Finite Fault Model
Updated Result of the Mar 11, 2011 Mw 9.0 Earthquake Offshore Honshu, Japan
Gavin Hayes, USGS
Data Process and Inversion
We used GSN broadband waveforms downloaded from the NEIC waveform server. We analyzed 39 teleseismic broadband P waveforms, 22 broadband SH waveforms, and 55 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.=142.37 deg.; Lat.=38.32 deg.). The fault planes are defined using the updated W-Phase moment tensor solution of the NEIC, adjusted to match local slab geometry.
Result
After analyzing waveform fits based on the nodal planes of the rapid WCMT moment tensor, and those more closely matching the slab geometry, we find that a nodal plane striking 195 deg., and dipping 10 deg., fits the data better. The seismic moment release based upon this plane is 4.90e+29 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
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.
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 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-meters. 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 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-meters. 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 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 is the epicentral distance. Shading describes relative
weighting of the waveforms.
Figure 4.2. Comparison of long period surface waves. 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 is the epicentral distance. Shading describes relative
weighting of the waveforms.
Figure 4.3. Comparison of long period surface waves. 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 is the epicentral distance. Shading describes relative
weighting of the waveforms.
Figure 5. Surface projection of the slip distribution superimposed on
GEBCO bathymetry. Red lines indicate major plate boundaries [Bird,
2003]. Gray circles, if present, are aftershock locations, sized by
magnitude.
Gavin's Comments:
The original solution can be found here.
Alternate Solutions:
Guangfu Shao and Chen Ji, UCSB
Yuji Yagi, University of Tsukuba
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. G. Hayes is contracted to work for the NEIC by Synergetics, Inc.
