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- Title
Impact Versus Frictional Earthquake Models for High‐Frequency Radiation in Complex Fault Zones.
- Authors
Tsai, Victor C.; Hirth, Greg; Trugman, Daniel T.; Chu, Shanna X.
- Abstract
Earthquakes occur within complex fault zones containing numerous intersecting fault strands. This complexity poses a computational challenge for rupture models, which typically simplify fault structure to a small number of rough fault surfaces, with all other deformation assumed to be off‐fault viscoplastic deformation. In such models, high‐frequency ground motions originate solely from frictionally mediated, heterogeneous slip on a small number of potentially rough fault surfaces or from off‐fault viscoplastic deformation. Alternative explanations for high‐frequency ground motion generation that can account for a larger number of fault surfaces remain difficult to assess. Here, we evaluate the efficacy of a recently proposed stochastic impact model in which high‐frequency ground motion is caused by elastic impacts of structures within a complex fault zone. Impacts are envisioned to occur in response to fault motion in the presence of geometrical incompatibilities, which promotes transfer of slip onto different fault strands on timescales mediated by elasticity. We investigate the role of a complex fault zone for high‐frequency ground motion by comparing the underlying assumptions and resulting predictions of impact and rough fault frictional models. Relative to rough fault frictional models, impact models are characterized by deformation timescales and corner frequencies that are set by elasticity rather than viscoplasticity, relatively angular rather than smoothly varying fault roughness geometries, high‐frequency radiation patterns that are more isotropic, and higher P/S radiated energies. We outline ways to discriminate whether impact or rough fault frictional models are more likely to explain observations of high‐frequency ground motions. Plain Language Summary: Why are some earthquakes of the same size gentler and some of them more destructive? It is known that earthquakes usually occur in fault zones with many intersecting faults, but most models that attempt to explain the variability in destructiveness assume that earthquakes occur on a single fault surface. Here, we consider how the complex interactions between structures within a fault zone with many fault surfaces may contribute to the damaging jerky ground motions. Collisions between discrete fault blocks are envisioned to occur to allow large‐scale sliding that is needed to occur during an earthquake. We find that the nature of ground motions from such collisions depends on the sizes and geometries of the blocks, that the spatial variability in ground motions depends on the orientation of the collisions, and that different waves are excited differently by collisions as compared with the shearing motions typically assumed for earthquakes. We compare the collision model with more standard models of earthquakes and discuss how the predicted differences may be used along with certain earthquake observations to distinguish between the models. Key Points: We compare the predicted earthquake ground motions from elastic impacts in a complex fault zone with predictions from frictional modelsGround motions from elastic impacts are caused by the size and shape of fault‐zone structures instead of by off‐fault viscoplastic parametersHigh‐frequency ground motions from elastic impacts are more isotropic and have higher P/S radiated energies
- Subjects
EARTHQUAKES; FAULT zones; SURFACE fault ruptures; VISCOPLASTICITY; STOCHASTIC analysis
- Publication
Journal of Geophysical Research. Solid Earth, 2021, Vol 126, Issue 8, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB022313