Thread: Nevada earthquake, recent Indonesian Eqs

Started: 2008-02-28 17:16:08
Last activity: 2008-02-28 17:16:08
Topics: IRIS EPO
Larry Braile
2008-02-28 17:16:08
Some recent earthquake and AS-1 seismogram information:

1. The Feb. 21, 2008 NE Nevada earthquake produced a seismogram with
excellent S arrivals at many stations (see attached seismogram for the
WLIN station or examine records available for download from SpiNet).
Because of the very visible S arrivals and the location of the event
(away from the west coast), this event provides an excellent opportunity
for developing an S minus P Eq location activity using only AS-1
records. I have a couple of suitable seismograms, but would like to see
seismograms from WA, OR, CA, NM, TX. If you have a well-recorded
seismogram from this event, please email it as a sac file (attachment)
or upload to SpiNet. Please include your station name (4-letter code)
in the file name. Thanks! By the way, I have recently updated some
online information on identifying the S arrival on AS-1 seismograms and
using the S and P arrivals to estimate epicenter-to-station distance
("Identifying the S arrival on AS-1 Seismograms and estimating distance
using the S minus P method",
http://web.ics.purdue.edu/~braile/edumod/as1lessons/Swave/Swave.htm).

2. You probably noticed the recent Indonesian earthquakes (Kepulauan
Mentawai region) of February 23-25 (see screen image from February 27,
attached, of the USGS M5+ earthquake list - .
http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/quakes_big.php).
There were several events that produced good seismograms on AS-1 records
in the U.S. (about 120 degrees or more from the epicenter).
Interestingly, the M5.4 and 6.4 earthquakes on February 23 and 24 appear
to be foreshocks of the M7.0 earthquake of February 25. The M7.0 event
was followed by aftershocks including the M6.4 and M6.6 earthquakes
later in the day on the 25th. I happened to check my online screen
image (http://www.iris.edu/amaseis/schools/fullview.phtml?code=WLIN) for
the WLIN station, and the USGS M5+ earthquake list about fifteen minutes
after 4 pm EST (21:00 GMT) on February 25. The seismic record was
quiet, but the USGS had already posted the M6.6 event (21:02:18 Feb. 25,
2008) on the earthquake list (based on recordings close to the epicenter
and available in near real time through the internet or other data
transmissions). Recognizing that this event was in the same area as the
earlier M7.0 quake, I knew that the travel time from the epicenter to
the WLIN station was about 20 minutes, so I knew that in a few minutes,
the signal from the M6.6 event would arrive at the WLIN station (as it
did). Not really earthquake prediction, but it was a very interesting
occurrence that I have experienced only a few times in many years of
monitoring earthquakes with the AS-1 seismograph.

-Larry Braile

--
Lawrence W. Braile, Professor and Department Head
Department of Earth and Atmospheric Sciences
550 Stadium Mall Drive
Purdue University
West Lafayette, IN 47907-2051
(765) 494-5979 (O), (765) 496-1210 (Fax)
E-mail: braile<at>purdue.edu <braile<at>purdue.edu>
Web page: http://web.ics.purdue.edu/~braile
http://web.ics.purdue.edu/%7Ebraile
Departmental web page: http://www.purdue.edu/eas/
http://www.purdue.edu/eas/
SAGE web page: http://www.sage.lanl.gov/

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