← Back to Gallery

Unsteady, Uniform Rupture Growth Revealed by Tectonic Tremors in Cascadia

Slow slip events (SSEs) in the Cascadia subduction zone are marked by tectonic tremors that track the migrating slip front. We cluster a catalog of 180,000 tremor epicenters into 1056 swarms and analyze the rupture of their underlying SSEs. Using new methods to measure both swarm area and duration, we find that all SSEs converge to a uniform growth pattern described by a single power-law, A(t) ~ Ktⁿ, with exponents that vary between 0.5 and 1.0 for larger, reliably fit events. This uniform SSE growth, however, is only apparent when we redact intermittent pauses in tremor activity. We suggest that these pauses reflect unsteady propagation of the slip front and excluding them removes rupture complexity to reveal a diffusive-like slip process and underlying universality in growth. These observations imply the propagation velocity, v_prop, may also be described by a power law ranging between ~ t^-3/4 and t^-1/2. Slip propagation starts relatively fast and slows as the rupture progresses by up to an order of magnitude for the largest events, which terminate at speeds of ~20-40 km/day. Notably, this process does not reset after a temporal pause, which implies an effective ‘memory’ or path-dependent evolution in the fault response to loading as the rupture grows. Our observations suggest all ruptures start and grow nearly identically, and their eventual size is not predetermined, but controlled by external factors.

Session: What Controls the Style of Fault Slip in Subduction Zones? I

Type: Oral

Room: Grand E-K

Date: 4/20/2022

Presentation Time: 03:00 PM Pacific

Presenting Author: Aaron Wech

Student Presenter: No

Additional Authors