The Great Kantō Earthquake was a megathrust earthquake that struck the Kantō Plain on the main Japanese island of Honshu at 11:58:32 JST on Saturday, 1 September 1923. It had an approximate magnitude of 8.0 on the moment magnitude scale (Mw), with its epicenter located some 100 km (62 mi) southwest of the capital Tokyo. The earthquake devastated Tokyo, the port city of Yokohama, and the surrounding prefectures of Kanagawa, Chiba, and Shizuoka, causing widespread damage throughout the Kantō region.