Application of paleodata for evaluation of the tsunami hazard of the Malokurilskaya bay coast (Shikotan Island)

Abstract

The data on the geological records of the paleotsunamis on the coast of one of the inhabited bays of Shikotan Island have been represented. The studied area is located on the side of the South Kuril Strait, which is currently being actively developed. The purpose of the article is to establish the chronology of the strongest tsunamis that occurred here in the middle-late Holocene, to evaluate their parameters and recurrence. Data on the sections of Holocene deposits, selected on lowland within head of the bay was also attracted. The diatom analysis was used as well as lithological study for identification of paleotsunami deposits. Tsunami sands include marine and brackish-water diatom species, benthic sublittoral forms predominate, the plankton sublittoral species has been found also. Finally, the oceanic diatoms, which came from deep-sea straits, have been represented in small numbers. The grain size composition of tsunami sands is very different depending on the sedimentation conditions existing on the coast: only thinner suspensions spread into the lake; sand sheets formed on the surface of the peat bog have a coarser composition and greater thickness. There are signs of active material feed from the slopes during some events. Paleotsunami age has been determined on the base of radiocarbon dating and tephrostratigraphy data. The lacustrine-swamp sequences included 2 layers of Tyatya Volcano tephra and 2 transit volcanic ash, the sources of which were eruptions of Tarumai and Mashu volcanoes, located on Hokkaido Island. The recurrence of strong tsunamis over the last ~7240 cal. has been established at first for the Malokurilsk village area, and the comparison of the obtained results was made with the results for Khromova, Otradnaya, Krabovaya bays and Pacific sides of the island. The paleo-events is proved to be more intense than the historical tsunami. The recurrence of large tsunamis which left sand sheets is less than that on the Pacific side of the island.