Abstract
Kamegawa fault locates at the western part of Beppu Bay Graben. Based on the trenching study of the fault, we obtained some new evidences on the activity of Kamegawa fault. The fault plane in trench 1 shows the strike of N86°W and dip of 75°-85°S. Tephra and gravel layers are deformed along the fault plane by faulting.
The faulting of Kamegawa fault is estimated to have occurred at three times since the deposition of AT(Aira Tn) volcanic ash (23,000 years BP). The latest faulting is considered to have occurred during 2,020∼3,400 years BP, before accumulation of the Yufudake volcanic ash. The reccurence interval is about several thousands of years with 60∼80 cm vertical slip.
