Ground Motion Prediction of Subduction Earthquakes using the Ambient Seismic Field: Focus on the Nankai and Sagami Troughs in Japan

The ever-increasing construction of large-scale structures such as high-rise buildings, oil tanks, and suspension bridges requires an accurate prediction of long-period ground motions (? 4 s) to assess the seismic hazard. It has been shown in previous studies that surface-to-surface impulse response functions canbe extracted from the ambient seismic field recorded by two stations and used to predict the long-period ground motions generated by moderate crustal earthquakes in California and Japan. In this study, we first focus on the northern part of the Nankai trough where two submarine cables have been deployed by the Japan Meteorological Agency (JMA). We extracted the impulse response functions between OBSs (virtual sources) and on-land stations (receivers) and show that these offshore-onshore impulse response functions predict accurately the ground motions of moderate subduction earthquakes. Then, we focus on the Sagami trough which is located close to the Tokyo city. We extracted the impulse response functions between stations located atop the 1923 Kanto earthquake fault plane (virtual sources) and the Hi-net and MeSO-net stations located in the Kanto basin (receivers). We confirm that impulse response functions are in good agreement with the waveforms of shallow Mw ~5 earthquakes that occurred close to the virtual sources in a period range of 4 to 10 s. Finally, we extend this point source method, suitable for moderate events, to finite rupture scenarios to simulate the ground motions that could be generated by large magnitude earthquakes (Mw 6-8).