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Science 13 September 2002:
Vol. 297. no. 5588, pp. 1858 - 1862
DOI: 10.1126/science.1074671
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Reports

Deformation on Nearby Faults Induced by the 1999 Hector Mine Earthquake

Yuri Fialko,1* David Sandwell,1 Duncan Agnew,1 Mark Simons,2 Peter Shearer,1 Bernard Minster1

Interferometric Synthetic Aperture Radar observations of surface deformation due to the 1999 Hector Mine earthquake reveal motion on several nearby faults of the eastern California shear zone. We document both vertical and horizontal displacements of several millimeters to several centimeters across kilometer-wide zones centered on pre-existing faults. Portions of some faults experienced retrograde (that is, opposite to their long-term geologic slip) motion during or shortly after the earthquake. The observed deformation likely represents elastic response of compliant fault zones to the permanent co-seismic stress changes. The induced fault displacements imply decreases in the effective shear modulus within the kilometer-wide fault zones, indicating that the latter are mechanically distinct from the ambient crustal rocks.

1 Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA.
2 Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 USA.
*   To whom correspondence should be addressed. E-mail: fialko{at}radar.ucsd.edu.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)