Preliminary Finite Fault Results for the Nov 13, 2016 Mw 7.9 -42.7570,173.0770 Earthquake (Version 1)


DATA Process and Inversion

We used GSN broadband waveforms downloaded from the NEIC waveform server. We analyzed 60 teleseismic broadband P waveforms, 29 broadband SH waveforms, and 47 long period surface waves selected based on data quality and azimuthal distribution. Waveforms are first converted to displacement by removing the instrument response and are then used to constrain the slip history using a finite fault inverse algorithm (Ji et al., 2002). We begin modeling using a hypocenter matching or adjusted slightly from the initial NEIC solution (Lon. = 173.1 deg.; Lat. = -42.8 deg., Dep. = 16.0 km), and a fault plane defined using either the rapid W-Phase moment tensor (for near-real time solutions), or the gCMT moment tensor (for historic solutions).


Result

After comparing waveform fits based on the two planes of the input moment tensor, we find that a solution adjusted from the nodal plane striking towards 255.0 deg. fits the data better. The adjusted solution uses 5 plane segments (see Table 1 below) designed to match a priori knowledge of the fault (e.g., 3D slab geometry). The seismic moment release based upon this solution is 9.0e+27 dyne.cm (Mw = 7.9) using a 1D crustal model interpolated from CRUST2.0 (Bassin et al., 2000).
SegmentStrike (deg.)Dip (deg.)
1255.080.0
2225.036.0
3225.036.0
4225.070.0
5245.070.0

Table 1. Multi-Segment Parameters.



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 (up to 7 days), sized by magnitude.


Cross-section of slip distribution



Cross-section of slip distribution. The strike direction is indicated above each fault plane and the hypocenter location is denoted by a star. Slip amplitude is shown in color and the motion direction of the hanging wall relative to the footwall (rake angle) is indicated with arrows. Contours show the rupture initiation time in seconds.


Moment Rate Function




Source time function, describing the rate of moment release with time after earthquake origin, relative to the peak moment rate (listed in the top right corner of the plot).


Comparison of data and synthetic seismograms




Comparison of teleseismic body waves. Data are shown in black and 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; below is the epicentral distance. Shading describes relative weighting of the waveforms.




Comparison of teleseismic body waves. Data are shown in black and 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; below is the epicentral distance. Shading describes relative weighting of the waveforms.




Comparison of teleseismic body waves. Data are shown in black and 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; below is the epicentral distance. Shading describes relative weighting of the waveforms.




Comparison of teleseismic body waves. Data are shown in black and 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; below is the epicentral distance. Shading describes relative weighting of the waveforms.




Comparison of long period surface waves. Data are shown in black and 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.




Comparison of long period surface waves. Data are shown in black and 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.




Comparison of long period surface waves. Data are shown in black and 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.


Scientific Analysis:

Delayed onset of main energy release, and presence of multiple surface ruptures, makes modeling complicated. Moment tensor solutions imply deeper, predominantly thrust motion necessary to model rupture. Rotation of rake angles in solution indicates rupture on multiple faults as well; both deeper thrust and shallow strike-slip.

Slip Distribution:

The plots above and a variety of data files for the finite fault solution in different formats can be obtained by clicking on the Downloads tab below.

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.

Ji, C., D. V. Helmberger, D. J. Wald, and K. F. Ma (2003), Slip history and dynamic implications of the 1999 Chi-Chi, Taiwan, earthquake, J Geophys Res-Sol Ea, 108(B9).

Shao, G. F., X. Y. Li, C. Ji, and T. Maeda (2011), Focal mechanism and slip history of the 2011 M-w 9.1 off the Pacific coast of Tohoku Earthquake, constrained with teleseismic body and surface waves, Earth Planets Space, 63(7), 559-564.


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.