HR: 15:20h
AN: S23E-06    [Abstracts]
TI: Seismic Intensity Magnitude for Earthquake Early Warning
AU: * Yamamoto, S
EM: syama@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1, Tennodai Ibaraki, Tsukuba, 305-0006, Japan
AU: Horiuchi, S
EM: horiuchi@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1, Tennodai Ibaraki, Tsukuba, 305-0006, Japan
AU: Nakamura, H
EM: manta@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1, Tennodai Ibaraki, Tsukuba, 305-0006, Japan
AU: Wu, C
EM: wu@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1, Tennodai Ibaraki, Tsukuba, 305-0006, Japan
AU: Rydelek, P
EM: par@ceri.memphis.edu
AF: National Research Institute for Earth Science and Disaster Prevention, 3-1, Tennodai Ibaraki, Tsukuba, 305-0006, Japan
AB: A reliable prediction of the shaking intensity from s-waves is the primary purpose of any earthquake early warning (EEW) system. To date, empirical regression formulae have been used to estimate this intensity from conventional seismic magnitude (e.g.,Mjma), which is the only parameter regarding earthquake size currently broadcast by an EEW. Others have claimed that the magnitude of large earthquakes can be estimated from just a couple of seconds of p-wave data, thus signifying a deterministic earthquake process; results from analysis of data from the Japanese Hi-net, Kik-net and K-NET arrays, however, do not support these claims. Here, we introduce a new parameter, seismic intensity magnitude MI, which is defined directly from observed seismic intensity Ip: MI = Ip/2 + log(r) + a*t + b - c, where r is the hypocentral distance, a = pi*f/(ln(10)*Q), and t, f, and Q are the travel time, predominant frequency and Q for the p-waves, b is a constant and c is a site correction term. The intensity Ip is determined from three- component seismograms of the p-wave in which the filtered signal exceeds a given level for a certain amount of time after the p-arrival. We are able to determine MI in real-time and can therefore estimate the seismic intensity for s-waves (Is) at any site by using a pre-established relation between Is and Ip, and allowing for distance, s- wave travel times and Qs structure. To investigate effectiveness, we determined MI for 127 earthquakes recorded by Hi-net, and estimated the s-wave intensity at Hi-net sites for 11242 cases. A comparison of the observed versus predicted seismic intensity at each site reveals that the estimation error, on average, when using MI is 22% smaller than the error from an empirical method using Mjma. Most important for an EEW system, we find that MI can estimate shaking intensity more rapidly than conventional methods for larger earthquakes, which makes it a very valuable and reliable parameter in an EEW system.
UR: http://www.bosai.go.jp/e/index.html
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7294 Seismic instruments and networks (0935, 3025)
SC: Seismology [S]
MN: 2007 Fall Meeting