Quantifying the Role of 3D Fault Geometry Complexities on Slow and Fast Earthquakes

TL;DR

This study uses 3D simulations to show how complex fault geometries influence the occurrence of both slow slip events and earthquakes, highlighting the importance of fault interactions and geometry in seismic behavior.

Contribution

It introduces a new metric based on Coulomb stress to quantify fault interactions, revealing how geometry affects slip regimes and reproduces observed scaling laws.

Findings

Complex fault geometries can generate both slow and fast earthquakes.

Fault interaction strength determines slip regime occurrence.

Moment-duration scaling depends on event detection thresholds.

Abstract

Traditional models of slow slip events (SSEs) often oversimplify fault geometry, yet imaging studies show that real subduction faults are segmented and complex. We investigate how fault interactions influence slip behavior using 3D quasi-dynamic earthquake sequence simulations of two parallel faults with uniform rate-weakening friction, accelerated with hierarchical matrices. Our results identify four slip regimes-periodic earthquakes, coexisting SSEs and earthquakes, only SSEs, and complex sequences-while a single planar fault under the same conditions produces only earthquakes. We quantify fault interaction using the maximum Coulomb stress induced on a target fault by unit, spatially uniform stress drop on a neighboring fault. Because the source stress drop is normalized, the metric depends only on geometry and is independent of friction and nucleation length, and it can be extended to arbitrary fault configurations. The occurrence of SSEs is confined to an intermediate range of interaction strength. We also reproduce the observed moment-duration scaling and show that it depends on event detection thresholds. These results demonstrate that complex fault geometry can naturally generate both slow and fast earthquakes through evolving traction heterogeneities.