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Insight Into Depth Variations in Effective Stress and Fault Strength From Geodynamic-Seismic Cycle and Earthquake Dynamic Rupture Modeling

Description: 

The local stress regime and fault strength together exert first order control on fault mechanics and earthquake rupture dynamics. However, these characteristics remain elusive, especially at the level of detail desirable for initiating numerical simulations of large earthquakes on complex fault networks, which now are computationally possible. Linking between a geodynamic-seismic cycling model and a dynamic earthquake rupture model suggests that the effective stress field near a fault and the static and dynamic fault strength vary non-linearly with depth and are materially dependent. We present two model scenarios that contrast earthquakes resulting from (1) these heterogeneous initial conditions and (2) more commonly used, simpler initial conditions. Although the maximum fault strength is similar in both scenarios, the heterogeneous initial conditions in (1) result in larger fault slip, but lower average dynamic stress drop and lower rupture velocity. In addition, we observe that seismic waves traveling through complex materials around the fault in (1), as opposed to the homogeneous material in (2), influence earthquake rupture style and shallow slip accumulation. In both scenarios, the pore fluid pressure (Pf) increases linearly with depth. We further share how fault mechanics and earthquake dynamics are influenced by a simple change in the linear variation of Pf from sublithostatic to lithostatic, in which Pf is slightly less than, but constantly offset from, the lithostatic stress. If Pf follows a sublithostatic gradient, then pre-earthquake effective normal stress increases with depth. If Pf follows the lithostatic gradient, then normal stress is relatively constant with depth. As a result, a lithostatic Pf gradient moves peak slip and peak slip rate up-dip, and produces a more constant stress drop across the megathrust. These insights underscore the need to better understand initial earthquake conditions from a variety of sources, including collaborative modeling, in order to advance our understanding of earthquake initial conditions, fault strength and earthquake behavior.

Session: Characteristics and Mechanics of Fault Zone Rupture Processes, from Micro to Macro Scales - II

Type: Oral

Date: 5/2/2024

Presentation Time: 11:00 AM (local time)

Presenting Author: Elizabeth

Student Presenter: No

Invited Presentation: Yes

Authors