Regional Ground-Motion Effects from Intraslab Earthquakes in Northern Cascadia

Session: Forthcoming Updates of the USGS NSHMs: Hawaii, Conterminous U.S. and Alaska [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

We investigate regional ground-motion effects from intraslab earthquakes in northern Cascadia from data and ground-motion simulations. We developed an earthquake catalog of Mw>3.5 intraslab events that occurred between 2000 and 2019 and compiled a database of ground motions from seismic stations within 250 km epicentral distances. Ground motion processing returned 5-percent-damped pseudo-spectral accelerations at periods between 0.1 and 5 s, and residuals from the recorded ground motions are computed with respect to the NGA-Subduction ground motion model of Abrahamson et al. (2019). We partitioned the total residuals into between- and within-event terms and a bias term. Site terms were computed from all stations that recorded, at least, three earthquakes. At short periods (T<~0.5 s) the averaged site terms suggest that a band of persistent, relative amplification manifests within the Puget Lowland. To support the observational analysis, earthquake ground-motion simulations were carried out for point source focal mechanisms using the Cascadia community velocity model and the Hercules finite-element wave propagation code. A critical question for the region is the effect of the 3D seismic velocity structure on regional wave propagation and correspondingly for earthquake hazards, such as from slab-guided waves. Ground-motion patterns from the recorded and simulated ground motions will be compared.

Presenting Author: Morgan P. Moschetti

Authors