow Ct.
Commerce Twp., Mi=20 48382
248-363-4529 (voice & fax)
248-766-1629 (cell)
geodynamics@...........=20 (primary)
geodynamics@.......=20 (secondary)

 

 

-----Original=20 Message-----
From:=20 psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of Connie and Jim=20 Lehman
Sent: = Sunday, January=20 09, 2005 7:03 PM
To:=20 psn-l@..............
Subject:=20 Iris Waveform Chart

 

PSN--thanks for the=20 Iris Waveform Chart for the 9.0 Sumatra  12/26/04 event.  = The=20 surface wave arrivals of multiple stations exhibited by distance, and=20 text,  makes a super graphic.  I was wondering about  = the=20 occurrence of a seismic caustic at the appropriate degree = distance.  Was=20 the gap at 160 degree area due to no reporting station near the = "caustic"=20 distance.  In periodic recording here we've copied three = caustics =20 in 20 years--I believe the events were southwest of Australia for = us--not a=20 very hot spot.

   =20 The 18 sec long period system at James Madison Un.  (Virginia) = working=20 into a graphic readout read the 8.1 Macquarie Is. event-(l2/23) = nicely, but=20 the 9.0 event read 20 min after P-diff arrived and then went off scale = for 100=20 minutes and returned to normal recording for the 7.1 event at = 04:21. =20 One can conclude, surface wave arrivals for us (at approx. = 145=20 degrees) were obscured.  Keep up the good=20 work.

           = =20 Jim = Lehman

Subject: RE: Iris Waveform Chart From: "Timothy Carpenter" GeoDynamics@....... Date: Sun, 6 Feb 2005 19:15:23 -0500 Fascinating. Thanks for the explanation. I went back and re-ran Alan = Jones's animation of wave propagation through the earth, set the cursor at about = 145 degrees and watched. That program is an excellent teaching aid. =20 So, is the term Caustic used only for the special case of the = constructive interference at 155-degrees (or 144) or is it used for any case of constructive interference? =20 -Tim- =20 Timothy Carpenter, P.E., Pres., GeoDynamics Consultants, Inc. 5043 Whitlow Ct. Commerce Twp., Mi 48382 248-363-4529 (voice & fax) 248-766-1629 (cell) geodynamics@........... (primary) geodynamics@....... (secondary) =20 =20 -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of Connie and Jim Lehman Sent: Sunday, February 06, 2005 6:18 PM To: psn-l@.............. Subject: Re: Iris Waveform Chart =20 Tim & others- =20 According to Bath, Intro. to Seismology, the author explains a seismic caustic as follows. In a model of Earth with Core 1/2 dia. of the Earth Sphere, and a ratio of density l:1.2, every point situated more than 155 degrees from the surface event will receive not one but two PKP waves = which propigate along different paths. Exactly at 155 degrees, these waves coincide and result in a great concentration of energy--or a Caustic. =20 For reasons not easily explained, this caustic --in real earth = seismicity occurs at or near 144 degrees. The net effect of the Caustic is a ring = of PKP concentration 36 degrees away from the "antipode" of the event. ( Remember direct P-waves observe quiet time from 103 to 144 degrees ) Although I have never seen this demo, I understand a sphere of high density glass enclosed with a sphere of lower density glass will show a similar ring of lazer light entering the far side. Of course acoustic caustics can be demonstrated. The few caustics noted here (long Period) have a signature very = unique from the usual events of S. Pacific. The front loading of P related = waves are larger than any of the other wave fronts, expecially in deep events where surface waves are minimized. No doubt there are better explanations (Thanks Jorma) of this seismic phenomenon. Do the geometry of P energy through the Core, and = one gets an idea of what is going on. Jim Lehman ----- Original Message -----=20 From: Timothy Carpenter =20 To: psn-l@................. Sent: Saturday, February 05, 2005 4:33 PM Subject: RE: Iris Waveform Chart =20 I should probably know =96 but I don't. What is the "caustic" distance? = And for that matter, what is the "caustic"? Regards, -Tim- =20 Timothy Carpenter, P.E., Pres., GeoDynamics Consultants, Inc. 5043 Whitlow Ct. Commerce Twp., Mi 48382 248-363-4529 (voice & fax) 248-766-1629 (cell) geodynamics@........... (primary) geodynamics@....... (secondary) =20 =20 -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of Connie and Jim Lehman Sent: Sunday, January 09, 2005 7:03 PM To: psn-l@.............. Subject: Iris Waveform Chart =20 PSN--thanks for the Iris Waveform Chart for the 9.0 Sumatra 12/26/04 = event. The surface wave arrivals of multiple stations exhibited by distance, = and text, makes a super graphic. I was wondering about the occurrence of = a seismic caustic at the appropriate degree distance. Was the gap at 160 degree area due to no reporting station near the "caustic" distance. In periodic recording here we've copied three caustics in 20 years--I = believe the events were southwest of Australia for us--not a very hot spot. The 18 sec long period system at James Madison Un. (Virginia) = working into a graphic readout read the 8.1 Macquarie Is. event-(l2/23) nicely, = but the 9.0 event read 20 min after P-diff arrived and then went off scale = for 100 minutes and returned to normal recording for the 7.1 event at 04:21. One can conclude, surface wave arrivals for us (at approx. 145 degrees) = were obscured. Keep up the good work. Jim Lehman

