Finite Fault Model
Updated Result of the Feb 27, 2010 Mw 8.8 Maule, Chile Earthquake
Gavin Hayes, NEIC
DATA Process and Inversion
This is an updated solution, adjusted to include more data, and improved body wave onset times. The original solution is linked from the base of this page. We used GSN broadband waveforms downloaded from the NEIC waveform server. We analyzed 25 teleseismic broadband P waveforms, 13 broadband SH waveforms, and 39 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.=-35.85 deg.; Lat.=-72.72 deg.; Dep.=35 km). The fault plane is defined using the W-phase moment tensor solution of the NEIC, adjusted to match the local dip of the subducting slab.
Result
After comparing the waveform fits based on two planes, we find that the nodal plane (strike=17.5 deg., dip=18.0 deg.) fits the data better. The seismic moment release based upon this plane is 2.39E+029 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 3.1. 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 3.2. 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 GEBCO. Red lines indicate major plate boundaries [Bird, 2003]. Gray circles are aftershock locations, sized by magnitude, up to 2010/03/02 15:30 UTC.
Gavin's Comments:
The original solution can be found here.
Slip Distribution
Alternate Solutions
Chen Ji, UCSB
Anthony Sladen, Caltech
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,
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.
