Last Update 05/27 2014
An earthquake is a phenomenon, which begins at its source with fault motion and is completed after the propagation of seimic waves through the Earth and the excitation of ground motions and crustal deformations at a site. This laboratory works, based on the research theme: "Think Seismic Shaking Scientifically.", for various seismic shakings and deformations such as strong shaking causing disasters (strong motion) and long-period ground motion. (http://taro.eri.u-tokyo.ac.jp/saigai/kenkyuE.html for details)
1. The earthquake source greatly affects seismic waves, ground motions, and crustal deformations, so that we are studying the details of earthquake source process (e.g., Sato et al., 2005). Using the resultant models we challenge mysteries in earthquake source mechanics and crustal dynamics: what happens or what kind of shaking is generated in a source region?
2. The velocity structures of the crust, descending plates and near-surface sediments are also influential in seismic waves, ground motions, and crustal deformations. So, we have developed a new scheme of seismic ray tracing and carried out tomographic analyses (e.g., Koketsu and Higashi, 1992). However, we still need advanced velocity structure models to simulate realistic ground motions and deformations, and are seeking a breakthrough in velocity structure modeling.
3. Observations and simulations can promote researches on seismic waves, ground motions, and crustal deformations. We were participated in the development of a network of 600 stations in the Kanto basin, and investigated how the long-period ground motion propagated within the basin (Koketsu and Kikuchi, 2000). We also confirmed that a ground motion simulation in the above velocity structure model can reproduce these observations. We are seeking a way to utilize such data and a new method of the simulation.
Koketsu, K. and S. Higashi, Three-dimensional topography of the sediment/basement interface in the Tokyo metropolitan area, central Japan, Bull. Seism. Soc. Am., 82, 2328--2349, 1992.
Koketsu, K. and M. Kikuchi, Propagation of seismic ground motion in the Kanto basin, Japan, Science, 288, 5469, 1237--1239, 2000.
Sato, H., N. Hirata, K. Koketsu, D. Okaya, S. Abe, R. Kobayashi, M. Matsubara, T. Iwasaki, T. Ito, T. Ikawa, T. Kawanaka, K. Kasahara and S. Harder, Earthquake source fault beneath Tokyo, Science, 309, 5733, 462--464, 2005.
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纐纈一起, 兵庫県南部地震と強震動地震学, 科学, 70, 1, 66--71, 2000.
纐纈一起, 関東平野の地下構造調査とそのモデル化, 月刊地球, 号外, 37, 96--101, 2002.