Thursday, December 7, 2017 - 15:00, room The John Swallow room (Room number: 054/06)
Speaker: Prof. Alexander Ray Simms from UC Santa Barbara
Searching For Tsunamis along the California Coast
The devastating impacts of recent tsunami in Sumatra, Chile, and Japan have sparked renewed interest in examining the tsunami risks along other coastlines. Northern California is known to have experienced great (M>8) earthquakes and resulting tsunamis due to its location over the Cascadia Subduction Zone. We review the impacts these tsunami had on the beaches of northern California. In addition to these hazards for northern California, recent work has suggested that local structures within the Southern California Borderlands also generated large (>3 m) tsunami. We report on efforts to find evidence for these hypothesized tsunami within the estuaries and beaches of Southern California. Although we have yet to find evidence for marine washover beds dating to the time of the proposed large tsunami within any of the 5 estuaries studied, we do find clear signals of an extended stormy period in 1861-1862. This stormy winter, thought to have resulted from a series of atmospheric river storms, created washover fans comparable in scale to hurricane and tsunami fans reported across the globe. Similar beds not dating to the periods of proposed large earthquakes suggest this stormy period was not an isolated event but a reoccurring hazard along the California Coast. We also report evidence for a period of rapid co-seismic subsidence within one of these fault-bound estuaries along the southern California Coast. This subsidence event suggests that hazards associated with co-seismic subsidence are not confined to estuaries along subduction zones but are a real threat to any fault-bound estuary.