HR: 14:00h
AN: S43C-02    [Abstracts]
TI: Tsunami Observations on Hydrophones and Island Seismic Stations
AU: * Hanson, J A
EM: jeffrey.a.hanson@saic.com
AF: Science Applications International Corporation, 10260 Campus Point Dr., San Diego, CA 92121, United States
AU: Bowman, J R
EM: roger.bowman@saic.com
AF: Science Applications International Corporation, 10260 Campus Point Dr., San Diego, CA 92121, United States
AU: Reasoner, C L
EM: colin.l.reasoner@saic.com
AF: Science Applications International Corporation, 10260 Campus Point Dr., San Diego, CA 92121, United States
AU: Shields, G
EM: gordon.shields@saic.com
AF: Science Applications International Corporation, 10260 Campus Point Dr., San Diego, CA 92121, United States
AB: The tsunami generated by the great Indonesian earthquake of 26 December 2004 was recorded across a myriad of technologies, many of which had not been designed, nor expected, to record tsunami signals. We reported on the tsunami signals from this event observed at hydrophones, intended for nuclear test monitoring, and broadband seismometers that are part of the global seismic network (GSN). Our observations led us to examine more recently reported tsunamis and other historic tsunamis. The great Sumatra-Andaman earthquake (Mw 9.1) produced high-frequency (greater than 5 mHz) dispersed tsunami signals, in addition to the destructive wave, recorded by hydrophone stations offshore from Diego Garcia and Cape Leeuwin, Australia, and by many seismic stations in the Indian Ocean and on the coast of Antarctica. Dispersed energy was observed to 60 mHz. The details within the dispersed signal provided source information to which tide gauge data are insensitive. The source of high-frequency signals could be determined using event- to-station distances estimated from the dispersion. Fine structure in the tsunami signal indicated a possible secondary high-frequency source. The dispersion observations and modeling also identified individual reflector sources over basin-wide distances. Two other recent tsunamis were observed in the Indian Ocean. The 28 March 2005 earthquake (Mw 8.6) produced high-frequency tsunami waves (to 20 mHz) observed at the Diego Garcia hydrophone station and the AIS seismic station. In addition, the lower frequency, non-dispersed tsunami waves were seen at four other seismic stations. The Mw 7.7 earthquake on 17 July 2006 south of Java also generated high frequency tsunami waves (to 10 mHz). Clear, dispersed signals were observed on hydrophone stations and seismic stations at the Cocos-Keeling Islands, and Casey, Antarctica. The first arriving energy is consistent with a source located at the earthquake epicenter. However, the strongest signals at Cocos-Keeling and Diego Garcia islands arrive after the initial onset, indicating a secondary source area or strong reflections. Island seismic station data from the Pacific were examined for tsunami signals for 14 earthquakes in the circum- Pacific region between 1994 and 2003 with Mw 7.1 to 8.4 that were known to be tsunamigenic. The seismic signals were compared to tide gauge recordings when available. Tsunami signals from 0.5 mHz up to 2-8 mHz were observed at the expected arrival time on the horizontal components of low-elevation seismic stations near coastlines for eight of the 14 earthquakes. Lower amplitude signals were observed for the other six. Dispersed tsunami signals between 1 and 8 mHz were observed for two earthquakes (Mw 8.2-8.4) and were consistent with predictions. The observations suggest that seismic data could be used to complement tide gauges and ocean bottom pressure recorders for tsunami monitoring and research.
DE: 4259 Ocean acoustics
DE: 4564 Tsunamis and storm surges
DE: 7200 SEISMOLOGY
SC: Seismology [S]
MN: 2007 Fall Meeting