Abstract

By means of borehole array recordings obtained at six stations from local events, we estimated coherency characteristics of body waves that propagate in a sedimentary layer–basement system in the Kanto region, Japan. The estimated coherence is characterized by an ω−2 model for P and S waves. An important result is that the values of corner frequency become nearly constant, 5–6 Hz, in travel times less than 2.5 sec for SH waves. This suggests that bedrock motions recorded in the pre-Tertiary basement are becoming incoherent in high frequencies. Also, the corner frequency of P waves is approximately twice that for SH waves. Hence, P waves propagate coherently in high frequencies as compared with SH waves.

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