SEGMENTIOLOGICAL STUDY OF MATERIAL TRANSPORT BY TSUNAMIS

点击翻译按钮获取中文摘要

Tsunamis have great hydrodynamic energy and have distinctive hydrodynamic effects on coastal regions. Recent geological studies have shown that a record of a tsunami inundation of a coast is preserved in tsunami deposits. Tsunamis transport large amounts of marine water and sediments inland, and seawater and sand invade coastal lakes and marshes. Moreover, tsunamis often move masses of rocks (Imamura et al., 2001), forming great onshore mounds or submarine bars. To interpret such tsunami records and estimate their ages, we must identify and study tsunami deposits. For example, multiple marine sand deposits found in excavations along the coast of northeast Japan suggest that repeated prehistoric and historic tsunami inundations affected the development of the coastal plain throughout the late Holocene (Minoura and Nakaya, 1991). However, the mechanisms of material transport -including the accumulation of thick mounds of marine sand and large-scale movement of huge rocks -by tsunamis are still unclear. Moreover, the topographic and geologic effects of tsunami sedimentation have never been fully considered, and the technological evaluation of tsunami sedimentation from the viewpoint of the impact on people and disaster planning is still insufficient. It has also been thought that earth-science methods cannot be applied to the study of tsunami deposits. In this context, many scientists, engineers, and historiographers have recently started coordinated studies on the recognition of tsunami deposits and on tsunami-induced material transport and environmental modification. Interdisciplinary studies of tsunami sedimentation will both clarify tsunami material transport mechanisms and establish criteria for theoretical understanding of the role of tsunamis in the development of coastal topography. The results of these studies will be applied to actual tsunami events, and will enable the specific disaster assessment of future tsunami inundations.