CHARACTERISTICS OF THE RESPONSE OF THE FRACTURED ZONE AT YAMASAKI FAULT FOR TELESEISMIC SURFACE WAVES

Abstract

Some components of extensometers in the Yasutomi Observation Tunnel at Yamasaki Faultcross the fractured zones. From the analysis of continuous records of them, it was shown that thetidal strain across fractured zone is larger than that on the neighboring unfractured zone.In this paper, we have analyzed data of same extensometers and found out some character-istics of the fractured zone on the strain seismograms of teleseismic surface waves.The strain variation generated by teleseismic surface waves across the fractured zone is alsolarger than that on the unfractured zone, and the effect of amplification on long period surfacewaves is more notable than that on earthtide.We have calculated the strain seismograms at Yamasaki Fault from the displacement seismo-grams at the Abuyama Seismological Observatory and compared them with observed ones atYamasaki Fault. The amplitude of observed ones on unfractured zone is larger than that of calculat-ed ones. These results suggest that the existence of the fractured zone gives some significant effectson the strain field in the comparatively wide region.Some components of extensometers in the Yasutomi Observation Tunnel at Yamasaki Faultcross the fractured zones. From the analysis of continuous records of them, it was shown that thetidal strain across fractured zone is larger than that on the neighboring unfractured zone.In this paper, we have analyzed data of same extensometers and found out some character-istics of the fractured zone on the strain seismograms of teleseismic surface waves.The strain variation generated by teleseismic surface waves across the fractured zone is alsolarger than that on the unfractured zone, and the effect of amplification on long period surfacewaves is more notable than that on earthtide.We have calculated the strain seismograms at Yamasaki Fault from the displacement seismo-grams at the Abuyama Seismological Observatory and compared them with observed ones atYamasaki Fault. The amplitude of observed ones on unfractured zone is larger than that of calculat-ed ones. These results suggest that the existence of the fractured zone gives some significant effectson the strain field in the comparatively wide region