Sep 2023
Abstract
Understanding the mechanisms governing earthquake motion along faults is crucial for investigating earthquake nucleation, dynamic slip evolution, and arrest. Faults have complex geometries, including a fracture network within the damage zone characterized by a low-velocity zone. This dissertation aims to provide insights into the fundamental physics underlying cascading earthquakes in geometrically complex fault systems using 3D high-resolution dynamic rupture modeling. This is achieved by (i) developing physics-based numerical models that integrate geological observations, laboratory findings, statistical measurements, and theoretical insights, and (ii) utilizing these models to explore the influence of different physical mechanisms and conditions reflected in geological, geophysical, and geodetic observations. I investigate the dynamics of complex earthquake source mechanisms observed in the 2017 Mw 5.5 Pohang earthquake and develop a new fault plane fitting technique with a priori source parameters. The simulations successfully reproduce key observable characteristics of the earthquake, emphasizing the significance of perturbations in local stress conditions that lead to such an earthquake. I then construct a fracture network model comprising two intersecting families with a listric fault to examine the conditions that facilitate a self-sustained rupture cascade within the fracture network. The results demonstrate that a cascading rupture is mechanically plausible under high fracture connectivity if one fracture family is favorably oriented and the other conditionally or favorably oriented to ambient stress. The dynamic rupture cascade occurring within geometrically complex faults presents distinct ground motion characteristics compared to a non-cascading rupture. I conduct a comparative analysis of high-resolution models to investigate this phenomenon. The simulations feature high-frequency seismic waves generated by the simultaneous slipping of multiple fractures during a rupture cascade. Finally, I investigate dynamic rupture cascades in microearthquakes using a planar fault model and fracture networks within its damage zone. The analyses incorporate considerations of elastic and inelastic material properties and a low-velocity fault zone. The results highlight that, in microearthquakes, the propensity of failure for both the fractures and the main fault outweighs the importance of material properties.
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