[S07-5] Simulation for scenario earthquakes and strong motion monitoring / processing

[S07-5-01] Simulation of Strong Ground Motions in and around Iwaki City, Fukushima Prefecture, using Pseudo Point-source Model

^○Takumi Hayashida¹, Toshiaki Yokoi¹, Hiroto Nakagawa¹, Toshihide Kashima¹, Shin Koyama² (1.Building Research Institute, Tsukuba, Ibaraki, Japan, 2.National Institute for Land and Infrastructure Management, Tsukuba, Ibaraki, Japan)

After the 2011 Mw9.0 Tohoku earthquake, a great number of aftershocks occur near the source region off the Pacific coast of eastern Honshu. We deployed a dense temporary seismic array consisting of 16 stations in Iwaki city, Fukushima prefecture from November 2014 to September 2015. During the observation period, at least 100 felt earthquakes (Mw in the range of 3.5-7.9) including 75 intraslab and interplate earthquakes along the subduction zone were detected. Previously we applied spectral inversion method to the event data and estimated site amplification factors at each station as well as seismic quality factor (Hayashida et al., 2017). In this study we performed spectral inversion method again by adding event data from K-NET (six stations) and KiK-net (three stations) of National Research Institute for Earth Science and Disaster Resilience (NIED) in and around Iwaki city, and strong motion data of Building Research Institute (BRI) recorded at basement floor of Iwaki city hall, during the same observation period. To perform the inversion, several constraints (rock site assumption, proposed site amplification model, proposed attenuation model or source spectra for selected aftershocks) were employed and we found that the inversion with proposed site amplification model (at K-NET FKS011 station) provides reasonable results. Next we simulated strong ground motions with the pseudo point-source model (Nozu, 2012) using modeled source spectra, the estimated quality factor and site amplification factors for the mainshock of the 2011 Tohoku earthquake and the 2016 Fukushima earthquake (November 22, Mw7.0). The seismic source spectra are modeled using the omega-square model from available source models with phase characteristics of the selected subevents (point source) from our dataset. The synthetic waveforms and its Fourier spectra of S-wave portions show reasonable agreements with observed ones in the frequency range between 0.2 and 10 Hz.