Fascinating. Thanks for the = explanation. I went back and re-ran Alan Jones's animation of wave propagation through = the earth, set the cursor at about 145 degrees and watched. That = program is an excellent = teaching aid.

 

So, is the term Caustic used only = for the special case of the constructive interference at 155-degrees (or 144) or = is it used for any case of constructive interference?

 

-Tim-

 

Timothy = Carpenter, P.E., Pres.,
GeoDynamics Consultants, Inc.
5043 Whitlow = Ct.
Commerce Twp., Mi 48382
248-363-4529 (voice & fax)
248-766-1629 (cell)
geodynamics@........... = (primary)
geodynamics@....... = (secondary)

 

 

-----Original = Message-----
From: = psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Connie and Jim Lehman
Sent: Sunday, February 06, 2005 6:18 PM
To: = psn-l@..............
Subject: Re: Iris = Waveform Chart

 

Tim & = others-

 

According to = Bath, Intro. to = Seismology, the author explains a seismic caustic as follows.  In a model of Earth = with Core 1/2 dia. of the Earth Sphere, and a ratio of density l:1.2, every = point situated more than 155 degrees from the surface event will receive not = one but two PKP waves which propigate along different paths.  Exactly = at 155 degrees, these waves coincide and result in a great concentration of = energy--or a Caustic. 

   For reasons = not easily explained, this caustic --in real earth seismicity occurs at or near 144 degrees.  The net effect of the Caustic is a ring of PKP concentration 36 degrees away from the "antipode" of the = event.  ( Remember direct P-waves observe quiet time from 103 to 144 degrees = )

    Although = I have never seen this demo, I understand a sphere of high density glass = enclosed with a sphere of lower density glass will show a similar ring of lazer light entering the far side.  Of course acoustic caustics can be = demonstrated.

   The few = caustics noted here (long Period) have a signature very unique from the usual events of = S. Pacific.  The front loading of P related waves are larger than any = of the other wave fronts, expecially in deep events where surface waves are = minimized.

   No doubt there = are better explanations     (Thanks Jorma)  = of  this seismic phenomenon.   Do the geometry of P energy through the Core, = and one gets an idea of what is going on.

    &nbs= p;            = ; Jim Lehman

----- Original Message = -----

To:<= /font> psn-l@..............

Sent: Saturday, February 05, 2005 4:33 PM

Subject: RE: Iris Waveform Chart

 

I should = probably know – but I don't. What is the "caustic" distance? And for = that matter, what is the "caustic"?

Regards,

-Tim-

 

Timothy Carpenter, P.E., Pres.,
GeoDynamics Consultants, Inc.
5043 Whitlow = Ct.
Commerce Twp., Mi 48382
248-363-4529 (voice & fax)
248-766-1629 (cell)
geodynamics@........... = (primary)
geodynamics@....... = (secondary)

 

 

-----Original = Message-----
From: = psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Connie and Jim Lehman
Sent: Sunday, January 09, 2005 7:03 = PM
To: = psn-l@..............
Subject: Iris Waveform = Chart

 

PSN--thanks for the Iris Waveform Chart for the 9.0 = Sumatra=   = 12/26/04 event.  The surface = wave arrivals of multiple stations exhibited by distance, and text,  = makes a super graphic.  I was wondering about  the occurrence of a = seismic caustic at the appropriate degree distance.  Was the gap at 160 = degree area due to no reporting station near the "caustic" = distance.  In periodic recording here we've copied three caustics  in 20 = years--I believe the events were southwest of = Australia<= b> for us--not a very hot = spot.

