Fault-size dependent fracture energy explains multi-scale seismicity and cascading earthquakes

TL;DR

This paper introduces a fracture energy scaling law based on fault size that explains the multi-scale nature of seismicity and cascading earthquakes, integrating observations with physics-based modeling.

Contribution

It proposes a new linear scaling relationship for fracture energy in small earthquakes and demonstrates how multi-scale fracture cascades can trigger large earthquakes.

Findings

Small-slip fracture energy scales linearly with fault size.

Multi-scale fracture cascades can dynamically trigger large earthquakes.

The model explains seismicity across all scales.

Abstract

Earthquakes vary in size over many orders of magnitude, yet the scaling of the earthquake energy budget remains enigmatic. We propose that fundamentally different "small-slip" and "large-slip" fracture processes govern earthquakes. We combine seismological observations with a physics-based mechanical earthquake model under flash-heating friction. We find that dynamic weakening and restrengthening effects are non-negligible in the energy budget of small earthquakes and establish a simple linear scaling relationship between small-slip fracture energy and fault size. We use supercomputing to apply this scaling and unveil volumetric "Mode-4" earthquake cascades involving $>700$ multi-scale fractures within a fault damage zone, capable of dynamically triggering large earthquakes. Our findings provide an intuitive explanation of seismicity across all scales with important implications for comprehending earthquake nucleation and multi-fault rupture cascades.