HR: 1340h
AN: S13C-1453    [Abstracts]
TI: Limitation of the Predominant-Period Estimator for Earthquake Early Warning and the Initial Rupture of Earthquakes
AU: * Yamada, T
EM: takuji@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033, Japan
AU: Ide, S
EM: ide@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033, Japan
AB: Earthquake early warning is an important and challenging issue for the reduction of the seismic damage, especially for the mitigation of human suffering. One of the most important problems in earthquake early warning systems is how immediately we can estimate the final size of an earthquake after we observe the ground motion. It is relevant to the problem whether the initial rupture of an earthquake has some information associated with its final size. Nakamura (1988) developed the Urgent Earthquake Detection and Alarm System (UrEDAS). It calculates the predominant period of the P wave (τ_p) and estimates the magnitude of an earthquake immediately after the P wave arrival from the value of τ_p^max, or the maximum value of τ_p. The similar approach has been adapted by other earthquake alarm systems (e.g., Allen and Kanamori (2003)). To investigate the characteristic of the parameter τ_p and the effect of the length of the time window (TW) in the τ_p^max calculation, we analyze the high-frequency recordings of earthquakes at very close distances in the Mponeng mine in South Africa. We find that values of τ_p^max have upper and lower limits. For larger earthquakes whose source durations are longer than TW, the values of τ_p^max have an upper limit which depends on TW. On the other hand, the values for smaller earthquakes have a lower limit which is proportional to the sampling interval. For intermediate earthquakes, the values of τ_p^max are close to their typical source durations. These two limits and the slope for intermediate earthquakes yield an artificial final size dependence of τ_p^max in a wide size range. The parameter τ_p^max is useful for detecting large earthquakes and broadcasting earthquake early warnings. However, its dependence on the final size of earthquakes does not suggest that the earthquake rupture is deterministic. This is because τ_p^max does not always have a direct relation to the physical quantities of an earthquake.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7209 Earthquake dynamics (1242)
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: 2007 Fall Meeting