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

TitleSeismic and geodetic evidence for extensive, long-lived fault damage zones
Publication TypeJournal Article
Year of Publication2009
AuthorsCochran ES, Li Y-G, Shearer PM, Barbot S, Fialko Y, Vidale JE
JournalGeology
Volume37
Pagination315-318
Date PublishedApr
ISBN Number0091-7613
Accession NumberWOS:000264753700007
Abstract

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 findings 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.