Seismic wave simulation at DONET ocean-bottom stations

Abstract

We deployed a dense seismic and tsunami array, namely DONET (Dense Oceanfloor Network System for Earthquakes and Tsunamis), in water depths of 1900–4400 m near the Nankai trough in southwest Japan. We have observed broadband signals for seismic and tsunami events since the start of our operation in 2010. In this study, we attempt to reproduce seismic waveforms at DONET stations for a local event occurred in the Kii peninsula. We employ our Heterogeneity, Oceanic layer, and Topography scheme (HOT)-FDM, presented by Nakamura et al. (2012), which can implement irregular fluid-solid boundary correctly in seafloor and land surface (freesurface). The synthetic waveforms agree with observations in terms of the waveform as a whole at both of land stations (K-net) and DONET stations, demonstrating that the simulation with our HOT-FDM scheme using three-dimensional subsurface structure models is an appropriate approach for the reproduction of wavefields in land and ocean areas. We find that the peak amplitudes at DONET are larger than those at Knet stations from both of the observed and simulated results. These amplifications are significantly associated with the presence of sediment layers around the trench zone. Analyzing DONET data and their simulations contribute to developing our understandings of seismic wavefields in ocean area where subduction events have repeatedly occurred.