HR: 1340h
AN: S53A-1037    [Abstracts]
TI: Far-field tsunami amplitude estimations from numerical simulations and empirical laws
AU: Reymond, D
EM: reymond.d@labogeo.pf
AF: Laboratoire de Geophysique, CEA, Boite Postale 640, F-98713 Papeete, Tahiti, French Polynesia
AU: * Okal, E A
EM: emile@earth.northwestern.edu
AF: Northwestern, University, Evanston, IL 60208, United States
AU: Hebert, H
EM: helene.hebert@cea.fr
AF: LDG, CEA-DASE, Boite Postale 12, 91680 Bruyeres-le, Chatel, France
AU: Loevenbruck, A
EM: loevenbr@dase.bruyeres.cea.fr
AF: LDG, CEA-DASE, Boite Postale 12, 91680 Bruyeres-le, Chatel, France
AB: Tsunami amplitudes in the far field can be simply estimated from the seismic moment M sub 0 of the source event, which primarily controls tsunami excitation [Talandier and Okal, 1989]. This formula used only a distance correction (1) combining geometrical spreading on the spherical Earth with a mild amount of dispersion. In the context of tsunami warning in French Polynesia, this relation has been in operational use for close to 20 years, using data in several harbors: Papeete (Tahiti), Taiohae (Marquesas) and Rikitea (Gambier Island). However, it is possible to refine it by considering the influence of additional parameters of the source, such as focal depth, source directivity, focusing effect and site amplification. In the present study, tsunamis due to 10 large earthquakes (1946 Aleutian, 1964 Alaska, 1960 and 1995 Chile, 2006 Tonga, etc. plus 3 virtual generic events) have been modeled for 57 virtual sensors distributed in the deep sea throughout the Pacific Basin and its boundaries. Computed amplitudes are compared with the values predicted by the 1989 formula, in order to discuss: (2) the constant of proportionality between tsunami amplitude and seismic moment; and (3) the possibility of defining an empirical correction for source directivity, expressed as a function of receiver azimuth relative to fault strike. Furthermore, tsunami amplitudes recorded in Papeete harbour and Nuku Hiva bay, have been compared to our numerical simulations, in order to define: (4) a constant of site amplification; and (5) a focusing constant, depending on source-receiver geometry, and expressing refraction due to variable bathymetry. The influence of focal depth is also examined. The final formula obtained, integrates the above five terms.
DE: 4564 Tsunamis and storm surges
SC: Seismology [S]
MN: 2007 Fall Meeting