Repeating Earthquakes in the Cascadia Subduction Zone and Their Ties to Seismogenic Zone Heterogeneities

Date: 4/25/2019

Time: 09:15 AM

Room: Cascade II

The Cascadia Subduction Zone (CSZ) has long been noted to be seismically quiet, but paleoseismic studies indicate an active history of earthquakes up to M9. Given the potential of a future megathrust rupture, mapping high coseismic slip patches/strong asperities on the plate interface, as well as the downdip extent of the seismogenic zone, is imperative in order to best estimate expected ground motions and tsunami inundation potential for the high population centers along the margin. Because the seismogenic zone resides mostly offshore, we improve our detection capability by using the amphibious Cascadia Initiative (CI; 2011-2015) seismic array to identify small earthquakes (< M4) and map along-strike variations in frictional conditions on the plate interface.

We apply subspace detection to find our small events, using templates derived from existing earthquake catalogs. Preliminary results suggest aseismic subduction in the vicinity of a subducted seamount offshore central Oregon, while the central portion of the fault appears to be strongly locked with very little seismicity. At the Olympic Peninsula, a cluster of small events may suggest a change in the nearby asperity modeled for the M9 1700 event. Here we present new events recorded during the full CI experiment, and corresponding fault-zone heterogeneities delineated by their locations and source parameter analysis. We tie these interpretations to previous along-strike variations: the presence of the accreted crystalline Siletz terrane, the location of forearc basins, the 1700 M9 slip distribution model, and segment boundaries estimated from paleoseismic studies.

Presenting Author: Emily A. Morton

Authors