Thread: Filtering - November 14, 2007 M7.7 N. Chile Earthquake

Started: 2008-01-02 16:23:52
Last activity: 2008-01-02 16:23:52
Topics: IRIS EPO
Just after the November 14, 2007 M7.7 N. Chile Earthquake I noticed an
unusual high-frequency arrival overlapping the long period surface waves
on the seismogram for this event that was recorded on the WLIN AS-1
station. I high-pass filtered the seismogram and assumed that the
resulting arrival was from an aftershock about 29 minutes after the main
shock. I checked with the USGS earthquake list for the next few days
and didn't find an aftershock at the appropriate time so I looked for
another explanation for the high frequency arrival. I gathered some
additional data and eventually figured out the clues to the explanation
for the mystery arrival - it's quite surprising.

All this led me to write up some information on filtering seismograms.
The discussion of examples is located at:
http://web.ics.purdue.edu/~braile/edumod/as1lessons/filtering/filtering.htm.
An MS Word version and a pdf version (easier printing) is also
available. At the end of the write-up, there are several suggested
activities for further exploration.

The filtering write-up is also linked from the list of additional AS-1
activities and resources at:
http://web.ics.purdue.edu/~braile/edumod/as1lessons/as1lessons.htm

Have fun trying out the seismogram filtering activities (all you need is
AmaSeis installed on your computer)! If you have a seismogram of this
earthquake from your station, also try filtering it to find the mystery
arrival (and some aftershocks).

Happy New Year!

-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/

01:07:02 v.b1cd4f60