Holocene tsunamis in the southwestern Bering Sea, Russian Far East, and their tectonic implications

Abstract

The Bering Sea coast of Kamchatka overlies a boundary between the proposed Okhotsk and Bering blocks, or (micro)plates, of the North American plate in the Russian Far East. A history of tsunamis along this coast for the past 4000 yr indicates that the zone north of the Kuril-Kamchatka subduction zone produces tsunamigenic earthquakes every few centuries. Such a record is consistent with convergence of the proposed Okhotsk and Bering blocks along the Bering Sea coast of Kamchatka. A tsunami deposit from the 1969 Mw 7.7 Ozernoi earthquake helps us interpret older tsunami deposits. Newly studied tephra layers from Shiveluch volcano as well as previously established marker tephra layers in northern Kamchatka provide age control for historic and prehistoric tsunami deposits. Based on >50 measured sections along 14 shoreline profiles, tsunami-deposit frequencies in the southwestern Bering Sea are about five per thousand years for tsunamis generated north of the Kuril-Kamchatka trench.