SEISMIC BEHAVIOR OF THE TOKYO BAY AREA DURING THE 2011 OFF THE PACIFIC COAST OF TOHOKU EARTHQUAKE USING DOWNHOLE ARRAY RECORDS

Abstract

 Underground motions within a hard diluvial stratum were obtained in the March 11th 2011 Great East Japan Earthquake at a downhole in the Tokyo Bay area, which has suffered serious sand-liquefaction over its long 42km² stretch. The motions in the diluvial sand deposit are characterized by their (1) long dura-tion times with 6 to 8s components surpassing others, (2) moderate amplitude of 51.1 cm/s² in PGA, which is estimated to have resulted in moderate average strains of 8 to 9 × 10^-4 and 5 to 7 × 10^-4 over shal-low -2 to -30m and deep -30 to -77m soil deposits, respectively. The peak strain reached in the interior of soil was estimated to be about 1.3 × 10^-3.