Department of Earth and Environmental Science

Constraining past mega-thrust Earthquake-induced vertical land movement in the pacific northwest

Perhaps no single natural phenomenon affects the lives of people along the Pacific Northwest and around the Pacific Rim as much as earthquakes.  Continuing subduction of the Juan de Fuca plate beneath the North American plate constitutes a major seismic hazard.  In contrast to Alaska, no written sources record plate-boundary earthquakes in this region during the last 200 years. However, geological evidence suggests repeated plate boundary earthquakes in the Cascadia subduction zone during the mid and late Holocene. Relative sea-level changes accompanying these earthquakes are described by an earthquake deformation cycle of rapid coseismic deformation during plate-boundary rupture followed by gradual interseismic strain typically lasting hundreds of years.

Previous work provides strong support for microfossil techniques as a means to assess the magnitude of submergence or coseismic subsidence, which accompanies marsh drowning. 

We aim to compile existing data and develop the first regional transfer function to quantify the spatial extent and magnitude of coseismic subsidence in the Cascadia subduction zone associated with the 1700 AD earthquake.  This will provide important information to (a) reduce the uncertainty regarding estimates of the location, magnitude and likelihood of future earthquakes; (b) better understand the importance of non-seismic factors (eustacy and isostacy) and seismic factors (coseismic subsidence and interseismic strain) in influencing land and sea-level movement; and (c) use paleoseismic data and relative sea-level data to constrain geophysical models of the Pacific Northwest.

Publications

Hawkes, A. D., Scott, D. B.  and Lipps, J. H. 2005. Evidence for possible precursor events of mega-thrust earthquakes on the west coast of North America. GSA Bulletin.