Pre-20th Century of Earthquake Swarms and Volcanic Activity in the Higashi Izu Monogenetic Volcano Field, Based on Historical Documents

摘要

The pre-20th century history of earthquake swarms and volcanic activity in the Higashi Izu monogenetic volcano field, Japan, was ex- amined mainly by a critical review of historical documents. Four descriptions of historical earthquakes (in A. D. 1868 or 70, 18l6-17, 1737, and 1596) and two descriptions of possible vol- canic activity (in 1854 and 1777) were critically read and their reliabilities were checked. The 1868 (or 1870) earthquake (and possibly the 1816 -17 earthquake) corresponds to a historical an- alogue of the earthquake swarms off the east coast of Izu Peninsula, which occurred in l930 and have been episodically occurring since 1978. The recurrence intervals of these four earthquake swarms (1816-17, 1868 or 70, 1930, and 1978-present) are about 50-60 years. While the duration of each swarm is 1-4 months for the three swarms before 1978, the 1978-present swarm has episodically continued for at least 21 years. Two possible volcanic events in the Higashi Izu monogenetic volcano field were rejected because of lack of other reliable evidence.