Tsunami trace survey on the Bonin Islands for revealing recurrence history of great earthquakes in the Izu-Bonin subduction zone

2016 Fiscal Year Final Research Report

• Project/Area Number: 26750129
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Natural disaster / Disaster prevention science
• Research Institution: The University of Tokyo
• Principal Investigator: Harada Tomoya 東京大学, 地震研究所, 特任助教 (30452501)
• Project Period (FY): 2014-04-01 – 2017-03-31
• Keywords: 津波堆積物 / 津波石 / 津波痕跡調査 / 小笠原諸島 / 伊豆-小笠原海溝 / 巨大地震 / 1605年慶長地震

Outline of Final Research Achievements

The Izu-Bonin subduction zone has been regarded as so-called ”Mariana-type subduction zone” where M>7 interplate earthquakes did not occur inherently. Ishibashi and Harada (2013) and Harada et al. (2013) proposed a hypothesis that the 1605 Keicho earthquake was a giant/great earthquake along in the Izu-Bonin subduction zone from re-examination of historical documents and tsunami numerical simulation. In order to confirm their hypothesis, we performed tsunami trace survey on the Bonin Islands. As a result, we discovered more than 3 tsunami deposit layers at the Sakai-ura beach and 4-5 tsunami deposit layers at the river mouth of the Yatsuse River in the Chichi Island. C14 dating shows these layers deposited in 17-18 A.D. However, we could not identify the 1605 tsunami deposit from these layers due to the dating accuracy.

Free Research Field

地震学