Abstract
Paleotsunami is one of the indicators for reconstruction of paleoearthquakes. It has been generally considered that the east coast of Taiwan has not been affected by large tsunami, due to the absence of documented records in the short historical time, and also due to steep offshore submarine morphology. A legend of the Ami tribe says, however, that strong waves have rushed toward the northern part of the east coast.In addition, a local historian tells a story that a sudden disappearance of vegetation has occurred at Chenggong town at ca. 150 years ago. We infer that this environmental change may record a tsunami event on this coast and wish to confirm the occurrence of tsunami by excavation of Holocene deposits. The excavated sites are located on the lower Holocene marine terraces at 15-20 m asl at Chenggong area. The first excavation was done by hand-augering on Sept. 2009, and the second one was by using Geoslicer at four sites on March, 2010. In addition, we have observed coastal feature along the east coast of Honchuan Peninsula. This preliminary report provides two lines of geological evidences for possible tsunami origin. One is the presence of two abrupt facies changes from terrestrial condition to marine or brackish condition, event I and II, at Site 1. Available radiocarbon date suggests the event I occurred at 1850 to 1600 cal yr BP, thus event II is further younger than this age. We are working on various kinds of analysis, including radiocarbon dating, to confirm the tsunami origin for observed features.
