The Niinuma landslide area has been in motion since the Niigata Earthquake (June 16th 1964), and its latest activity gradually set in motion during a spell of rainy days before the Tokachi-oki Earthquake. (The hamlet of Niinuma is situated on the gentle slope formed by a past lanbslide in the hill-land area west of the Nagai Basin.) The Tokachi-oki Earthquake dccurred on May 16th, 1968 on the Pacific side of Aomori Pref. In the Niinuma area about 430 km from its epicenter, there occurred fissures, landslides and depressions on the paddy fields right after this earthquake and its aftershock.