Untangling Slab Geometry's Influences on the Megathrust Earthquake Cycle
Description:
Across disparate tectonic settings, fault geometry plays a fundamental role in determining earthquake characteristics such as magnitude, rupture area, spatial distribution, radiated frequency content, and average recurrence interval. In subduction zones, observations of both slow and fast slip transients have led to proposals that aspects of megathrust fault geometry such as roughness or dip control the locations and slip behavior of slow-slip events, tremor, (very-)low-frequency earthquakes and large megathrust ruptures. Correlations between the magnitude and megathrust geometry of recorded Mw > 8.5 earthquakes suggest that larger events tend to rupture flatter, more shallowly dipping subduction interfaces with wider downdip seismogenic zones. However, the mechanisms and relative importance of these apparent geometric controls on maximum magnitude remain elusive. Here, we analyze the specific mechanisms and relative contributions of megathrust dip and curvature using self-consistent 2D discontinuous Galerkin finite-element models of sequences of earthquakes and aseismic slip. Our results suggest that the downdip seismogenic width and average slab dip determine the maximum possible earthquake magnitude for a given subduction zone, while sharper slab curvature increases megathrusts’ rupture variability and reduces their tendency to slip in maximal events. These models support the hypothesis that increased megathrust geometric heterogeneity promotes rupture variability and more frequent smaller partial ruptures by enhancing interseismic strength and stress variability on the fault interface. This relationship between fault geometry and rupture variability suggests that a subduction zone’s tendency to host full-margin ruptures may be limited by geometric heterogeneities like rough subducting seafloor or sharp variations in slab curvature, highlighting the importance of high-resolution imaging of these features.
Session: From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia
Type: Oral
Date: 4/20/2023
Presentation Time: 02:00 PM (local time)
Presenting Author: James Biemiller
Student Presenter: No
Invited Presentation:
Authors
James Biemiller Presenting Author Corresponding Author jbiemiller@usgs.gov U.S. Geological Survey |
Lydia Staisch lstaisch@usgs.gov US Geological Survey |
Alice-Agnes Gabriel algabriel@ucsd.edu University of California, San Diego |
Dave May dmay@ucsd.edu University of California, San Diego |
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Untangling Slab Geometry's Influences on the Megathrust Earthquake Cycle
Category
From Earthquakes to Plate Boundaries: Insights Into Fault Behavior Spanning Seconds to Millennia