Edge wave and non-trapped modes of the 25 april 1992 Cape Mendocino tsunami |
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| Authors: | F I González K Satake E F Boss H O Mofjeld |
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| Institution: | (1) Pacific Marine Environmental Laboratory/NOAA, 7600 Sand Point Way NE, 98115 Seattle, WA, USA;(2) Dept. Geological Sciences, University of Michigan, 1006 CC Little Bldg., 48109 Ann Arbor, MI, USA;(3) Joint Institute for Study of Atmosphere and Ocean, University of Washington, 98195 Seattle, WA, USA |
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| Abstract: | The 25 April 1992 Cape Mendocino earthquake generated a tsunami characterized by both coastal trapped edge wave and non-trapped tsunami modes that propagated north and south along the U.S. West Coast. Both observed and synthetic time series at Crescent City and North Spit are consistent with the zero-order edge wave mode solution for a semi-infinite sloping beach depth profile. Wave amplitudes at Crescent City were about twice that observed at North Spit, in spite of the fact that the source region was three times farther from Crescent City than North Spit. The largest observed amplitude was due to an edge wave which arrived almost three hours after the initial onset of the tsunami; since such waves are highly localized nearshore, this suggests that the enhanced responsiveness at Crescent City is at least partly due to local dynamic processes. Furthermore, the substantially delayed arrival of this wave, which was generated at the southern end of the Cascadia Subduction Zone, has significant implications for hazard mitigation efforts along the entire U.S. West Coast. Specifically, this study demonstrates that slow-moving but very energetic edge wave modes could be generated by future large tsunamigenic earthquakes in the CSZ, and that these might arrive unexpectedly at coastal communities several hours after the initial tsunami waves have subsided. |
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| Keywords: | Tsunamic edge waves Cape Mendocino Cascadia Subduction Zone hazard mitigation |
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