Variation of Proportionality Between Stress Drop and Slip, With Implications for Megathrust Earthquakes

Abstract

Earthquake stress drop Δσ is related to fault slip via (Formula presented.), where μ, D, and Lc denote shear modulus, average slip, and fault dimension. C is controlled by the system geometry, characterizes the effective stiffness of the system, and is commonly assumed to be a constant near 1. We use 3D elastostatic models to systematically investigate how C is controlled by fault burial depth, dip angle, and slip direction. We find that C decreases with smaller burial depth and dip angle, with a value for a shallow-dipping surface-rupturing fault roughly one-fifth that of the deeply buried case. Our results help explain the apparent magnitude-dependent stress drops of megathrust earthquakes in Thingbaijam et al. (2017), https://doi.org/10.1785/0120150291. There may also be implications for the apparent depth- and magnitude-dependence in other source parameters, and for reducing uncertainties in the seismic and tsunami hazard assessments of megathrust earthquakes.