PSN-L Email List Message

Subject: Re: unusual frequency
From: Bob Hancock carpediem1@.........
Date: Sun, 2 Nov 2008 16:17:21 -0700

Without knowing the epicenter of the event, you cannot draw too many  
conclusions.  I downloaded the event using VASE, and look at it with  
SAC.  I used the unfiltered raw data from the IU/TUC station (STS-1)  
and believe the P wave arrival time is 13:36:20 for that station.  I  
can pick out the Love & Rayleigh waves.  However, the S wave is of  
very low amplitude.  I observed one very low amplitude oscillation  
that could correspond to an S wave about 13:37:25, for a S-P time of  
65 seconds or 4.47 degrees ( 496.75 km).  In addition, the rayleigh  
waves are much more pronounced on the vertical and north channels  
which would be consistent with an event that is more southerly from  
the receiving station than southwest.  The Love waves first appear  
about 13:37:45, and the Rayleigh waves appear about 13:38:25.  Without  
more information, it is not really possible to draw any conclusions on  
why there was a diminished S wave.  I have not looked at the event  
with other than my station and Tucson.  To me, it looks like a normal  
regional event, but with a magnitude of less than 4.0, most likely  
south of the border in Mexico.

Keep in mind one big problem in analyzing regional events is there is  
insufficient time for good wave separation.  They are all together and  
that can complicate trying to pick out individual waves.

Bob Hancock

On Nov 2, 2008, at 2:11 AM, Geoff wrote:

> Hello Bob;
> me Not being a physics major or math person.
> Thats Interesting since I had a s-p or s-L time
> of 2 minutes and that translates to
> 600 + miles maybe 700. This event set off
> my automatic recording which usually does
> not happen unless the quake is about 4.0
> at 400 miles. For some reason more energy then
> expected has arrived at this station sort of like
> what bubbleheads ( submarine sailors )
> might call a convergence zone
> which happens in the ocean with sound waves.
> Maybe quake waves in the earth behave like
> sound waves in the ocean and are lazy which
> will focus the energy at discreet distances
> from the event. By lazy I mean they seem
> to bend ( refract ) to the slowest velocity hitting the surface
> with concentrated focused energy
> in concentric rings around the event out to
> some distance. Such behavior requires enough
> depth of the strata to allow for this bending to happen.
> Does this mean possibly deep crust or from the mantel ?
> I should imagine the moho would keep a CZ zone
> from the crust because it would reflect at that point
> and divide the energy instead of refracting it.
> What do you think might be going on that
> would concentrate the energy from a less than
> usual quake to set off my recording alarm ?
> I understand wave velocity changes is the best way
> to guess how waves are effected as they propagate.
> Any sudden change is like a mirror and a gradual
> change is like a lens.
> I understand a transmitted ( radio wave ) signal can be bent
> by having a series of antennas with a phasing
> slightly later from antenna to antenna so that
> the delaying of the phases of a single wave
> will make the antenna behave as a massive
> variable lens thus the phased array kind of antenna
> or wullenwebber array.
> Since we can not do what mother nature has
> not already done in one way or another I can
> imagine the earth itself is somehow making
> areas of more and less energy as energy spreads
> away from the focal point. I must have been
> in an increased energy point if the quake
> was less than 4.0 and 600 miles away.
> Regards;
> geoff
> ----- Original Message ----- From: "Bob Hancock"  
> To: 
> Sent: Saturday, November 01, 2008 8:16 PM
> Subject: Re: unusual frequency
>> This event appears to be consistent with other low magnitude  
>> events  that  have occurred to the Southwest of Tucson, AZ.  I have  
>> seen other  events that are similar, and no information was ever  
>> posted on them.   I noticed the event was visible across the lower  
>> 48 states, and  southern Alaska.  It is most likely less than M 4.0  
>> as that is the  USGS minimum cutoff for display of information on  
>> international events.
>> Bob Hancock
>> On Nov 1, 2008, at 2:53 PM, Geoff wrote:
>>> Hello Mr. Thomas Dick;
>>> My Sensor located very close to 33.42138N  -111.57477W about   
>>> 507Meters above mean sea level.
>>> I saw that TUC near Tucson also saw this signal about 1336 to  
>>> 1338  on 31OCT2008 UTC.
>>> I have not analyzed it to get an accurate and precise time simply   
>>> because I can not
>>> tell for sure it is in fact an Earthquake. If no one else is   
>>> reporting it I do not trust
>>> what I am looking at. In order for me to properly read a signal  
>>> it  takes extra effort
>>> which translates to opportunity costs ( such as Battlefield 2142   
>>> time ) so I will not
>>> pursue more knowledge in detail if I can not verify the source   
>>> beforehand.
>>> The distance seems 600 miles to 700 miles from here maybe  
>>> magnitude 4
>>> but nothing seems to match that as of my last look.
>>> Regards;
>>> geoff
>>> -
>> __________________________________________________________
>> 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 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 for more information.


Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]