04/11/15 09:06:55.72 (Mw=7.1) Near
West Coast of Colombia Earthquake
Chen Ji, Caltech
DATA Process and Inversion
We used the GSN broadband data downloaded from the IRIS DMC. We analyzed 14 teleseismic
P waveforms and 11 SH waveforms selected based upon data quality and azimuthal
distribution. Waveforms are first converted to displacement by removing the instrument
response and then used to constrain the slip history based on a finite fault
inverse algorithm (Ji et al, 2002). We use the hypocenter of the USGS (Lon.=-77.539
deg.; Lat.=4.610 deg.). The fault planes are defined using the quick moment tensor
solution of the HARVARD.
After comparing the waveform fits based on two planes, we find that the nodal
plane (strike=22 deg., dip=16 deg.) fits the data better. The seismic moment
release based upon this plane is 0.6x10**27 dyne.cm using a 1D crustal model
interpolated from CRUST2.0 (Bassin et al., 2000).
Cross-section of slip distribution
Figure: The big black arrow shows the fault's strike. The colors show the slip
amplitude and white arrows indicate the direction of motion of the hanging wall
relative to the footwall. Contours show the rupture initiation time and the red
star indicates the hypocenter location.
Comparison of data and synthetic seismograms
Figure: The Data are shown in black and the synthetic seismograms are plotted
in red. Both data and synthetic seismograms are aligned on the P or SH arrivals.
The number at the end of each trace is the peak amplitude of the observation
in micro-meter. The number above the beginning of each trace is the source azimuth
and below it is the epicentral distance.
Figure: Surface projection of the slip distribution supperimposed on topography
and bathymetry map ETOPO2. The ocean is plotted in blue and land is plotted in
green. The black line indicates the plate boundary.
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Download (Slip Distribution, Not available yet)
Ji, C., D.J. Wald, and D.V. Helmberger, Source description of the 1999 Hector
Mine, California earthquake; Part I: Wavelet domain inversion theory and resolution
analysis, Bull. Seism. Soc. Am., Vol 92, No. 4. pp. 1192-1207, 2002.
Bassin, C., Laske, G. and Masters, G., The Current Limits of Resolution for
Surface Wave Tomography in North America, EOS Trans AGU, 81, F897, 2000.
GCMT project: http://www.globalcmt.org/
USGS National Earthquake Information Center: http://neic.usgs.gov
Global Seismographic Network (GSN) is a cooperative scientific facility operated jointly by the Incorporated Research Institutions for Seismology (IRIS), the United States Geological Survey (USGS), and the National Science Foundation (NSF).