Strain accumulation across strike-slip faults: Investigation of the influence of laterally varying lithospheric properties
Abstract
We use boundary element methods to develop earthquake cycle models consisting of faulting in an elastic plate with possibly different thickness and rigidity on either side of the fault overlying a viscoelastic substrate. We show that isolate plate models that neglect the coupling of the plate to the underlying substrate might significantly overpredict the asymmetry in deformation across the fault. We also show a low-viscosity channel that exists within lower crust could significantly contribute to the asymmetry. We investigate the Carrizo segment of the San Andreas fault where it has been debated whether the rigidity contrast or thickness difference between the elastic layers (i.e. lithospheric layers) to the southwest and to the northeast of the fault is responsible for observed asymmetry in the GPS velocity profile across the fault. Through a fully probabilistic scheme, we invert 1994~2003 GPS data for the long-term slip rate, thicknesses of elastic layers, fault locked depth, rigidity ratio of the two elastic layers, stress relaxation time and earthquake recurrence using geological and geophysical constraints. We find that the inversion favors a thicker layer on east side (2 times) but stiffer layer on west side (1.4 times); however, uniform thickness and stiffness cannot be ruled out. We estimate a fault locking depth of 8-20 km, but the earthquake recurrence time and mantle relaxation time are not resolved. We also investigate the Renun segment of the Sumatra fault where the 1989-1996 GPS velocity profile across the fault is distinctly asymmetric. Inversion results show the elastic layer on the east side must be stiffer than the west side but the elastic thicknesses are not resolvable. We estimate a fault locking depth of 3-27 km, but the earthquake recurrence time and mantle relaxation time are not well resolved, either. We also investigate the segment of Altyn Tagh fault, the northern border of the Tibetan plateau between the Tarim and the Qaidam basins, where surface velocity (projected to fault-parallel direction) obtained from a stack of 15 interferograms using ERS and ENVISAT radar data covering the 1995-2006 period is distinctly asymmetric. We examine the possibility of the existence of low-viscosity lower crust (a channel) in the Tibetan plateau which has been debated. We find that the inversion result shows the northern elastic layer (Tarim Basin) must be stiffer and thicker than the southern one (Tibetan Plateau) but the viscosity of the mid-custal Tibetan channel in not resolvable. We estimate a fault locking depth of 8.5-12.5 km, the earthquake recurrence time of 550-1300 yrs, and a mantle relaxation time of 140-600 yrs.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.T53C2149H
- Keywords:
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- 8118 TECTONOPHYSICS / Dynamics and mechanics of faulting;
- 8159 TECTONOPHYSICS / Rheology: crust and lithosphere