Change of apparent segmentation of the San Andreas fault around Parkfield from space geodetic observations across multiple periods
نویسندگان
چکیده
[1] Sequences of earthquakes are commonly represented as a succession of periods of interseismic stress accumulation followed by coseismic and postseismic phases of stress release. Because the recurrence time of large earthquakes is often greater than the available span of space geodetic data, it has been challenging to monitor the evolution of interseismic loading in its entire duration. Here we analyze large data sets of surface deformation at different key episodes around the Cholame, Parkfield and creeping segments of the San Andreas Fault that show evidence of significant deceleration of fault slip during the interseismic period. We compare the average fault slip rates before and after the 2004Mw 6 Parkfield earthquake, in the 1986–2004 and 2006–2012 periods, respectively, avoiding 2 years of postseismic deformation after 2004. Using a combination of GPS data from the Plate Boundary Observatory, the Southern California Earthquake Center Crustal Motion Map and the Bay Area Velocity Unification networks and interferometric synthetic aperture radar from the Advanced Land Observing Satellite (ALOS) and Envisat satellites, we show that the area of coupling at the transition between the Parkfield and Cholame segments appears larger later in the interseismic period than it does earlier on. While strong plate coupling is uniform across the Parkfield and Cholame segments in the 1986–2004 period, creep occurs south of the 2004 epicenter after 2006, making segmentation of the San Andreas Fault south of Parkfield more clearly apparent. These observations indicate that analyses of surface deformation late in the earthquake cycle may overestimate the area of plate coupling. A fault surface creeping much below plate rate may in some case be a region that does not promote earthquake nucleation but rather just be at a slower stage of its evolution. Our analysis also shows signs of large variation of slip velocity above and below plate rate in the creeping segment indicating that cycles of weakening and hardening can also be at play in dominantly aseismic areas.
منابع مشابه
Postseismic relaxation along the San Andreas fault at Parkfield from continuous seismological observations.
Seismic velocity changes and nonvolcanic tremor activity in the Parkfield area in California reveal that large earthquakes induce long-term perturbations of crustal properties in the San Andreas fault zone. The 2003 San Simeon and 2004 Parkfield earthquakes both reduced seismic velocities that were measured from correlations of the ambient seismic noise and induced an increased nonvolcanic trem...
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