INVESTIGATION OF EFFECTS OF SUBMARINE LANDSLIDE DURATION ON TSUNAMIS―RELATED TO THE YAEYAMA EARTHQUAKE IN 1771 WITH TSUNAMI PROPAGATION ANALYSIS―

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  • 1771年八重山地震における海底地すべり継続時間の影響評価

Abstract

<p> The Japanese Ministry of Education, Culture, Sports, Science, and Technology initiated the “Project for the Comprehensive Analysis and Evaluation of Offshore Fault Information” (The Project) in 2013. The objective of The Project is to contribute to assessment of earthquake and tsunami hazard in Japan’s seas by collecting offshore fault information. The Project collects and consolidates seismic profiling data using the latest data processing technology where offshore fault information is missing. The data are collected from various institutions that have conducted fault evaluation surveys in the seas around Japan. We reanalyzed the data and evaluated the faults using a consistent approach. The Project has reanalyzed the data of underground structures that were acquired by multiple institutions for the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and it has analyzed offshore fault information in the area of the southern Nansei Islands. In assuming the tsunami caused by the 1771 Yaeyama earthquake was associated with a submarine landslide, the present study reconstructed the shape of the shelf area around Yaeyama Islands and calculated the seabed deformation before the submarine landslide occurred. The maximum tsunami heights in the coastal area were calculated by applying the change directly in tsunami propagation analysis. The duration of the collapse of the assumed submarine landslide, which little is known about, submarine landslide was calculated using the Newmark sliding block method. A map of the geological structure of the seabed revealed that older Paleozoic age rocks are exposed from the Paleogene rocks on the slope. We analyzed the tsunami propagation caused by landslides using duration of landslides and found that the influence of duration affects coastal maximum tsunami heights, significantly.</p>

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