Long‐period ground motion simulation of a subduction earthquake using the offshore‐onshore ambient seismic field

Large earthquakes that occur in subduction zones are likely to generate long‐period ground motions that can cause severe damage even at great distances from the epicenter. We extracted surface‐to‐surface impulse response functions from the ambient seismic field recorded by offshore ocean bottom seismometers located atop the Nankai subduction zone and onshore stations. We showed that these offshore‐onshore impulse response functions can be used to accurately simulate the long‐period ground motions generated by an offshore moderate subduction earthquake. Moreover, we also found that the distributions of the earthquake and impulse response function pseudovelocity response spectra have similar maximum amplifications in the same area close to the earthquake epicenter. This suggests that the ambient seismic field recorded by the increasing number of ocean bottom seismometers around the world can be used to assess seismic hazard related to offshore subduction earthquakes without prior knowledge of the velocity structure.