Finite Fault Model

Preliminary Result of the Jan 12, 2010 Mw 7.0 Haiti Earthquake

Gavin Hayes, NEIC


DATA Process and Inversion

We used the GSN broadband waveforms downloaded from the NEIC data center. We analyzed 12 teleseismic broadband P waveforms, 8 broadband SH waveforms, and 25 long period surface waves 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 (Lat.=18.46 deg.; Lon.=-72.53 deg.). The fault planes are defined using the centroid moment tensor solution of the gCMT group, adjusted to match the surface geometry of the mapped fault.


Result

After comparing the waveform fits based on two planes, we find that the nodal plane (strike=262.0 deg., dip=70.0 deg.) fits the data better. The seismic moment release based upon this plane is 4.95E+026 dyne.cm using a 1D crustal model interpolated from CRUST2.0 (Bassin et al., 2000).

Cross-section of slip distribution



Figure 1. Cross-section of slip distribution. The strike direction of fault plane is indicated by the black arrow and the hypocenter location is denoted by the red star. The slip amplitude are showed in color and motion direction of the hanging wall relative to the footwall is indicated by white arrows. Contours show the rupture initiation time in seconds.


Moment Rate Function



Figure 2. Source time function, describing the rate of moment release with time after earthquake origin.


Comparison of data and synthetic seismograms



Figure 3. Comparison of teleseismic body waves. The data is 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 is the epicentral distance. Shading describes relative weighting of the waveforms.




Figure 4.1. Comparison of long period surface waves. The data is 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 is the epicentral distance. Shading describes relative weighting of the waveforms.




Figure 4.2. Comparison of long period surface waves. The data is 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 is the epicentral distance. Shading describes relative weighting of the waveforms.




Figure 5. Surface projection of the slip distribution superimposed on ETOPO2. The dark gray circles indicate the locations of ~20 hours of aftershocks.


Gavin's Comments:

The fault planes of available moment tensors (gCMT, USGS W-Phase and USGS MT) indicate fault strike oriented at ~252. While data misfits are reduced using this plane, we have adjusted the orientation to match the trend of the fault at the surface. All inversions indicate slip to the east and west of the epicenter (i.e. somewhat bilateral), though peak slip is concentrated at the hypoocenter and west.


Slip Distribution


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.


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. G. Hayes at the NEIC.