HR: 0800h
AN: H41C-0315    [Abstracts]
TI: Active-Margin Coastal Morphology as a Reflection of Holocene Seismotectonic Evolution: An Example From Eastern Kamchatka, Southwestern Bering Sea
AU: Kravchunovskaya, E
EM: katja832003@mail.ru
AF: Dept. of Geomorphology, Moscow State University, Moscow, 119899 Russian Federation
AU: Pinegina, T
EM: pinegtk@kcs.iks.ru
AF: Inst. of Volcanology & Seismology FED RAS, Piip Blvd. 9, Petropavlovsk-Kamcha, 683006 Russian Federation
AU: * Bourgeois, J
EM: jbourgeo@u.washington.edu
AF: Dept. Earth & Space Sciences, Univ. of Washington, Seattle, 98195-1310 United States
AB: We studied the Holocene seismotectonic evolution of Soldatskaya Bay, Kamchatskiy Peninsula, Kamchatka, via coastal geomorphology and morphodynamics. In this bay we examined morphology, geological structure and ages of beach ridges, which compose a marine terrace. Each relic beach ridge marks the position and altitude of the shoreline at the time when it completes its formation. In areas of active Holocene volcanism it is possible to estimate the age of beach ridges using tephrochronology, because sandy soils overlying the beach ridges contain multiple ash layers, most of which have been mapped and dated. So the beach ridges (morphology of marine terraces) can reflect the changes of relative sea level in time. In general these changes may be caused by eustatic or tectonic movements. For the last 5000 years in the eastern Kamchatka region, the difference in elevation of the beach ridges commonly marks the difference in sea level caused by strong seismotectonic movements. If the hydrodynamic conditions during the formation of the beach ridges are similar, and other factors can be eliminated, the difference in their elevations is the net amplitude of tectonic deformation during the time interval between their formation. For Soldatskaya Bay we measured the elevations and estimated the ages of beach ridges spanning nearly 5000 years from the present. Based on the obtained data a paleogeomorphological reconstruction of Soldatskaya Bay was carried out. From this reconstruction, we calculated average rates of relative sea level change and progradation in time intervals bracketed by marker tephra. Estimated relative sea level change differs between the southern and northern parts of the Bay, pointing to seismotectonic control. Rates also vary in time. Higher rates were estimated for shorter time intervals, with slower rates characterizing longer time intervals. This happens because long time periods are represented by average seismotectonic rates which mask short-term, high-amplitude coseismic deformation related to individual earthquakes.
DE: 8404 Ash deposits
DE: 7221 Paleoseismology
DE: 4556 Sea level variations
DE: 3020 Littoral processes
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting