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Slip History of the 16 October 1999 M_w 7.1 Hector Mine Earthquake (California) from the Inversion of InSAR, GPS, and Teleseismic Data

¹ Geosciences Azur CNRS/UNSA
Sophia Antipolis, France
 (B.D.)

² Institut for Geophysics
Zurich, Switzerland
 (J.S., D.G.)

³ Jet Propulsion Laboratory
Pasadena, California
 (P.L.)

The slip distribution of the 16 October 1999, M_w 7.1, Hector Mine earthquake, California, is investigated in space and time by jointly inverting geodetic data and broadband teleseismic data constrained by reported surface offsets. The geodetic data consist of a dense network of Global Positioning System (GPS) data and synthetic aperture radar (SAR) interferograms from both ascending and descending satellite tracks. Considering the complexity of the earthquake rupture, our fault model has four partially overlapping segments discretized into 3 x 3 km² patches. The seismic source parameters on each subfault are estimated using a nonlinear inversion scheme based on a simulated annealing method to explore the parameter space. We allow a variable rupture velocity and slip to vary in amplitude, direction, and duration. We first explore the space and time resolution of each data set and their combination with data synthetized from known slip distributions. We estimate the slip distribution from the different data sets inverted separately and finally perform a joint inversion of the combined data sets. The teleseismic data inversion exhibits a rather bad spatial resolution compared with the resolution power of the other data. The geodetic data nearly completely map the coseismic deformation field of the Hector Mine earthquake and strongly constrain the spatial distribution of the final slip and the fault geometry. The spatial resolution is expected to be best for the depth range of 0 to 10 km over the entire fault model. The joint inversion of both geodetic and seismic data provides a robust estimate of slip history that simultaneously fits the independent data sets in space and time. The Hector Mine earthquake is a right-lateral strike-slip event that presents a heterogeneous distribution of slip at shallow depth (<12 km). Most of the seismic moment is released in the vicinity of the hypocenter over two overlapping segments. The total seismic moment is 5.8·10¹⁹ N m (our joint inversion) with a peak displacement amplitude of about 6 m. The velocity rupture is comprised between 2 and 2.5 km/sec for a total duration of about 15 sec over an extent of about 50 km.

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