Earth Planets Space, Vol. 57 (No. 3), pp. 197-202, 2005LETTER
Nobuyuki Yamada and Tomotaka Iwata
Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
(Received December 9, 2004; Revised March 3, 2005; Accepted March 4, 2005)
Long-period (5-20 s) ground motion simulations in the Kinki area during the MJ 7.1 foreshock of the 2004 off the Kii peninsula earthquakes are performed. We construct a three-dimensional underground structure model that includes the source region and Osaka basin area to confirm propagation-path effects of crustal structure on long-period ground motions. Finite difference (FD) simulations by our three-dimensional underground structure model agree well with long-period observed ground motions at several rock sites in the Kinki area. We found that a sedimentary wedge structure along the Nankai trough amplifies and elongates long-period ground motions from this event. We also examine the effect of source depth for this event by comparing the observed with synthetic waveforms. These results suggest that precise modeling of the shallower parts of the underground structure, such as the sedimentary wedge, are quite important for long-period ground motion simulation of the hypothetical Nankai and Tonankai earthquakes.
Key words: Long-period ground motion simulation, foreshock of the 2004 off the Kii peninsula earthquakes, Kinki area, FDM, underground structure model.