Contemporary Cascadia Deformation overDisparate Time Scales: Systematics of Slow Earthquakes and Fore-arc Impingement

Central Washington University, Ellensburg WA

Investigators

Abstract

Continuous observations using Global Positioning System (GPS) geodesy yield high-precision determination of horizontal and vertical deformation rates and their variation in time and space. This project focuses on two aspects of the current GPS-determined four-dimensional deformation field along the Cascadia convergent margin in the Pacific Northwest. First, the spatial and temporal distribution of transient events on the Cascadia megathrust is being investigated. This part of the study is motivated by preliminary results that indicate at least 8 silent earthquakes (aseismic slip events lasting days to months) with Mw > 6.0 (equivalent) occurred in the Pacific Northwest since 1992 based on analysis of the PANGA network. The data are being reanalyzed using principal component analysis the results of which are used for spatial inversion to determine the moment yield, spatial locations, and migration of each creep event across the plate interface. Second, the kinematics of the migrating continental fore-arc (western Washington) as it encounters a rigid buttress (Vancouver Island) are being examined by analysis of the velocity field from the PANGA array, and development of fault geometry and mechanical block models of the intraplate deformation of the Cascadia margin and Puget Lowlands.