Evaluation of Power Spectrum Intensity With Very High Density in Residential Valley-Filling Area During a Future Large-Scale Earthquake

Abstract eng:
The 2011 off the Pacific coast of Tohoku, Japan, earthquake caused significant damage, not only due to tsunamis but also due to strong motions. The damage to housing may be classified into tsunami-related damage, damage due to ground liquefaction on newly reclaimed land, and that caused by the instability of slope sand fill embankments developed for residential use. Nowadays, many approaches which simulate the slope failure based on numerical analysis are carried out. On the other hand, it is very important to predict and evaluate the seismic response characteristics of residential valleyfilling area during a future large-scale earthquake based on the obtained moderate earthquake observation record. Regarding this indication, we have already focused on the damaged one to housing lots on hillside embankments. Emphasis is placed on the damage and failure of the housing lots on the hillside embankments in Sendai City, a city with a population in excess of one million, making it one of the largest cities in East Japan. We have then succeeded in clarifying the landslide mechanism of the residential fill slopes due to the 2011 off the Pacific coast of Tohoku Earthquake. It is important to use efficiently the obtained findings in the prediction and evaluation of damage and failure of a residential fill embankment during a future large-scale earthquake. At present, in Japan, event probability of a large-scale earthquake whose epicenter has Tokyo Metropolitan Area is increasing. Yokohama City, a city with a population in excess of three million, located in the metropolitan area has the greatest residential land in Japan. A large part of the residential land consists of cutting or banking site of valley-filling. Due to the 1978 off Miyagi Prefecture Earthquake, the 1995 Southern Hyogo Prefecture Earthquake, the 2004 Mid Niigata Prefecture Earthquake and the 2011 off the Pacific coast of Tohoku Earthquake, serious damage are reported at the banking site of valley-filling in Sendai City, Kobe City and so on. Thus, during the future Tokyo Metropolitan Earthquake represented by the Northern Tokyo Bay Earthquake by Japanese Cabinet Office, the similar damage at a banking site of valley-filling in Yokohama City can imagine without difficulty. In this paper, seismic response characteristics of the residential land in Yokohama City are evaluated based on temporary earthquake observation records. In particular, first, a lot of seismograph installed with very high dense spatial location at not only cutting but also banking sites of residential valley-filling in Kanagawa Ward, Yokohama City, Japan. Seismic waveform records are then obtained simultaneously at the created observation station sites during some moderate earth-quakes. Based on the analysis consequence of the observed seismic waveforms, furthermore, difference of the seismic response characteristics between the cutting sites and the banking sites was evaluated. Finally, ground motion estimation was carried out during the Northern Tokyo Bay Earthquake based on the evaluated local site effects. At that time, as an index of ground motion, we took into consideration the velocity power spectrum intensity (PSI) value with strong relation with the past seismic damage of residential fill embankment. Our related discussion and obtained findings will be useful in future evaluation of seismic performance of a residential fill embankment.

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