Summary: Differences in the evolution of seismic velocities
after the San Simeon and the Parkfield earthquakes
indicate that two different physical mechanisms may
be responsible for the changes in crustal properties: (i)
damage of shallow layers and fault zone caused by
the strong ground shaking and (ii) co-seismic stress
change followed by the postseismic relaxation. These
results demonstrate that measuring small velocity per-
turbations from correlations of seismic noise can be a
useful tool for studying the continuous time evolution
of the stress regime in the vicinity of seismogenic faults.
References and Notes
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Seismol. Soc. Am. 93, 854 (2003).
4. F. Niu, P. G. Silver, T. M. Daley, X. Cheng, E. L. Majer,
Nature 454, 204 (2008).
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Science 307, 1615 (2005).