Coherency characteristics of body waves traveling in a sedimentary layer-basement system in the Kanto region, Japan

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 omega(-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.