We examine the construction methodology of a source model for strong ground-motion prediction of scenario earthquakes with a long active-fault zone including a multi-segment rupture case. For the multi-segment rupture event, different seismic moments are given by applying two different source-model construction methodologies: (1) a methodology based on seismological scaling relationships and (2) a methodology in an active-fault study based on the cascade model (Working Group on California Earthquake Probabilities, 1995). The difference between these methodologies is whether or not a slip of each segment depends on total rupture length. We investigate which construction methodology is more appropriate for the construction of the source model. We use the two methodologies to construct characterized source models for strong ground-motion simulations of the 1891 Nobi earthquake, which was a multi-segment rupture event occurring in the Nobi active-fault system. We evaluate the constructed source models by comparing the seismic intensities obtained from simulated waveforms with those estimated from the questionnaire-based intensities determined by Muramatu and Kominami (1992). The characterized source model constrained by seismological scaling relationships can give a more adequate distribution of the estimated seismic intensities. We also suggest that the Gifu-Ichinomiya fault might be considered as a source fault to explain the damage distribution on the Nobi Plain.

To investigate possible source fault models for the Gifu-Ichinomiya fault, we construct multiple source fault models of the 1891 Nobi earthquake, taking into account several different types of geometry for the GifuIchinomiya fault, and conduct strong ground motion simulations. We choose the most plausible source model by comparing the distribution of simulated seismic intensities with the spatial distribution of a questionnairebased intensity of 7, and with that of the damage ratio of wooden houses in the near-source region. Our results imply that the length of the source fault of the Gifu-Ichinomiya fault is relatively short and the dip angle is 75 degrees to the east. Because a seismic intensity of 7 is considered to arise from site amplification and the short distance from a source fault, we classified the points with a seismic intensity of 7 based on the H/V spectral ratio of microtremors by considering the contributing factors to the generation of a seismic intensity of 7. A linear distribution of the points, which might have relatively lower site amplification factors, in the northeastern part of the Nobi Plain implies that a part of the source fault of the 1891 Nobi earthquake existed in this area, as indicated through strong ground motion simulations.

During the 2007 Noto Hanto earthquake, a K-NET station ISK005, which is located in Anamizu town and approximately 19 km far from the epicenter, recorded the ground velocity larger than 100 cm/s. A set of observational study is carried out to investigate spatial variation of ground motion amplification characteristics in Anamizu town. Firstly, the spatial variation of the amplification was observed by aftershock observations along a temporary linear seismic array across Anamizu town. In the center of the town, the spectral amplification factor is 10 to 20 between 1 Hz and 2 Hz with respect to the rock site. Then, dense single-station microtremor observations were carried out at 147 sites with average spacing of 100 m in Anamizu town to see the spatial variation in thickness of low-velocity layers. The peak frequency of the microtremor H/V spectral ratio varies from 0.8 to 2.0 Hz in the town. The velocity structure model of shallow portion in Anamizu town is estimated from the mircrotremor H/V spectral ratios. The thickness of low-velocity layers (V Sῑ70 to 100 m/s) changes along the Omata and the Manai rivers. Finally, a three-dimensional ground motion simulation is conducted using the obtained velocity structure model in order to see relationship between shallow sedimentary layers and ground motion amplification in Anamizu town. The peak velocity in the frequency range below 2.5 Hz is three or four times larger in the area around ISK005, where the thickness of low-velocity layers is approximately 10 to 25 m, than that in the rock side. It could be concluded that the ground motion amplification characteristics in the frequency range between 1 Hz and 2 Hz is mainly controlled by the existence of such low-velocity sedimentary layers.

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