Stress Heterogeneity and Slip Complexity due to Fault Zone Damage in Fully Dynamic Earthquake Cycles

Prithvi Thakur, & Yihe Huang

Published August 13, 2019, SCEC Contribution #9490, 2019 SCEC Annual Meeting Poster #166 (PDF)

Mechanical modeling of fault-slip over long timescales is of fundamental importance for understanding earthquake physics and assessing seismic hazard. Mature strike-slip faults are usually surrounded by a narrow zone of damaged rocks characterized by low seismic wave velocities. Observations of earthquakes along such faults indicate that seismicity is highly concentrated within this damaged fault zone. However, the long-term influence of this damaged zone, i.e., decades to hundreds of years, is not well understood. We model aseismic slip and fully dynamic earthquake rupture propagation on a vertical strike-slip fault surrounded by a damaged fault zone for multiple earthquake sequences. We use observations along major strike-slip faults, e.g., San Andreas and Calico faults, to constrain the material properties and geometry of the damaged fault zone. We use a spectral-element method in two dimensions with a rate-state dependent friction along the fault to solve the equations of motion along a fault with depth-dependent variables. We show that dynamic wave reflections can have significant effects on producing stress heterogeneities that persist through multiple earthquake sequences and produce complexity in the earthquake sequence. In the presence of an elastic damaged zone with sharp velocity contrast, large earthquake rupture propagates as slip pulses due to wave reflections from the damaged zone boundaries. The largest M7 earthquake in each cycle is followed by a gap in intermediate-magnitude earthquakes and a log-linear distribution of smaller earthquakes. Our fully dynamic cycle simulations reveal the relation between the magnitude-frequency distribution and the width of the damage zone as well as the effect of the depth extent of damaged zone on constraining the hypocenter of earthquakes.

Key Words
Damage Zones, Seismology, Mechanics, Earthquake Cycles

Citation
Thakur, P., & Huang, Y. (2019, 08). Stress Heterogeneity and Slip Complexity due to Fault Zone Damage in Fully Dynamic Earthquake Cycles. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)