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Preliminary Result
05/06/13 (Mw 7.8) Tarapaca, Chile Earthquake

Chen Ji, Caltech

DATA Process and Inversion

We used the GSN broadband data downloaded from the NEIC data center. We analyzed 7 teleseismic P waveforms and 5 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.=-19.903 deg.; Lat.=-69.128 deg. Hypocenter depth = 101 km). The fault planes are defined using the quick moment tensor solution of HARVARD.

Result

After comparing the waveform fits based on two planes, we find that the high angle nodal plane (strike=325 deg., dip=75 deg.) fits the data better. The seismic moment release based upon this plane is 6.17x10**27 dyne.cm.

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. The ocean is plotted in blue and land is plotted in green. The black line indicates the plate boundary.

CJ's Comments:

The model is very preliminary. It may change when more data become available.

Download

(Slip Distribution, Not available yet)
SUBFAULT FORMAT CMTSOLUTION FORMAT

References

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).
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