Surface Deformation and Slip Distribution of the 1994 Northridge Earthquake Determined from InSAR
Abstract
The January 17, 1994 M6.7 Northridge earthquake occurred in the densely populated suburbs to the northwest of Los Angeles, California. Occurring on a previously unknown blind thrust fault, it was the most costly earthquake in United States history causing 60 deaths and ~20 billion dollars in damage. In the interval since the earthquake, several other blind thrusts have been identified in the area. In order to quantify the influence, in terms of stress changes, of the Northridge event on surrounding faults detailed knowledge of the location, orientation and amount of fault slip is important. Existing Interferometric Synthetic Aperture Radar (InSAR) models of this earthquake typically were developed by fitting the pattern of displacements by trial and error, and were therefore somewhat subjective. In the 15 years since the original studies were published a number of new modeling tools and community data products have been developed that should enable us to produce more detailed, objective and robust results. We measure the coseismic deformation of this earthquake using InSAR. A pair of descending images from the European Space Agency's ERS-1 satellite, spanning from 11/08/1993 to 12/06/1995, containing the earthquake are processed using the ROI_PAC software, and show uplift of up to ~45 cm centered on 118.508° W, 34.321° N. These data have been subsampled using a quadtree decomposition. Using this data, we first employ a nonlinear inversion to determine the parameters of the single rectangular dislocation that best fits the data. The best-fitting fault has strike: 110°, dip: 40.6° to the southwest, length: 14.2 km, width: 8.5 km, top fault depth: 6.7 km, slip: 2m, and moment: 1.1*1019 Nm. These results are relatively consistent with other published geodetic work (eg. Hudnut, 1996, Massonnet and Feigl, 1996), and the global CMT moment estimate. In detail, however, slip on a single rectangular dislocation does not completely model the observed deformation. Residual deformation to the west of our best-fitting single dislocation suggests that additional fault segments may have ruptured in the Northridge earthquake (eg. Massonnet and Feigl, 1996). In order to investigate this, we solve for a detailed slip distribution for the event in a non-negative least squares sense, using a non-planar triangular element fault mesh modified from the SCEC Community Fault Model (CFM) and the Poly3D code to calculate model displacements. This model shows a main asperity, with peak slip of ~3 m over a depth range of 10-16 km, bounded at its western edge by a geometrical barrier, a down-dip parallel corrugation in the fault. Secondary slip of about 0.6 m to the west of this feature is also present, and is the likely source of the residual deformation in our original single dislocation model.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMNH53A1726S
- Keywords:
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- 0545 COMPUTATIONAL GEOPHYSICS / Modeling;
- 1240 GEODESY AND GRAVITY / Satellite geodesy: results;
- 8110 TECTONOPHYSICS / Continental tectonics: general;
- 4337 NATURAL HAZARDS / Remote sensing and disasters