PSN-L Email List Message

Subject: Re: Artic quake
From: Bob Hancock carpediem1@.........
Date: Tue, 18 Nov 2008 00:29:35 -0700

Hi Tom -

I downloaded your event and looked at it.

Your recording show a strong amplitude wave on the north horizontal  
channel and the vertical channel at the same time.  This is consistent  
with recording both vertical motion and transverse motion at the same  
time.  There are a few times when a love wave can be converted to a  
rayleigh wave and then takes on the visual characteristics of a  
rayleigh wave, but this does not appear to be within that category.   
For reference look at my posting of the same event.

  As for what wave you were seeing,  The large amplitude wave that is  
visible between the WinQuake projections for the SSS wave and LQ  
(Love) wave indicators is infact the Love Wave.
The projected arrival times of body waves is usually accurate within 1  
or 2 seconds.  However, the arrival time of surface waves is  
compounded by the type of crust they are traveling through and the  
frequencies of the waves.  The velocities of surface waves vary  
significantly from Continental Crust and Oceanic Crust with wave  
frequency contiributing significantly to this variation. I am unaware  
of a single standing wave arrival time program that will cover these  

Both Love and Rayleigh waves start out as low frequency waves and  
change to higher frequency as the progress.  Also there are changes in  
the amplitude of the waves as they progress.  However, the start of  
love and rayleigh waves can be difficult to ascertain.  Wave  
identification of surface waves is tricky at best, and sometimes the  
only way it can be confirmed is to rotate the data and look at the  
particle motion on both the horizontal channels and vertical channel.

The program used by professional seismologists SAC (Seismic Analysis  
Code), and another seismic wave timing program written by the  
Seismologists at the University of South Carolina called TauP track  
the arrival times of certain body waves.  Neither program tracks the  
arrival times of surface waves.

There is one USGS program that tracks the arrival times of surface  
wave and it is available at the following link:

The USGS projected arrival times for the Love (LQ) and Rayleigh (LR)  
waves at your station were LQ   13:16:53  and LR  13:19:15.

The projected arrival times for the Love and Rayleigh waves using  
WinQuake at your station were LQ 13:22:17.9 and LR 13:26:10.5

Neither WinQuake or the USGS program give good arrival times on  
surface waves consistently.

Looking visually at your posted seismogram, it appears that your love  
wave starts at about 13:18:30.5.  This is visible on both your north  
and east channels.  The Love wave is a transverse wave and will not  
appear in the radial.  While this event was mostly north of you, there  
was also a small horizontal component in it also.

The actual start of the Rayleigh wave is harder to identify without  
looking at particle motion.  It appears to possibly start about  
13:21:52.3 on the East and Vertical channels.  I could be wrong on the  
actual starting times, but that is the way they appear to me.

I hope this helps.

Bob Hancock

On Nov 17, 2008, at 7:57 AM, Thomas Dick wrote:

> Any one getting an unusual peak as I am after the SSS and before the  
> LQ on the vertical and N-S Lehman?
> __________________________________________________________
> 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 ]