Candidate Hyūga-nada Earthquakes in the Early Modern Period of Japan

Abstract

This study investigates earthquakes whose epicenters were possibly located in the Hyūga-nada region during early modern Japan, particularly the Edo period, based on the characteristics of seismic intensity distributions from both felt reports and instrumental observations compiled by the Japan Meteorological Agency. Historical earthquake records from southern Kyushu have traditionally been limited due to the scarcity of surviving documents, and their number has not been considered sufficient for detailed seismic analysis. To address this gap, newly uncovered historical records were utilized in the present study. Earthquakes were selected for analysis when seismic shaking was confirmed in at least three of the following locations: Miyazaki, Oita, Kagoshima, and Uwajima in Ehime Prefecture. The estimation of epicenters was carried out while taking into account the reliability of each historical source. In addition to the two well-known earthquakes of 1662 and 1769, it was confirmed that the earthquakes of 1698 and 1844 showed intensity distributions similar to those typically associated with Hyūga-nada earthquakes. Moreover, previously unclassified earthquakes, such as the 1843 event newly revealed through recent historical research, were examined. These findings help fill significant gaps in the seismic record for southern and central Kyushu. This study contributes to a more comprehensive reevaluation of earthquake activity during early modern Japan and is expected to provide a solid foundation for future seismic hazard assessments.