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

Abstract

Abstract Earthquake stress drop Δσ is related to fault slip via Δσ=C⋅μ⋅DLc, 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.

Keywords

• earthquake scaling relation
• earthquake source processes
• megathrust earthquakes
• free surface effects
• crack model
• proportionality factor C