Speaker: Angeliki Barberopoulou, Earth and Space Sciences
Title:
Time: 3:30 PM, Wednesday, 11/10/04
Place: Guggenheim Room 408d
Abstract:
Seismic waves from the Mw 7.9 Denali, Alaska, earthquake of 3 November, 2002, initiated a series of water waves that damaged at least 20 houseboats along the shores of Lake Union and Portage Bay in Seattle, caused large water waves in nearby Lake Washington, and caused numerous swimming pools in the Seattle area to slosh over their sides in Washington State, at an epicentral distance of 2400 km (Barberopoulou et al., 2004). These water waves occurred on a calm day at the approximate arrival time of the surface waves from the Denali earthquake. The houseboats are routinely subjected to waves from large ships and windstorms, so the damage during the earthquake suggests the generation of waves with unusual amplitudes or periods. These water waves were apparently initiated by large seismic surface waves directed along the west coast of North America by the source mechanism (Cassidy, 2003; Barberopoulou et al., 2004).
The damage from seiches during past teleseisms and deep local events has been minor in Washington State, but the local amplification of long period waves by sedimentary basins could make urban areas in the Puget Lowland vulnerable to high amplitude water waves during large earthquakes on local crustal faults or on the Cascadia subduction zone. Unusually large water waves could cause damage to docks and ships, coastal inundation, erosion of coastal areas, damage to shoreline structures, and triggering of landslides on eroding bluffs. Such damage has occurred in past earthquakes in other areas (e.g., Korgen, 1995; Ruscher, 1999). The 1959 M7.1 Hebgen Lake, Montana, earthquake was responsible for damage to the Hebgen dam when a seiche caused water to overtop the dam several times.
We follow a variety of modelling approaches to explain what happened in Lake Union in November of 2002. This involves the solution of shallow-water equations using finite elements and finite differences. The final goal of this work is the prediction of water wave amplitudes during large local and regional seismic events.
Everyone welcome!