(4)Earthquakes in the southern Hidaka Mountains
In the Pacific Ocean off the southern part of the Hidaka Mountains, the trench bends from a roughly north-south direction (Japan Trench) to a northeast-southwest direction (Chishima Trench). This bend in the trench also causes a bend in the subducting Pacific Plate, and the subterranean area is thought to be greatly distorted. In the Chishima Trench, the Pacific Plate is subducting obliquely, dragging the earth's crust on land in a westward direction. This earth's crust is thought to be colliding with the earth's crust in the southwestern part of Hokkaido in the southern part of the Hidaka Mountains. Thus, a great deal of strain has built up from the southern Hidaka Mountains to the area off the coast of Urakawa due to the large distortion and unique underground structure caused by the bend in the plate, as well as to the collision with the earth's crust resulting from the obliquely subducting plate. As a result the seismic activity in this area is quite active. Several large earthquakes have occurred here, including the 1982 Earthquake off the Coast of Urakawa (M 7.1) and the 1970 earthquake in the Hidaka Mountains (M 6.7). These earthquakes occurred at somewhat deeper locations (20-40 km) than those that normally occur on land (depths of 20 km or less). Therefore, the damage tends to be alleviated somewhat. In addition, many earthquakes occur in deeper areas that are directly related to the subducting of the Pacific Plate.