Tensho earthquake is one of the most famous large inland earthquakes during the medieval times of Japan. It occurred on Jan. 18, 1586 in Chubu district. It was almost the equal size to Nobi earthquake in 1891, and we estimated its size is around M7.8-8.0. Many major active faults in Chubu district had been assigned as the source faults of this earthquake. However, the careful examination of the historical materials, and the precise analysis of the distribution of estimated reliable seismic intensities revealed that it is impossible to cause the damage of whole Tensho earthquake by a single earthquake of M8-class. The main shock occurred in the south-western part of Nobi basin. The source faults are narrowed down to some faults near Yoro and Suzuka mountains, and Ise Bay, or southern part of Yanagase, Sekigahara, and nearby faults, when we compare the intensity distribution with expected ones for several major fault groups in Chubu district. The famous destruction of Uchigashima Family in Kiun Castle and the crushing death of Mr. and Mrs. Ukon Maeda in Kifune Castle were caused by the different earthquake, which occurred on Jan 16, in some faults near Shokawa River, and its size was around M7.0 ±0.2. In order to reveal source faults of medieval destructive earthquakes, which usually have too few historical materials, we have to be careful to the credibility of information. Those written in later years may be modified through folklore transmission. Even in the primary historical sources such as a diary of an aristocrat or a letter by a missionary, hearsay information in remote area was left with true damages they really knew. Since there are much more destructive earthquakes than those known in the catalogue we have now, the trench results should not be restricted to select the candidate of earthquakes only from the current earthquake catalogue. For example, July 31, 1585, a very strong earthquake was felt in Mikawa, Ise, and Kyoto, and no destructive damage was known in Chukyo area. This must be the first candidate for the latest activity of Atera fault.
