地震動尾部に現れるパルス状震動の繰り返し

概要

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The Waseda bore-hole seismometer array, Tokyo, occasionally records periodic repetition of seismic pulses in coda part of seismic waves. Each pulse looks like a Ricker wavelet of several to ten second duration and of repetition intervals for about 10-20 and 50-60 sec. Total duration of the ground motion of this type reaches 5 minites. Obervation at other stations seems to suggest that such coda pulses of our interest could be observed in a considerably wide area in and around Tokyo Metropolis. Seismological analyses of the records and numerical tests of wave propagation prove that a possible mechanism of the present pulse events is generation of local surface waves and multiple horizontal reflection of them between underground boundaries. The main reflector may be located at the outer rim of the thick sedimentary basin. Further conclusion must be made after precise location of the reflectors, using dense array newtwork data and information of local underground structures. From the engineering point of view, repetition of seismic pulses as above may affect seismic vibration of artificial structures. Large artificial structures of long period and low damping factor might undergo additional vibration by the pulses, if the characteristic periods fit the interval of the pulses.
社団法人日本建築学会の論文
1990-03-25