HR: 14:55h
AN: S13E-06    [Abstracts]
TI: Earthquake Magnitude Estimation Prior to Rupture Termination
AU: * Olson, E L
EM: olson@geology.wisc.edu
AF: University of Wisconsin Madison Geology and Geophysics Department, 1215 W Dayton St., Madison, WI 53705 United States
AU: Allen, R M
EM: rallen@geology.wisc.edu
AF: University of Wisconsin Madison Geology and Geophysics Department, 1215 W Dayton St., Madison, WI 53705 United States
AB: An estimate of earthquake moment magnitude is possible within 5 seconds of earthquake initiation for events of every magnitude, including those events which rupture for several 10's of seconds. The magnitude estimate is calculated based on the empirical relationship between the predominant period of the P-wave and moment magnitude. The predominant period is calculated from the frequency content of the data on a moving average basis for the first five seconds after the trigger. The empirically observed relationship is based upon a data set consisting of more than one hundred events with moment magnitude 3.5 - 8.3, thirty events have a moment magnitude of 6.0 or greater. The magnitude estimates for several well known large magnitude events, including Chi Chi (Taiwan, 1999), Hokkaido (Japan, 2003) and Denali (Alaska, 2002), are all calculated within 5 seconds of the P-wave trigger. These events lasted for tens of seconds and the fault rupture extended 10's - 100's of kilometers, yet in each case, the magnitude can be calculated long before the rupture has propagated over the entire surface of the faults. Additionally, for large magnitude events, such as the Chi Chi earthquake mentioned above, less than 5% of the seismic moment is released within the 5 seconds required to measure the predominant period.
DE: 7223 Seismic hazard assessment and prediction
DE: 7299 General or miscellaneous
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting