PSN-L Email List Message

Subject: Re[2]: unusual frequency
From: Angel sismos@..............
Date: Fri, 7 Nov 2008 10:49:23 +0000

Hello Bob,

The diminished S wave might be a source mechanism thing.  The P and S radiated energy is lobed, not circular and uniform.  Some station might be in the azimuth between the radiation lobes of the S.  Some directions see an S and other don't.  Deep event also tend to have diminished S waves.


Sunday, November 2, 2008, 11:17:21 PM, you wrote:

> 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

>>>> -
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