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.
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?
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