    The 18 sec long period system at James Madison Un.  (Virginia) = working into a graphic readout read the 8.1 Macquarie Is. event-(l2/23) nicely, = but the 9.0 event read 20 min after P-diff arrived and then went off scale for = 100 minutes and returned to normal recording for the 7.1 event at = 04:21.  One can conclude, surface wave arrivals for us (at approx. 145 degrees) were obscured.  Keep up the good = work.

    &nbs= p;       Jim Lehman

Subject: RE: Iris Waveform Chart From: John or Jan Lahr johnjan@........ Date: Sun, 06 Feb 2005 17:13:23 -0800 Tim,

My understanding is that a caustic is formed when the derivative of Distance with
Take-off angle is zero.  ("Distance" is the angular distance from the earthquake
to the place where the ray reaches the surface of the Earth and Take-off angle
measures the direction with respect to vertical that the ray leaves the earthquake
source.)

Other cases of constructive interference are not termed caustics as far as I
know.  I'm traveling now, so can't refer to any seismology books and have
yet to find a good explanation on a web site. 

Maybe John Taber or Alan Jones can double check me on this!

Cheers,
John

At 04:15 PM 2/6/2005, you wrote:
So, is the term Caustic used only for the special case of the constructive interference at 155-degrees (or 144) or is it used for any case of constructive interference?


X-Originating-IP: [64.21.22.120]
From: "Connie and Jim Lehman" <lehmancj@...........>
To: <psn-l@..............>
Subject: Re: Iris Waveform Chart
Date: Sun, 6 Feb 2005 18:17:50 -0500
X-Mailer: Microsoft Outlook Express 5.50.4133.2400
Reply-To: psn-l@..............
Sender: psn-l-request@..............

Tim & others-
 
According to Bath, Intro. to Seismology, the author explains a seismic caustic as follows.  In a model of Earth with Core 1/2 dia. of the Earth Sphere, and a ratio of density l:1.2, every point situated more than 155 degrees from the surface event will receive not one but two PKP waves which propigate along different paths.  Exactly at 155 degrees, these waves coincide and result in a great concentration of energy--or a Caustic. 
   For reasons not easily explained, this caustic --in real earth seismicity occurs at or near 144 degrees.  The net effect of the Caustic is a ring of PKP concentration 36 degrees away from the "antipode" of the event.  ( Remember direct P-waves observe quiet time from 103 to 144 degrees )
    Although I have never seen this demo, I understand a sphere of high density glass enclosed with a sphere of lower density glass will show a similar ring of lazer light entering the far side.  Of course acoustic caustics can be demonstrated.
   The few caustics noted here (long Period) have a signature very unique from the usual events of S. Pacific.  The front loading of P related waves are larger than any of the other wave fronts, expecially in deep events where surface waves are minimized.
   No doubt there are better explanations     (Thanks Jorma)  of  this seismic phenomenon.   Do the geometry of P energy through the Core, and one gets an idea of what is going on.
            &nbs= p;     Jim Lehman
----- Original Message -----
From: Timothy Carpenter
To: psn-l@..............=
Sent: Saturday, February 05, 2005 4:33 PM
Subject: RE: Iris Waveform Chart

I should probably know = =96 but I don't. What is the "caustic" distance? And for that= matter, what is the "caustic"?

Regards,
-Tim-
 

Timothy= Carpenter, P.E., Pres.,
GeoDynamics Consultants, Inc.
5043 Whitlow Ct.
Commerce Twp., Mi 48382
248-363-4529 (voice & fax)
248-766-1629 (cell)
geodynamics@...........= (primary)
geodynamics@.......= (secondary)

 

 

-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@..............] On Behalf Of= Connie and Jim Lehman
Sent: Sunday, January 09, 2005 7:03 PM
To: psn-l@..............
Subject: Iris Waveform Chart
 

PSN--thanks for the Iris Waveform Chart for the 9.0= Sumatra  12/26/04 event.  The surface wave arrivals of multiple= stations exhibited by distance, and text,  makes a super= graphic.  I was wondering about  the occurrence of a seismic= caustic at the appropriate degree distance.  Was the gap at 160 degree= area due to no reporting station near the "caustic"= distance.  In periodic recording here we've copied three= caustics  in 20 years--I believe the events were southwest of= Australia for us--not a very hot spot.

