Seismic and geodetic evidence for extensive, long-lived fault damage zones

During earthquakes, slip is often localized on preexisting faults, but it is not well understood how the structure of crustal faults may contribute to slip localization and energetics. Growing evidence suggests that the crust along active faults undergoes anomalous strain and damage during large earthquakes. Seismic and geodetic data from the Calico fault in the eastern California shear zone reveal a wide zone of reduced seismic velocities and effective elastic moduli. Using seismic traveltimes, trapped waves, and interferometric synthetic aperture radar observations, we document seismic velocities reduced by 40%‐ 50% and shear moduli reduced by 65% compared to wall rock in a 1.5-km-wide zone along the Calico fault. Observed velocity reductions likely represent the cumulative mechanical damage from past earthquake ruptures. No large earthquake has broken the Calico fault in historic time, implying that fault damage persists for hundreds or perhaps thousands of years. These fi ndings indicate that faults can affect rock properties at substantial distances from primary fault slip surfaces, and throughout much of the seismogenic zone, a result with implications for the amount of energy expended during rupture to drive cracking and yielding of rock and development of fault systems.

[1]  Y. Fialko.  Probing the mechanical properties of seismically active crust with space geodesy: Study of the coseismic deformation due to the 1992 Mw7.3 Landers (southern California) earthquake , 2004 .

[2]  D. Sandwell,et al.  Effect of a compliant fault zone on the inferred earthquake slip distribution , 2008 .

[3]  K. Sieh,et al.  Long dormancy, low slip rate, and similar slip-per-event for the Emerson fault, eastern California shear zone , 1997 .

[4]  Y. Ben‐Zion,et al.  High-resolution imaging of the Bear Valley section of the San Andreas fault at seismogenic depths with fault-zone head waves and relocated seismicity , 2005 .

[5]  J. Vidale,et al.  Seismic Evidence for Rock Damage and Healing on the San Andreas Fault Associated with the 2004 M 6.0 Parkfield Earthquake , 2005 .

[6]  J. C. Savage,et al.  The velocity field along the San Andreas Fault in central and southern California , 1991 .

[7]  Paul A. Rosen,et al.  Transient strain accumulation and fault interaction in the eastern California shear zone , 2001 .

[8]  John E. Vidale,et al.  Damage to the shallow Landers fault from the nearby Hector Mine earthquake , 2003, Nature.

[9]  T. Moser.  Shortest path calculation of seismic rays , 1991 .

[10]  Y. Fialko.  Fracture and Frictional Mechanics: Theory , 2007 .

[11]  Yehuda Bock,et al.  Near real‐time radar interferometry of the Mw 7.1 Hector Mine Earthquake , 2000 .

[12]  Bernard Minster,et al.  Deformation on Nearby Faults Induced by the 1999 Hector Mine Earthquake , 2002, Science.

[13]  Qizhi Chen,et al.  Geodetic Evidence for a Near-Fault Compliant Zone along the San Andreas Fault in the San Francisco Bay Area , 2002 .

[14]  Yehuda Ben-Zion,et al.  A shallow fault-zone structure illuminated by trapped waves in the Karadere–Duzce branch of the North Anatolian Fault, western Turkey , 2003 .

[15]  G. Nolet,et al.  Traveltimes and amplitudes of seismic waves: a re-assessment , 2013 .

[16]  Discontinuity of the Mozumi-Sukenobu fault low-velocity zone, central Japan, inferred from 3-D finite-difference simulation of fault zone waves excited by explosive sources , 2004 .

[17]  K. Olsen,et al.  Fault zone amplified waves as a possible seismic hazard along the Calaveras Fault in central California , 2001 .

[18]  Roy K. Dokka,et al.  Late Cenozoic strike-slip faulting in the Mojave Desert, California , 1990 .

[19]  L. Owen,et al.  Paleoseismologic evidence for multiple Holocene earthquakes on the Calico fault: Implications for earthquake clustering in the Eastern California shear zone , 2010 .

[20]  Hongfeng Yang,et al.  High-resolution structures of the Landers fault zone inferred from aftershock waveform data , 2006 .

[21]  Xu,et al.  Evidence of shallow fault zone strengthening after the 1992 M7.5 landers, california, earthquake , 1998, Science.

[22]  Thomas K. Rockwell,et al.  Paleoseismology of the Johnson Valley, Kickapoo, and Homestead Valley Faults: Clustering of Earthquakes in the Eastern California Shear Zone , 2000 .

[23]  Dylan Blumentritt,et al.  Slip rate of the Calico fault: Implications for geologic versus geodetic rate discrepancy in the Eastern California Shear Zone , 2007 .