Advanced prediction of long period ground motion in Osaka during huge subduction earthquakes

There is high possibility of the occurrence of the Tonankai and Nankai earthquakes which are capable of causing immense damage to mega-city Osaka which located inside the Osaka basin.In this study，we tried to advance the long period ground motion prediction through the verification of the source modeling based on the recipe for the ground motion prediction，estimation of propagation path effect。We showed the validation of the source modeling due to the recipe from application to the actual earthquakes(2003Tokachi-oki earthquake and 2005 Miyagiken-oki earthquake).Furthermore，from theoretical long period ground motion simulation of the recordings，we proposed Q=f·Vs/2as the optimum Q value in waveform simulations using3-D Finite Difference Method。Finally，we carried out long period ground motion prediction in mega-city Osaka using the 3-D finite difference method for the expected Tonankai and Nankai earthquakes.The characteristics of the predicted long-period ground motions are related with the source location and the thicknesses of the sediments of the basin。The predominant period of ground motions is4to6second in the thick sediment area，3to4second in the thin sediment area(Basin Edge)。The durations of long period ground motions in the central part of the Osaka city are more than4minutes，and the predominant period is around 6second.These results suggest that we need to investigate the seismic safety of high-rise buildings and base-isolated buildings and so on.

There is high possibility of the occurrence of the Tonankai and Nankai earthquakes which are capable of causing immense damage to mega-city Osaka which located inside the Osaka basin. In this study, we tried to advance the long period ground motion prediction through the verification of the source modeling based on the recipe for the ground motion prediction, estimation of propagation path effect. We showed the validation of the source modeling due to the recipe from application to the actual earthquakes (2003 Tokachi-oki earthquake and 2005 Miyagiken-oki earthquake). Furthermore, from theoretical long period ground motion simulation of the recordings, we proposed Q=f・Vs/2 as the optimum Q value in waveform simulations using 3-D Finite Difference Method. Finally, we carried out long period ground motion prediction in mega-city Osaka using the 3-D finite difference method for the expected Tonankai and Nankai earthquakes. The characteristics of the predicted long-period ground motions are related with the source location and the thicknesses of the sediments of the basin. The predominant period of ground motions is 4 to 6 second in the thick sediment area, 3 to 4 second in the thin sediment area (basin edge). The durations of long period ground motions in the central part of the Osaka city are more than 4 minutes, and the predominant period is around 6 second. These results suggest that we need to investigate the seismic safety of high-rise buildings and base-isolated buildings and so on.