The 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 Sengoku period.
Tectonic setting
The island of Honshu is situated in a region of complex plate convergence between the Pacific, Amurian, Philippine Sea and Okhotsk Plates. While a large component of the convergence is accommodated by subduction along the Nankai and Japan Trenches, shallow intraplate deformation occur as well. The Japan Median Tectonic Line and Itoigawa-Shizuoka Tectonic Line are two major fault zones that accommodate this deformation. These faults are associated with strike-slip and dip-slip faulting.
Earthquake
The origin of the Tenshō earthquake is not known, but geologists have presented different faults to be the possible source. There is still debate about which fault zone caused the earthquake and even how did the earthquake unfold, through a single fault system rupture or even a multiple fault system rupture, given the massive death and destruction across wide areas of the Tōkai, Kinki, and Hokuriku regions. An analysis of the meizoseismal area suggest the source area was approximately extending north-northeast–south-southwest from Wakasa Bay to Ise Bay. The same region was also the source area of the 1891 Mino–Owari earthquake.
Geology
The Atera Fault System that runs through the Chūbu region is a north-northeast–south-southwest-striking left-lateral fault with a length of that ruptured during the event. Present data suggest seismicity on the fault is low, with long recurrence intervals between major earthquakes of ~1,800 years. Soil surveys have found evidence that the fault ruptured in 1586. The forested area in the region showed evidence of en-echelon fractures. A nearby sag pond is also thought to have formed from the earthquake that has now been converted into a paddy field. Paleoseismic trenching and radiocarbon dating revealed that the last seismic event on the fault occurred between 1400 and 1600. This date corresponded to the 1586 earthquake as no other reports of a severe earthquake in the region occurred at around this time. Further surveys revealed that another structure, the Miboro Fault, a northwest strand of the Atera Fault was also involved in the earthquake, bringing the estimated rupture length to . The suggested epicenter is located near the northwest part of Gifu Prefecture, based on analyzing the damage distribution.
Additional surveys and drilling found that the Yōrō-Kuwana-Yokkaichi Fault Zone to the west of the Nōbi Plain may have also ruptured, and corresponds to reports of severe damage in the vicinity. There is also evidence that the last earthquake on that fault zone could have happened between the 13th and 16th century, and it hence corresponds to the time of the earthquake (1586). The Yōrō-Kuwana-Yokkaichi Fault Zone is a group of three reverse faults beneath the Nōbi Plain with a total length of . Evidence of faults was further supported by the presence of vertical displacements reflected in the sedimentary layers of the plain. The fault zone was also responsible for an earthquake in 745 AD (ja), and ten additional events within the past 6,000 years. The blind Yōrō Fault located along the eastern base of the Yōrō Mountains was also identified as a source of the quake. Fold scarps measuring up to high formed during the event was discovered to have extended in length.
The disappearance of islands at the mouth of the Kiso River in Ise Bay was attributed to liquefaction and tsunami, caused by slip on the Ise Bay and Ise Bay Mouth Faults, located undersea.
Foreshocks and aftershocks
A foreshock occurred on November 27, 1585 and is thought to have triggered the mainshock two months later. The foreshock had an estimated magnitude of 6.6. The earthquake caused aftershocks that were felt in Kyoto every day for two months. Two strong earthquakes rocked the region in 1589 and 1596 (ja), but were less destructive. The latter event had a magnitude of 7.5 and resulted in at least 1,100 fatalities in Kyoto and Sakai.
Tsunami
A tsunami was reported in Lake Biwa, Wakasa Bay and Ise Bay, however these may have been seiches as the rupture did not extend offshore. A run-up height of was recorded at Ise Bay, while at Wakasa Bay, the tsunami was estimated to be .