Finite-Difference Simulation of Long-Period Ground Motion for the Sagami Trough Megathrust Earthquakes
Asako Iwaki, Nobuyuki Morikawa, Takahiro Maeda,
Shin Aoi, and Hiroyuki Fujiwara
National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba, Ibaraki 305-0006, Japan
We perform long-period ground motion simulations for Sagami Trough earthquakes by a three dimensional finite-difference method. The Sagami Trough has been the site of two well-known megathrust earthquakes, the 1923 Taisho- and the 1703 Genroku-type Kanto earthquakes. However, a lack of accumulated historical earthquake records prevents us fromobtaining knowledge of the source model of the next anticipated event for long-period ground motion hazard evaluation. Therefore, it is important to consider numerous possibilities for the unknown source parameters. We compare ground motions for several scenarios with different source area, and with magnitudes ranging from Mw7.9 to 8.6. Peak ground velocity (PGV) within the Kanto basin, including the Tokyo metropolitan area, differs by several times depending on the choice of the source area. The effects of the variety in fault parameters, such as rupture starting points and asperity patterns, are also studied. They can greatly vary the ground motion within the Kanto area, especially in the direction of rupture propagation, suggesting the severe impact of directivity effects. Source models with different rupture starting points produce PGV and 5% damped velocity response (Sv) that vary from each other by as much as 10-20 times. PGV and Sv vary by up to five times depending on the asperity pattern. Our simulation results show that the predicted ground motion for the earthquake scenarios strongly depends on both the source size and other fault parameters of the source models. It is suggested that the seismic hazard assessment requires statistical evaluation of ground motions from as many source models as possible in order to overcome the uncertainties of the source.
-  K. Koketsu andM. Kikuchi, “Propagation of seismic ground motion in the Kanto basin, Japan,” Science, Vol.288, pp. 1237-1239, 2000.
-  K. Koketsu and H. Miyake, “A seismological overview of longperiod ground motion,” Journal of Seismology, Vol.12, pp. 133-143, 2008.
-  T. Usami, “Materials for comprehensive list of destructive earthquakes in Japan -2001,” University of Tokyo Press, Tokyo, Japan, 2003 (in Japanese).
-  T. Matsuda, Y. Ota, M. Ando, and N. Yonekura, “Fault mechanism and recurrence time of major earthquakes in southern Kanto district, Japan, as deduced from coastal terrace data,” Geological Society of American Bulletin, Vol.89, pp. 1610-1618, 1978.
-  Y. Namegaya, K. Satake, and M. Shishikura, “Fault models of the 1703 Genroku and 1923 Taisho Kanto earthquakes from coastal movements in the southern Kanto area,” Annual Report on Active Fault and Paleoearthquake Researches, AIST, No.11, pp. 107-120, 2011 (in Japanese with English abstract).
-  T. Sagiya, “Interplate coupling in the Kanto district, central Japan, and the Boso peninsula silent earthquakes in May 1996,” Pure and Applied Geophysics, Vol.161, pp. 2327-2342, 2004.
-  K. Shimazaki, H. Y. Kim, T. Chiba, and K. Satake, “Geological evidence of recurrent great Kanto earthquakes at the Miura Peninsula, Japan,” Journal of Geophysical Research, Vol.116, B12408, 2011.
-  Earthquake Research Committee, “Long-term evaluation of seismic activities at the Sagami Trough,” 2004 (in Japanese),
http://www.jishin.go.jp/main/chousa/04aug_sagami/index.htm [accessed July 28, 2013]
-  N. Uchida, T. Matsuzawa, J. Nakajima, and A. Hasegawa, “Subduction of a wedge-shaped Philippine Sea plate beneath Kanto, central Japan, estimated from converted waves and small repeating earthquakes,” Journal of Geophysical Research, Vol.115, B07309, 2010.
-  H. Kimura, K. Kasahara, and T. Takeda, “Subduction process of the Philippine Sea plate off the Kanto district, central Japan, as revealed by plate structure and repeating earthquakes,” Tectonophysics, Vol.472, pp. 18-27, 2009.
-  Y. Yukutake, T. Takeda, and A. Yoshida, “Detailed spatial distribution of hypocenters and focal mechanisms in the collision zone of the Izu-Bonin arc,” Bulletin of Hot Springs Research Institute of Kanagawa Prefecture, Vol.42, pp. 9-18, 2010 (in Japanese).
-  Earthquake Research Committee, “Long-period grond motion hazard map of Japan, prototype 2012,” 2012 (in Japanese), http://www.jishin.go.jp/main/chousa/12_choshuki/dat/index.htm [accessed July 28, 2013]
-  M. Matsu’ura, T. Iwasaki, Y. Suzuki, and R. Sato, “Statical and dynamical study on faulting mechanism of the 1923 Kanto earthquake,” Journal of Physics of the Earth, Vol.28, pp. 119-143, 1980.
-  D. J.Wald and P. G. Somerville, “Variable-slip rupture model of the great 1923 Kanto, Japan, earthquake: geodetic and body-waveform analysis,” Bulletin of the Seismological Society of America, Vol.85, pp. 159-177, 1995.
-  Earthquake Research Committee, “Strong motion prediction method (“Recipe”) for earthquake with specified source faults,” revised version released on Apr 11, 2008, 40pp. (in Japanese).
-  T. Maeda, N. Morikawa, A. Iwaki, S. Aoi, and H. Fujiwara, “Finite-Difference Simulation of Long-Period Ground Motion for the Nankai Trough Megathrust Earthquakes,” Journal of Disaster Research, Vol.8, No.5, 2013 (this issue).
-  J. D. Eshelby, “The determination of the elastic field of an ellipsoidal inclusion, and related problems,” Proceedings of the Royal Society, Vol.A241, pp. 376-396, 1957.
-  H. Nakamura and T. Miyatake, “An approximate expression of slip velocity time funcion for simulation of near-field strong gtound motion,” Journal of Seismological Society of Japan (Zisin 2), Vol.53, pp. 1-9, 2000 (in Japanese with English abstract).
-  S. Aoi and H. Fujiwara, “3D finite-difference method using discontinuous grids,” Bulletin of Seismological Society of America, Vol.89, pp. 918-930, 1999.
-  T. Sato, R. W. Graves, P. G. Somerville, and S. Kataoka, “Estimates of regional and local strong motions during the great 1923 Kanto, Japan, earthquake (MS 8.2). Part 2: Forward simulation of seismograms using variable-slip rupture models and estimation of near-fault long-period ground motions,” Bulletin of Seismological Society of America, Vol.88, pp. 206-226, 1998.
-  H. Sekiguchi, M. Yoshimi, H. Horikawa, K. Yoshida, S. Kunimatsu, and K. Satake, “Prediction of ground motion in the Osaka sedimentary basin associated with the hypothetical Nankai earthquake,” Journal of Seismology, Vol.12, pp. 185-195, 2008.
-  R. W. Graves and A. Pitarka, “Broadband ground-motion simulation using a hybrid approach,” Bulletin of Seismological Society of America, Vol.100, pp. 2095-2123, 2010.