HR: 09:15h
AN: OS21A-05    [PDF]
TI: M-TSU: Direct evaluation of an earthquake "mantle" magnitude from ocean-bottom pressure records of tsunami waves
AU: Titov, V
EM: titov@pmel.noaa.gov
AF: PMEL-NOAA, 7600 Sand Point Way NE, Seattle, WA 98115 United States
AU: * Okal, E A
EM: emile@earth.nwu.edu
AF: Northwestern Univ., Locy Hall, Evanston, IL 60208 United States
AB: We apply the concept of the mantle magnitude M sub m, developed by Okal and Talandier [1989], to tsunami records obtained by ocean-bottom pressure sensors of the DART project. Our goal is to devise an algorithm to use these tsunami waveforms on the high seas, unaffected by the later interaction of the wave with coastlines, to infer the characteristics of the parent earthquake in the ultra-low frequency band, which may be improperly rendered by seismic mantle waves. Because tsunamis constitute a branch of the spheroidal oscillations of a self-gravitating Earth, it is straightforward to apply normal mode theory in order to derive a simple variant of the M sub m algorithm, to be used with tsunamis. The source correction is predicted from the theoretical expression of normal mode excitation coefficients in the range 300-6000 seconds. The distance correction is simplified from the case of seismic waves by the elimination of the effect of anelasticity (finite Q) which becomes irrelevant in the case of tsunami waves. The locking constant, still predicted theoretically, is simply adapted to the measurement of a different physical quantity -- pressure rather than displacement, and to the choice of units. We will present examples of computation of M sub TSU from actual records at DART stations.
DE: 4564 Tsunamis and storm surges
DE: 7215 Earthquake parameters
DE: 7260 Theory and modeling
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting