The magnitude 7.9 Tenshō earthquake strikes Honshu, Japan, killing 8,000 people and triggering a tsunami.

The Tenshō earthquake occurred in Japan on January 18, 1586, at 23:00 local time. This earthquake had an estimated seismic magnitude of 7.9, and an epicenter in Honshu's Chūbu region. It caused an estimated 8,000 fatalities and damaged 10,000 houses across the prefectures of Toyama, Hyōgo, Kyōto, Osaka, Nara, Mie, Aichi, Gifu, Fukui, Ishikawa and Shizuoka. Historical documentation of this earthquake was limited because it occurred during the tumultuous Sengoku period.

Honshu , historically known as Akitsushima , is the largest of the four main islands of Japan. It lies between the Pacific Ocean (east) and the Sea of Japan (west). It is the seventh-largest island in the world, and the second-most populous after the Indonesian island of Java.

A tsunami is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind, or tides, which are in turn generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water from a large event.

January 18 is the 18th day of the year in the Gregorian calendar; 347 days remain until the end of the year.