Localizing Interseismic Deformation With Far-Field Loading Around Locked Strike-Slip Faults

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Localization of interseismic deformation around locked strike-slip faults is widely observed. The fault-parallel velocity is usually modelled by imposing full-rate creep directly below the locking depth. Here we study how localization may occur under far-field tectonic loading without this imposed creep. The Earth can be represented by an elastic lithosphere overlying a viscoelastic asthenosphere. We demonstrate that under end-member conditions the viscoelastic model can be further simplified into equivalent elastic models. For example, the elastic half-space model simulates an unrelaxed asthenosphere (at the beginning of the far-field loading), while the elastic plate model represents a fully relaxed asthenosphere (after many Maxwell times). Therefore, we can use elastic models to study to what degree far-field loading can cause the localization under these conditions. We find that the strike-length and continuity of locking is a key factor. With infinite locking length, little localization occurs in a plate model under any condition. The presence of a weak zone below the locking depth only slightly enhances localization, even in a half space. We show that in a more realistic situation, creeping segments may cause significant localization to adjacent locked segments. The results indicate, for example, localized deformation around the Carrizo segment of the San Andreas Fault is likely associated with its neighboring creeping segment. In addition, we examine the influence of previous earthquakes using viscoelastic models. If earthquake rupture is kinematically imposed to keep pace with long-term fault slip rate, as in the vast majority of earthquake cycle models, numerous earthquakes serve to develop a zone of viscous shear below the locking depth. Our results suggest that this is almost equivalent to imposing full-rate creep below the locking depth. Localization of deformation in a viscoelastic Earth with neither deep creep nor seismic rupture imposed is still an unresolved problem.

Presenting Author: Yijie Zhu

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