    The 18 sec long period system at James Madison= Un.  (Virginia) working into a graphic readout read the 8.1 Macquarie= Is. event-(l2/23) nicely, but the 9.0 event read 20 min after P-diff= arrived and then went off scale for 100 minutes and returned to normal= recording for the 7.1 event at 04:21.  One can conclude, surface wave= arrivals for us (at approx. 145 degrees) were obscured.  Keep up the= good work.

            Jim= Lehman
Subject: SAC binary file headers From: "rem11560@............ rem11560@netzero.com Date: Mon, 7 Feb 2005 02:29:58 GMT Hi all, I occasionally download SAC binary event files from the IRIS web site, primarily to compare my waveforms with that recorded by the nearby PAL and FOR stations of the LDEO network. I then use WinQuake to convert them to PSN format. In an effort to understand and use the information contained in the SAC header, I wrote a utility that reads out the 133 elements of the header. Not many of these elements contain any information on a typical file, but there is still a lot of information that is not transferred by WinQuake to the converted PSN file, including event time and location and sensor calibration. Event time is not specifically given, but is given as an offset in seconds from the starting time of the file. There is a number in the SAC header labeled "SCALE", usually a very large number, which must have to do with the gain of the sensor. Can anyone explain to me how to use this number to calculate a number to enter in WinQuake for sensor sensitivity? I have come up with an empirical formula Sensitivity = 40 * (1.0 / SCALE) which seems to come close to what gives me the response I expect from PAL and FOR, based on my own outputs, but a formula like that really doesn't make much sense to me. I hope someone out there can explain the meaning of SCALE. Cheers, Bob ______________________________________________________________________ Speed up your surfing with NetZero HiSpeed. Now includes pop-up blocker! Only $14.95/month -visit http://www.netzero.com/surf to sign up today! __________________________________________________________ Public Seismic Network Mailing List (PSN-L) Subject: RE: Iris Waveform Chart From: "Timothy Carpenter" GeoDynamics@....... Date: Mon, 7 Feb 2005 00:26:39 -0500 John, Thanks for the response. Usually I've had excellent success finding information on the web using one or the other of the several search = engines. But this time, the only things that showed up were excerpts from professional papers where the authors presumed the reader had known what = a caustic was since kindergarten. :-) (Well, actually I had, but that was caustic soda.) -Tim- -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... = On Behalf Of John or Jan Lahr Sent: Sunday, February 06, 2005 8:13 PM To: psn-l@.............. Cc: taber@......... Alan Jones Subject: RE: Iris Waveform Chart =20 Tim, My understanding is that a caustic is formed when the derivative of = Distance with=20 Take-off angle is zero. ("Distance" is the angular distance from the earthquake=20 to the place where the ray reaches the surface of the Earth and Take-off angle=20 measures the direction with respect to vertical that the ray leaves the earthquake=20 source.) Other cases of constructive interference are not termed caustics as far = as I know. I'm traveling now, so can't refer to any seismology books and = have=20 yet to find a good explanation on a web site. =20 Maybe John Taber or Alan Jones can double check me on this! Cheers, John At 04:15 PM 2/6/2005, you wrote: So, is the term Caustic used only for the special case of the = constructive interference at 155-degrees (or 144) or is it used for any case of constructive interference? X-Originating-IP: [64.21.22.120]=20 From: "Connie and Jim Lehman" =20 To: =20 Subject: Re: Iris Waveform Chart=20 Date: Sun, 6 Feb 2005 18:17:50 -0500=20 X-Mailer: Microsoft Outlook Express 5.50.4133.2400=20 Reply-To: psn-l@................. Sender: psn-l-request@................. Tim & others- =20 According to Bath, Intro. to Seismology, the author explains a seismic caustic as follows. In a model of Earth with Core 1/2 dia. of the Earth Sphere, and a ratio of density l:1.2, every point situated more than 155 degrees from the surface event will receive not one but two PKP waves = which propigate along different paths. Exactly at 155 degrees, these waves coincide and result in a great concentration of energy--or a Caustic. =20 For reasons not easily explained, this caustic --in real earth = seismicity occurs at or near 144 degrees. The net effect of the Caustic is a ring = of PKP concentration 36 degrees away from the "antipode" of the event. ( Remember direct P-waves observe quiet time from 103 to 144 degrees ) Although I have never seen this demo, I understand a sphere