SEISMOTECTONICS AND EVOLUTION OF SOLDATSKAYA BAY (KAMCHATKA) DURING THE HOLOCENE E.A. Kravchynovskaya1, T.K. Pinegina2, Joanne Bourgeois3, Kevin Pedoja4 Moscow State University, Russia. E-mail: firstname.lastname@example.org 2 Institute of Volcanology & Seismology FEB RAS, Russia. E-mail: email@example.com 3 University of Washington, USA. E-mail: firstname.lastname@example.org 4 University of Paris, France. E-mail: email@example.com 1 In 2003 we conducted detailed research on the Holocene seismotectonic evolution of Soldatskaya Bay, Kamchatka. The bay is located between two tectonic «blocks», which constitute Kamchatsky Mys Peninsula. The southern block represents a part of the island arc front and is located at the junction of the Kurile-Kamchatka and Aleutian arcs . This block is characterized by rapid uplift (up to 1 cm per year during the Late Holocene) [3, 4]. The northern block is located beyond the active subduction zone. It is characterized by rather slow differentiated movements. During our paleoseismological research in Soldatskaya Bay we have found thatthe main factors influencing its evolution in the Holocene were differentiated tectonic movements, which have been studied based on morphology, geological structure and ages of the beach ridges and marine terraces [2, 4]. Ages of the coastal landforms have been determined based on tephrochronology [5, 6]. The resulting direction of tectonic movements in Soldatskaya Bay during the last 6000 years is positive at an average rate of ~0.1 cm/yr. Tectonic movements within the interval of 6-4 ka BP are difficult to assess. We suggest that during this time some subsidence of the Holocene terrace occurred. Alternatively, there is some evidence in the North Pacific for a mid-Holocene highstand. Starting Soldatskaya Bay from ~4 ka BP and up to 1854 the bay has been experiencing tectonic uplift. During the period from 1950 BC to 250 AD its average rate was 0.04 cm/yr; during the period from 250 AD to 590 AD - 0.23 cm/yr; and from 590 to 1854 AD - 0.1 cm/yr. From 1854 to 1964 the bay experienced rapid subsidence at an average rate of 1.2 cm/yr. As we see, periods of rapid uplift in Soldatskaya Bay alternated Cape Kamchatskiy with periods of slow uplift or even subsidence. Rates of tectonic movements were different in south and north parts of the bay. The time intervals were singled out based on dated tephra layers preserved in the coastal sections. The data obtained have allowed us to document not only differentiated tectonic movements but also large coseismic deformations related to individual strong earthquakes. In Soldatskaya Bay, abrupt vertical deformations of the surface have resulted in the formation of numerous beach ridges. The shorter the time interval we choose for our calculations, the larger the calculated amplitude of the vertical movements. This is explained by the fact that regarding long intervals, we get an average rate of movements, and are not able to single out individual seismic events. Based on seismotectonic studies and field data we have compiled a paleogeomorphological sketch map of the Soldatskaya Bay coast and adjacent area and reconstructed key events in its Holocene history. This work was support by : Russian Academy of science (grant # 03-05-64584, # 03-05-78027) & National Scientific Foundation (grant # № EAR 0125787). References 1. 2. 3. 4. 5. 6. Avdeiko G.P., Popruzhenko S.V., Palueva A.A. Modern structure of the KurileKamchatka region and magma-forming conditions/ Geodynamics and volcanism of the Kurile-Kamchatka island-Arc-System. Petropavlovsk-Kamchatski., 2001 (in Russian). Kravchynovskaya E.A. The history and development factors of Soldatskaya Bay (Kamchatskiy Cape Peninsula) in Holocene/ Abstract for International student conference, Moscow, MSU, 2004 (in Russian). Melekestsev I.V., Kurbatov A.V., Pevzner M.M., Sulergitskiy L.D. Prehistoric tsunamis & strong earthquakes at Kamchatskiy Cape Peninsula (Kamchatka) by tephrohronological studies/ Volcanology & seismology, Vol. 4-5, 1994 (in Russian). Pinegina T.K. Tsunamies on the Pacific coast of Kamchatka for the last 7000 yr.: the diagnostics, dating, frequency/ Geodynamics and volcanism of the Kurile-Kamchatka island-Arc-System. Petropavlovsk-Kamchatski., 2001 (in Russian). Braitseva O.A., Ponomareva V.V., Sulerzhitsky L. D., Melekestsev I.V., Bailey J. Holocene key-marker tephra layers in Kamchatka, Russia // Quaternary Research. 1997. V.47. Pinegina T.K., Bourgeois J., Bazanova L.I., Melekestsev I.V., Braitseva O.A., A millennial-scale record of Holocene tsunamis on the Kronotskiy Bay cost, Kamchatka, Russia // Quaternary Research. 2003. V. 59.