Active Protothrusts and Fluid Highways: Seismic Noise Reveals Hidden Subduction Dynamics in Cascadia

TL;DR

This study uses a decade of seismic data from Cascadia to reveal how fluid migration and fault interactions influence subduction zone dynamics, including locking, slow slip events, and earthquake stability.

Contribution

It introduces new insights into subduction zone behavior by linking seismic noise patterns to fluid migration and fault interactions in Cascadia.

Findings

Northern Cascadia is fully locked with strain accumulation.

Central Cascadia shows slow slip events and fluid migration.

Fluid transport likely stabilizes large earthquakes.

Abstract

Complex interactions between strain accumulation, fault slip, and fluid migration influence shallow subduction zone dynamics. Using a decade of continuous ambient seismic data from Cascadia seafloor observatories, we identified distinct regional variations in subduction dynamics. Northern Cascadia exhibits a fully locked megathrust with persistent strain accumulation, while central Cascadia displays a slow slip event on protothrusts and rapid fluid migration along fault systems in the overriding plate. Effective fluid transport through the decollement and the Alvin Canyon Fault likely modulates the earthquake behavior but does not cause slow slip events on the megathrust and likely stabilizes large earthquakes, promoting rupture arrest.