Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4718239 | Marine Geology | 2014 | 10 Pages |
Abstract
This article describes the bedforms formed by the 2011 Tohoku-Oki tsunami on the southern Sendai Plain, NE Japan. Integrated analyses of satellite images, field survey data, and X-ray radiographs revealed the natural shapes of these bedforms. The dominant bedforms are dunes and antidunes about ~Â 20Â cm thick (high) and relatively flat because of their meter-scale wavelengths. Their morphologies reflect mainly the tsunami run-up flow on the flat lowland and the return flow in a narrow, steep valley. Flow depth changed at sites where the level of the ground surface changed along the tsunami flow path, causing the flow velocity to fluctuate. Flow velocity decreased in depressed (deep-water) sections and increased in raised (shallow-water) sections. The types and positions of the tsunami deposit bedforms were thus strongly controlled by local ground surface roughness, such as raised roadbeds and levees. As a result, the observed thickness distribution of the tsunami deposits fluctuates. It is important to consider the possible existence of bedforms in paleotsunami surveys, especially for accurate determination of the thickness distribution of the tsunami deposits, because thickness data are essential information for reconstruction of the tsunami inundation limit as well as its flow speed.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
Osamu Fujiwara, Koichiro Tanigawa,