HR: 1340h
AN: S13A-1038    [Abstracts]
TI: A probabilistic estimation of magnitude in a real-time warning system using a magnitude-frequency distribution
AU: * Iwata, T
EM: iwata@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenno-dai, Tsukuba, 305-0006 Japan
AU: Imoto, M
EM: imoto@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenno-dai, Tsukuba, 305-0006 Japan
AU: Horiuchi, S
EM: horiuchi@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenno-dai, Tsukuba, 305-0006 Japan
AB: In a real-time warning system, it is important to estimate quickly the magnitude of an earthquake. Here, for this quick estimation, we suggest a probabilistic estimation using the magnitude-frequency distribution of earthquakes. It is ideal that the magnitude can be estimated using the first few seconds of wave data for the quick estimation. However, there is a possibility that the magnitude, which is estimated quickly, for large earthquakes is underestimated. An earthquake with a magnitude of about 8 (M8 class earthquake) has a source duration of a few tens of seconds. Thus, only using the first few seconds of wave data, the estimation of the magnitude is carried out before the stop of the earthquake rupture. As the wave data include incomplete information of the rupture process, the magnitude estimated quickly would be underestimated. Therefore, when we detect an occurrence of an earthquake with a magnitude of 6 or 7 in a region where an M8 class earthquake is expected, we need to determine whether or not the rupture of the earthquake grows and its magnitude finally reaches 8. For this determination, a probabilistic estimation using the magnitude-frequency distribution (e.g., the Gutenberg-Richter relation) is suggested. In case when we detect an occurrence of an earthquake in a focused region, we estimate the magnitude of this earthquake quickly. Then, we calculate the probability that the magnitude of this earthquake finally exceeds a certain magnitude using the derived magnitude-frequency distribution, the Bayesian inference, and the estimated magnitude. For example, in Tokai region, central Japan, where an M8 class earthquake is expected, the magnitude-frequency distribution follows the Gutenberg-Richter relation in the magnitude range less than 6, but the relation breaks for the large magnitude range. Thus, in case when we detect an occurrence of an earthquake of which magnitude is larger than 6, there is high possibility that its magnitude would reach 8 finally.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7294 Instruments and techniques
DE: 7215 Earthquake parameters
DE: 1734 Seismology
SC: Seismology [S]
MN: 2004 AGU Fall Meeting