Project Abstract
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We investigate the role of heterogeneous stress in slip nucleation and dynamic rupture. In our models, slip nucleates where the ratio of shear stress to effective normal stress is ~ 0.7 but propagates into regions where that ratio is ~ 0.2. 2D numerical simulations with thermal pressurization produce behavior observed in natural earthquakes. We consider two idealized nucleation conditions: one "high stress" in which effective normal stress is uniform and shear stress locally increases with time, the another "low strength" in which shear stress is uniform but effective normal stress locally decreases. In high-stress ruptures, thermal pressurization is substantial within the nucleation zone and can produce self-sustaining ruptures that propagate far into low stress regions. Longer run-outs occur for larger background shear stress; arresting ruptures are pulse-like. Sustained ruptures tend to be “crack-like,” with slip continuing behind the rupture tip. In low-strength ruptures, thermal pressurization is modest within the nucleation zone, but becomes significant as slip propagates. In arresting ruptures, slip stops from the tip inward in a crack-like manner. At higher background stress crack-like ruptures sustained by thermal pressurization are possible, but the threshold background stress for sustained rupture is higher than for high-stress nucleation. For arresting ruptures in either mode, stress drops are ~ 10MPa. Low-strength ruptures produce a moment-length relationship consistent with crack models, while the slip pulses resulting from high-strength nucleation do not. These results show that the magnitude of thermal pressurization within the nucleation zone strongly influences the behavior of the ensuing dynamic rupture. |
