Micro-bathymetric evidence for the effect of submarine mass movement on tsunami generation during the 2009 suruga bay earthquake, Japan

Abstract

A moderate earthquake (Mw 6.4) caused a submarine mass movement in Suruga Bay, Japan on 11th August, 2009. The earthquake was also accompanied by a tsunami, which was observed at various observatories around Suruga Bay. A micro-bathymetric map was obtained from an autonomous underwater vehicle (AUV) survey of Urashima in the area where the submarine mass movement occurred. The Urashima cruised close to the seafloor and collected very high resolution bathymetric data as a raster graphic image with pixels arranged in a 1 m by 1 m square grid. The 3D seafloor image obtained clearly shows an escarpment (450 m wide and 10-15 m deep) approximately 5 km off the coast. Bedforms which were considered to have been formed due to earthquake-induced turbidity currents, spread wide in the survey area. The bedforms appear at about 20-30 m interval, and are lower than 1 m in height. A numerical simulation of the tsunami assuming that the fault motion and submarine mass movement occurred simultaneously provided a better match with the tsunami observation records at Yaizu tidal station and other stations than a simulation based on fault motion alone. © Springer Science+Business Media B.V. 2012.