Name: _____________________________________________________
Homework 5: SAC
Due Nov. 10th
Teleseismic Waveforms
1. Download data for a significant recent earthquake using the IRIS Wilber II website:
http://www.iris.edu/dms/wilber.htm. I have assigned events below:
Akram:
Lauren:
Rebecca:
Jordan:
Brian:
Yanjun:
Onur:
Merhdad:
2010 11 25: Southern Sumatra, Indonesia, Magnitude 7.7
2010 10 03: South Islands, New Zealand, Magnitude 7.0
2010 02 27: Maule, Chile, Magnitude 8.8
2010 01 12: Haiti, Magnitude 7.0
2009 10 29: Samoa Islands, Magnitude 8.1
2008 05 12: Eastern Sichuan, China, Magnitude 7.9
2007 01 13: Kuril Islands, Magnitude 8.1
2007 04 01: Solomon Islands, Magnitude 8.1
Download only broadband Global Seismic Network Stations at BH* channels with good signal to
noise ratios, distances between 30º and 90º, and distributed every 2º. Request data 2 minutes prior
to the P wave and 20 minutes after the P wave. Download data as a SEED volume.
2. Use the command ‘rdseed’ to extract only ‘Q’ or quality rated data. Be sure to extract the response
information (RESP format, not poles/zeros) in addition to the waveforms.
Where is this data located: _________________________________________________
3. Pick a good station, here defined as a station recording high amplitude P and S arrivals on the
velocity seismograms.
a. Use a bandpass filter to filter the waveforms (BHZ, BHE, and BHN) to reduce noise
and highlight the recorded phases. Write out the full command below.
b. Cut the data to 1 minute prior to the approximate P until the end of the event
waveform or the end of file if the full waveform was not downloaded from IRIS.
c. Save the cut data under new file names.
d. Plot the cut data and label the x and y-axes of this plot. Provide information about
the filter as a plot title. Save the plot to a postscript file.
Filter: _________________________________________________________________________
Cut data names: ______________________________________________________________
Plot name and directory: ____________________________________________________
4. Using the three raw waveforms (BHZ, BHE, and BHN), remove the instrument response (use
evalresp command), filter and cut the resulting displacement data as in number 3, and save the
displacement waveforms to three new files.
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Displacement data names: _________________________________________________
5. Using the cut velocity waveforms from number 3, read in and rotate the horizontal components to
radial and transverse components. Save these rotated data under new nams. Plot the vertical, radial
and transverse data and save this plot to a postscript file. Label the plot as appropriate.
Radial and Transverse file names: __________________________________________
Plot name and directory: ____________________________________________________
2 Bonus pts: Add the predicted teleseismic phase arrival times to the rotated waveforms prior to
plotting in number 5. Hint: use the SAC command ‘traveltime’.
Local Earthquakes
6. Copy waveforms for a New Madrid Seismic Zone earthquake listed below to a new working
directory:
2008/05/12 08:19:53 36.500N 89.530W 6.7 10 km ( 6 mi) S of New Madrid, MO
This data can be copied from /gaia/data/seisnet/NM/2008/Loc/20080512_131940_MAN. Make
sure you only copy the EHZ, EHE, and EHN channels.
Where is this data located: _________________________________________________
7. This data is referenced to the origin time of the event. Read in the vertical channels and plot the
waveforms on a single page. Based on what you see, what station is likely located closest to the
earthquake? What station is furthest away?
Closest: ______________________________________________________________________
Furthest: _____________________________________________________________________
8. Write a sac macro to insert the event and station information in the sac headers of all of the files.
Run this macro.
Location of file: _________________________________________________
9. Read in the all three components of station GLST. Using ppk, pick the P and S arrival time using the
‘p’ and ‘s’ option in ppk. Remember, P waves should be picked on the vertical component and S
waves on the horizontals (choose the best horizontal in this case). Don‘t forget to save this
information to the header using wh before quitting SAC! Write this out to a hypo file.
1Bonus pts: Pick, identify, and save the third arrival present on this station to the t1 header value.
What is this phase? ________________________________________________________
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