Abstract
After the 2011 Tohoku earthquake, the shallow earthquakes increased in off Ibaraki and Fukushima prefecture area, Japan. We examined the long-period strong ground motion in the Tokyo bay area from those events with hypocenter depth shallower than 60 km and magnitude over 6.5 in Japan Meteorological Agency scale. The duration of the velocity waveform of shallower event was longer than that from deeper event and the amplitude of the long-period ground motion of shallower event was larger than that of deeper event. The later arrivals with period of 3-10 second affected these phenomena. There was the case that source mechanism affected on the excitation of long-period strong ground motion. Consideration of source depth and source mechanism is necessary to evaluation of the long-period ground motion in the Tokyo Bay area. In addition, the site amplification of body waves was also observed in long-period range. It is important to evaluate the site effect of deep sub-surface structure.
