[Withdrawn] Surface-Wave Induced Dynamic Stresses on Arbitrary Faults in a Layered Earth

Date: 4/26/2019

Time: 04:30 PM

Room: Vashon

Propagating Rayleigh and Love waves from large earthquakes generate considerable dynamic stresses in the Earth’s crust, even in the far field. These stresses occasionally exceed empirical triggering thresholds on faults that are presumed to be critically stressed. Both volumetric and deviatoric stress variations in these dynamic stress tensors can affect the normal stress on a given fault, while shear stress variations on the fault are a result from transient deviatoric stresses from both types of surface waves, which often act on the fault at the same time.

Reports of potentially dynamically triggered tremor or earthquakes on a given fault are frequently accompanied by estimates of dynamic stresses on this fault. However, these reports do either not consider vertical variations in surface-wave displacements or assume a homogeneous crust. Estimates of the variations of dynamic stresses with back-azimuth typically do not include the effects of radiation patterns controlled by varying source mechanisms and depths.

To complement these estimates we calculate full dynamic stress tensors from 3-D and 3-C surface-wave displacement fields for a realistic Earth model. We test our approach on simulated data from the September 8, 2017, Mw 8.2 earthquake near the coast of Chiapas in Mexico. We quantify and visualize spatiotemporal variations in the isotropic stresses and principal stresses from the deviatoric stress tensors.

We then project these stresses onto the San Andreas fault and observe that 1) stresses generated at mid- and lower-crustal depths, where triggered events occur, are as large as and occasionally larger than those at the surface, 2) the maximum dynamic stress at these depths is reached at different times than peak ground velocity at the surface, which is used as a proxy for stress, 3) Combined stresses from simultaneous Rayleigh and Love waves create complex dynamic stress histories, 4) The off-shore Chiapas earthquake’s Love waves generated larger stresses on the San Andreas fault than its Rayleigh waves.

Presenting Author: Boris Roesler

Authors