Moment release rate of Cascadia tremor constrained by GPS

Abstract

A comparison of GPS and seismic analyses of 23 distinct episodic tremor and slip events, located throughout the Cascadia subduction zone over an 11‐year period, yields a highly linear relationship between moment release, as estimated from GPS, and total duration of nonvolcanic tremor, as summed from regional seismic arrays. The events last 1–5 weeks, typically produce ∼5 mm of static forearc deformation, and show cumulative totals of tremor that range from 40 to 280 h. Moment released by each event is estimated by inverting GPS‐measured deformation, which is sensitive to all rates of tremor‐synchronous faulting, including aseismic creep, for total slip along the North American‐Juan de Fuca plate interface. Tremor, which is shown to be largely invariant in amplitude and frequency content both between events and with respect to its duration, is quantified using several different parameterizations that agree to within 10%. All known Cascadia events detected since 1997, which collectively span the Cascadia arc from northern California to Vancouver Island, Canada, release moment during tremor at a rate of 5.2 ± 0.4 × 1016 N m per hour of recorded tremor. This relationship enables estimation of moment dissipation, via seismic monitoring of tremor, along the deeper Cascadia subduction zone that poses the greatest threat to its major metropolitan centers.