Abstract
In the morning of September 27, 1611, a strong earthquake hit the Aizu Basin and its surroundings. The damage and its location are thoroughly described in old documents. Landslides occurred in many places on the upthrown side of the Aizu active fault system, which borders the western fringe of the basin. The earthquake fault occurred along the active fault system and dammed up the Nippashi (Ohkawa) River, forming a small lake. The altitude of the lake is inferred to have been 174.5-175m above sea level and depth about 2-3m. The lake is assumed to have been 2-2.5km wide and 4km long, which coincides with the description of old documents. Some villages were submerged and moved outside of the lake. Some part of the ancient Echigo Highway was also submerged and were rebuilt about 4km southward. The earthquake is believed to be caused by the Aizu active fault system. The magnitude of the earthquake is calculated at about M7.3, based on the vertical displacement (2.5m) of the earthquake fault.
