PSN-L Email List Message

Subject: Re: Chilean quake
From: Bob Hancock icarus@.........
Date: Sun, 28 Feb 2010 12:35:52 -0700

They was only have one focal mechanism published at this time for the =
100228 M 6.1 event, while there are three focal mechanism solutions =
published for the 100227 M 8.8 event.  Each of these focal mechanisms =
were determined by different algorithms, and while there similarities, =
you cannot make a direct comparison between the two events at this time, =
until you have two focal mechanism determined by the same algorithm.  =
The Global CMT (Centroid Moment Tensor) catalog is maintained by Harvard =
University and while it has published the focal mechanism for the M 8.8 =
event, it has not published the focal mechanism for the M 6.1 event.  =
This information should be available in a few days and that would allow =
for a direct comparison at that time.

However, that being said, all four focal mechanisms appear to be =
similar.  The maximum spread on strike was 21 degrees, The maximum =
spread on dip was 14 degrees.  The maximum spread on slip was 24 =

Peak P and Rayleigh wave amplitudes are associated the middle of the =
nodal planes, and peak S and Love Wave amplitudes are associated with =
the nodal plane lines.

Although the available data indicates that the strike, dip, and slip are =
close, if your station location falls into different nodal planes from =
the two events, you could see significantly different wave amplitudes =
and direction of initial of wave movement.

Another way is to download data from either the IU, US, or Transportable =
Array along the closest ray path to your station and compare the =
results.  This may or may not be possible depending upon your station =

Bob Hancock
Three Points, AZ

On Feb 28, 2010, at 10:37 AM, Thomas Dick wrote:

> Referring to the 8.8 quake 2/27/10 and the 6.1 quake at 11:25:34 =
2/28/10....according to the "rules", "P" larger on broadside and "S" is =
larger on the end .....the quakes were at long. 72 and I am at 87 ..... =
"S" didn't seem to follow that rule ... or did I miss something? is this =
a depth issue??
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