Understanding historical and pre-historical earthquakes is essentially important in estimating site, magnitude and timing of future earthquakes. Records are supplied mostly from historical documents we have in Japan dating from about 1, 300 years ago and from natural records found in topography and geological formations in earthquake areas. The usefulness of collating historical and natural records is shown from some historical earthquakes. For example, the Tsukushi Earthquake of AD. 679 was reasonably inferred to have occurred from the Minoh fault zone in Fukuoka Prefecture, Kyushu, based on historical documents and on data from excavations of the ground just on the fault line.
Dating the last activity of an active fault is indispensable for the long-term prediction of earthquakes. For example, the AD. 1596 earthquake was revealed by ground excavations to have occurred from the Arima-Takatsuki fault zone. This means a significant decrease in the possibility of a large earthquake in the near-future at the location.
The concept of the characteristic nature of the size and the recurrence timing of the earthquake from a fault, on which long-term prediction is currently based, was derived from good examples of fault activity recorded on Japanese historical documents and nature.