Characteristics of Long-Period Ground Motions in the Tokyo Metropolitan Area and its Vicinity, by Recording Data of the 2011 Off the Pacific Coast of Tohoku Earthquake (Mw 9.0) and the Aftershocks

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We evaluated the characteristics of earthquake ground motions and site amplification factors for periods more than 2 seconds in the Tokyo Metropolitan Area and its vicinity, by the main shock and aftershocks of the 2011 off the Pacific coast of Tohoku Earthquake. The complex distribution of earthquake ground motions by PGV and PGA in the Tokyo Metropolitan Area were shown, using recording data of the main shock observed at seismic stations of about 650. Also, the pseudo velocity responses for periods of 2 and 3 seconds in Kawasaki to Shinagawa were extremely large. Site amplification factors, which were estimated by the ratio of velocity response spectra on surface to those in the seismic bed rock, have the azimuthal dependence to epicenter for periods more than 3 seconds. Long-period ground motions in the Tokyo Metropolitan Area were more largely amplified by earthquakes located in Northern Nagano Pref. and Eastern Shizuoka Pref. than those located in Tohoku Region.