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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, B03307, doi:10.1029/2003JB002756, 2004

Probing the mechanical properties of seismically active crust with space geodesy: Study of the coseismic deformation due to the 1992 M w 7.3 Landers (southern California) earthquake

Yuri Fialko

Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


Abstract

The coseismic deformation due to the 1992 M w 7.3 Landers earthquake, southern California, is investigated using synthetic aperture radar (SAR) and Global Positioning System (GPS) measurements. The ERS-1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components (east, north, up) of the coseismic surface displacement field. The coseismic displacement field exhibits symmetries with respect to the rupture plane that are suggestive of a linear relationship between stress and strain in the crust. Interferometric synthetic aperture radar (InSAR) data show small-scale deformation on nearby faults of the Eastern California Shear Zone. Some of these faults (in particular, the Calico, Rodman, and Pinto Mountain faults) were also subsequently strained by the 1999 M w 7.1 Hector Mine earthquake. I test the hypothesis that the anomalous fault strain represents essentially an elastic response of kilometer-scale compliant fault zones to stressing by nearby earthquakes [ Fialko et al., 2002 ]. The coseismic stress perturbations due to the Landers earthquake are computed using a slip model derived from inversions of the InSAR and GPS data. Calculations are performed for both homogeneous and transversely isotropic half-space models. The compliant zone model that best explains the deformation on the Calico and Pinto Mountain faults due to the Hector Mine earthquake successfully predicts the coseismic displacements on these faults induced by the Landers earthquake. Deformation on the Calico and Pinto Mountain faults implies about a factor of 2 reduction in the effective shear modulus within the ∼2 km wide fault zones. The depth extent of the low-rigidity zones is poorly constrained but is likely in excess of a few kilometers. The same type of structure is able to explain high gradients in the radar line of sight displacements observed on other faults adjacent to the Landers rupture. In particular, the Lenwood fault north of the Soggy Lake has likely experienced a few centimeters of left-lateral motion across <1-km-wide compliant fault zone having the rigidity reduction of more than a factor of 2. The inferred compliant fault zones are interpreted to be a result of extensive damage due to past earthquakes.

Received 22 August 2003; accepted 3 February 2004; published 23 March 2004.

Index Terms: 1242 Geodesy and Gravity: Seismic deformations (7205); 1243 Geodesy and Gravity: Space geodetic surveys; 7209 Seismology: Earthquake dynamics and mechanics; 7215 Seismology: Earthquake parameters; 7260 Seismology: Theory and modeling.

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Citation: Fialko, Y. (2004), Probing the mechanical properties of seismically active crust with space geodesy: Study of the coseismic deformation due to the 1992 M w 7.3 Landers (southern California) earthquake, J. Geophys. Res., 109, B03307, doi:10.1029/2003JB002756.