P waves to seismological stations in Japan from the underground explosion of November 6, 1971, at Amchitka Island.

Velocity Structure Beneath the Hidaka Mountains in Hokkaido, Japan

“…In the Hidaka Mountains, gravity anomalies measured by OOKAME (1972) and Ookawa and Kasahara (personal communication, 1983) show a high contrast characterized by a sharp change in the gravity anomaly existing between the central and western zones. NAGAMUNE (1973) and AOKI and TADA (1973) showed the existence of a strong lateral heterogeneity in P-wave velocity beneath the Hidaka Mountains region using travel time anomalies from the underground nuclear explosion at Amchitka Island, the Aleutian Islands. These gravity and travel time anomalies suggest that the crust and upper mantle structure is strongly anomalous beneath the region in and around the Hidaka Mountains.…”