Emily Roland

Source and progression of a submarine landslide and tsunami: The 1964 Great Alaska earthquake at Valdez

Like many subduction zone earthquakes, the deadliest aspects of the 1964 M = 9.2 Alaska earthquake were the tsunamis it caused. The worst of these were generated by local submarine landslides induced by the earthquake. These caused high runups, engulfing several coastal towns in Prince William Sound. In this paper, we study one of these cases in detail, the Port Valdez submarine landslide and tsunami. We combine eyewitness reports, preserved film, and careful posttsunami surveys with new geophysical data to inform numerical models for landslide tsunami generation. We review the series of events as recorded at Valdez old town and then determine the corresponding subsurface events that led to the tsunami. We build digital elevation models of part of the pretsunami and posttsunami fjord-head delta. Comparing them reveals a ~1500 m long region that receded 150 m to the east, which we interpret as the primary delta landslide source. Multibeam imagery and high-resolution seismic reflection data identify a ~400 m wide chute with hummocky deposits at its terminus, which may define the primary slide path. Using these elements we run hydrodynamic models of the landslide-driven tsunamis that match observations of current direction, maximum inundation, and wave height at Valdez old town. We speculate that failure conditions at the delta front may have been influenced by manmade changes in drainage patterns as well as the fast retreat of Valdez and other glaciers during the past century.

Designing an offshore geophysical network in the Pacific Northwest for earthquake and tsunami early warning and hazard research

Every few hundred years, the Cascadia subduction zone off the coast of the Pacific Northwest hosts devastating earthquakes, and there is a growing awareness of the need to be prepared for these events. An offshore cabled observatory extending the length of the Cascadia subduction zone would enhance the performance of the earthquake and tsunami early warning systems, would enable real time monitoring and predictions of the incoming tsunami, and would contribute substantially to scientific research aimed at mitigating the hazard. The University of Washington has recently initiated a study to develop a conceptual design for the U.S. portion of an offshore observatory for earthquake and tsunami early warning and research. This paper presents the motivation for this work and plans for the study.