HR: 10:20h
AN: S12A-01    [Abstracts]
TI: Ground Motion Characteristics Considering Magnitude Dependency and Difference Between Surface and Subsurface Rupture Earthquakes
AU: * Kagawa, T
EM: kagawa@geor.or.jp
AF: Geo-Research Institute, 4-3-2, Itachibori, Nishi-ku, Osaka, 550-0012 Japan
AU: Irikura, K
EM: KojiroI@aol.com
AF: Aichi Institute of Technology, 1247, Yachigusa, Yakusacho, Toyota, 470-0392 Japan
AU: Some, P G
EM: Paul_Somerville@urscorp.com
AF: URS Corporation, 566 El Dorado Street, Pasadena, CA 91101-2560 United States
AU: Miyake, H
EM: hiroe@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sato, T
EM: satom@ohsaki.co.jp
AF: Ohsaki Research Institute, 2-2-2, Uchisaiwaicho, Chiyoda-ku, Tokyo, 100-0011 Japan
AU: Dan, K
EM: dan@ohsaki.co.jp
AF: Ohsaki Research Institute, 2-2-2, Uchisaiwaicho, Chiyoda-ku, Tokyo, 100-0011 Japan
AU: Matsu, S
EM: matu@ohsaki.co.jp
AF: Ohsaki Research Institute, 2-2-2, Uchisaiwaicho, Chiyoda-ku, Tokyo, 100-0011 Japan
AB: We have studied differences in ground motion according to fault rupture types and magnitude. We found that three diffferent earthquake categories have distinct ground motion characteristics. Somerville (2003) and Kagawa et al. (2004) found that the ground motion caused by subsurface rupture in the period range around one second is larger than predicted by empirical spectral attenuation relations (Abrahamson and Silva, 1997) for all earthquakes, but ground motion from earthquakes that rupture the surface is smaller in the same period range. We expand their study to smaller earthquakes and add several recent earthquakes. WWe began by dividing the earthquakes into four categories that are a combination of two classifications, i.e. defined and undefined fault, surface and subsurface rupture earthquakes. Each category is divided into larger and smaller earthquakes than about Mw 6.5. Eventually, we classified the earthquakes into three groups: a) Surface rupture type : Ground motion is smaller than average, especially in the period range around 1 second. b) Larger subsurface rupture type : Ground motion is larger than average, especially in the period range around 1 second. c) Smaller subsurface rupture type : Ground motion is larger than average, especially in the period range around 0.1 second. Subsurface rupture earthquakes with small magnitude occur in the deep portion of the seismogenic zone. Deep and high stress asperities generate large ground motions in the short period range. They do not generate pulse like ground motions, because the asperity is too small and deep to cause forward directivity effects, and because the radiation and propagation of ground motion at short periods may be too incoherent to allow the formation of a pulse. Larger subsurface rupture earthquakes have larger asperities that may span a large part of the width of the seismogenic zone, producing coherent directivity pulses with periods of 1 second or more. Kagawa et al. (2004) pointed out that the shallow asperities of surface rupture earthquakes have small stress drop and long rupture duration. According to present procedures of strong ground motion evaluation, large earthquakes with surface rupture (type a) are considered to be a 'characteristic earthquakes'. However, there may be cases where a 'non-characteristic earthquake'generates larger ground motion than a 'characteristic earthquake'. Therefore, we need to develop fault rupture scenarios for 'non-characteristic earthquakes' (types b and c) to estimate ground motions that are potentially more damaging than those of the 'characteristic earthquake' (type a). This requires developing several scenarios of small and large subsurface rupture earthquakes with different magnitudes within the seismogenic zone. ACKNOWLEDGEMENT: A portion of this study was supported by the JNES research topic 'Strong Ground Motion Evaluation Based on Dynamic Source Modeling' (Leader: Kojiro Irikura). REFERENCES: Abrahamson and Silva (1997), SRL, 68. Kagawa et al.(2004), EPS, 56. Somerville (2003), PEPI, 137.
DE: 7209 Earthquake dynamics (1242)
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: Fall Meeting 2005