Postseismic deformation following the 2004 Mw 6.0 Parkfield earth- quake: Is there the viscoelastic relaxation of the lower crust?
Speaker: Chi-Hsien Tang Adviser: Wu-Lung Chang
Abstract
The San Andreas Fault around Parkfield, California, exhibits a transition from a creeping segment to a locked segment. Six Mw 6.0 similar earthquakes had occurred repeatedly in this transition zone since 1881. The coseismic/postseismic deformation due to the 2004 Parkfield earthquake, the most recent event in a series, was well recorded by Global Positioning System (GPS) stations. Several studies (Barbot et al., 2009, 2012) have shown that postseismic deformation following this event is dominated by afterslip in the upper crust. However, below the main rupture area, some fraction of the afterslip inferred from kinematic inversion may be actually caused by viscoelastic relaxation of the lower crust. Bruhat et al. [2011] shows that even the trade-off between deep afterslip and viscoelastic relaxation is hard to determine, the deep-seated postseismic deformation could be explained by the ductile deformation in the lower crust as well. If the viscoelastic relaxation below 20 km depth is allowed, the variance reduction of the model could be slightly improved. On the other hand, Chang et al. [2013] derived a fully dynamic afterslip model from coseismic stress perturbation on the fault, which demonstrated that the deep afterslip is predicted within 548 days after the mainshock. The evidence for the presence of the viscoelastic relaxation of the lower crust beneath Parkfield, California remains uncertain, and worth to discuss as well.
References
Barbot, S., Y. Fialko, and Y. Bock (2009), Postseismic deformation due to the Mw 6.0 2004 Parkfield earthquake: Stress-driven creep on a fault with spatially variable rate-and-state friction parameters, J. Geophys. Res., 114, B07405.
<full text>
Barbot, S., N. Lapusta, and J.-P. Avouac (2012), Under the hood of the earthquake machine: Toward predictive modeling of the seismic cycle, Science, 336, 707–710.
<full text>
Bruhat, L., S. Barbot, and J.‐P. Avouac (2011), Evidence for postseismic deformation of the lower crust following the 2004 Mw 6.0 Parkfield earthquake, J. Geophys. Res., 116, B08401.
<full text>
Chang, S.-H., J.-P. Avouac, S. Barbot, and J.-C. Lee (2013), Spatially variable fault friction derived from dynamic modeling of aseismic afterslip due to the 2004 Parkfield earthquake, J. Geophys. Res. Solid Earth, 118, 3431–3447.