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Earthquake Hazards Program

Monday, July 17, 2006 at 08:19:28 UTC

Preliminary Result of the 2006 July 17 Magnitude 7.7 - SOUTH OF JAVA, INDONESIA Earthquake

Chen Ji, UCSB

DATA Process and Inversion

We used the GSN broadband data downloaded from the NEIC data center. We analyzed 16 teleseismic P waveforms and 14 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.=-9.2900 deg.; Lat.=107.3500 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=288.94 deg., dip=10.35 deg.) fits the data better. The seismic moment release based upon this plane is 3.7e+27 using a 1D crustal model interpolated from CRUST2.0 (Bassin et al., 2000).

Cross-section of slip distribution

Figure 1: 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 2: 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 3: 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 shows the plate boundary (Bird, 2002).

CJ's Comments:

1) The fault dip is not well resolved yet. The location of slip depends on the location of hypocenter.

2) The average rupture velocity is about 1.1 km/sec and the average rise time is about 8 sec.

3) The slip around -200 km in Figure 1 may not be well resolved.

4) Total rupture duration may be over 200 sec but most of moment released in the first 140 sec.




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.

Acknowledgement and Contact Information

This work is supported by National Earthquake Information Center (NEIC) of United States Geological Survey. This web page is built and maintained by Dr. C. Ji at UCSB.


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