Finite Fault Model

Updated Result of the Oct 23, 2011 Mw 7.1 Eastern Turkey Earthquake

Gavin Hayes, USGS NEIC


DATA Process and Inversion

We used GSN broadband waveforms downloaded from the NEIC waveform server. We analyzed 45 teleseismic broadband P waveforms, 32 broadband SH waveforms, and 73 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 USGS hypocenter (Lon.=38.62 deg.; Lat.=43.48 deg.). The fault planes are defined using the updated NEIC W-Phase moment tensor solution.


Result

After comparing the waveform fits based on the two nodal planes of the moment tensor, and using aftershock distribution information, we suggest the second plane is the most likely rupture surface (NP2 strike=241 deg., dip=51 deg.). The seismic moment release based upon this planes is 5.16e+26 dyne.cm (Mw7.11), using a 1D crustal model interpolated from CRUST2.0 (Bassin et al., 2000).

While these data indicate a preference for the north-dipping plane, the dip of that plane is less certain; here we use a dip of 51 degrees from the W-phase moment tensor, but shallower dips (down to ~45 degrees) fit the data equally well, and still shallower dips - similar to the gCMT dip of 36 degrees - cannot be ruled out.

Our preferred model is tied to a relocated hypocenter from Eric Bergman, and a depth from USGS broadband depth estimates. Based on this location, this KMZ FILE shows surface projections of planes dipping at 45-51 degrees, which correlate well with preliminary InSAR results, and information from geologists mapping surface rupture in the field.

Waveform fits can be downloaded here.

The original solution can be found here.


Figures



Figure 1. Cross-section of slip distribution. The strike direction of the 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 black arrows. Contours show the rupture initiation time in seconds.




Figure 2. Basemap of slip distribution overlain on topography data from GEBCO. Red circles show main and aftershock relocations from Eric Bergman. Grey circles are foreshocks, also from Bergman. The panel above the map shows the moment rate function of our modeled slip distribution.




Figure 3. Basemap of slip distribution overlain on topography data from GEBCO. Additional yellow circles are aftershock locations from DEPREM.




Figure 4. Cross-sections A and B through hypocenteral data plotted above. Lines are perpendicular to WCMT nodal planes (shown dashed in cross-sections).


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 the National Earthquake Information Center (NEIC) of United States Geological Survey. This web page is built and maintained by Dr. G. Hayes at the NEIC.