HR: 0800h
AN: T41C-1228    [Abstracts]
TI: Variability in Coastal Neotectonics Along the Kamchatka Subduction Zone
AU: * Bourgeois, J
EM: jbourgeo@u.washington.edu
AF: Dept. Earth & Space Sci., Univ. of Washington, Seattle, WA 98195-1310 United States
AU: Pinegina, T
EM: pinegtk@kcs.iks.ru
AF: Inst. Volcanology & Seismology, Piip Blvd. 9, Petropavlovsk-Kamcha, 683006 Russian Federation
AU: Ponomareva, V
EM: ponomareva@ginras.ru
AF: Inst. Volcanology & Seismology, Piip Blvd. 9, Petropavlovsk-Kamcha, 683006 Russian Federation
AB: The eastern coast of Kamchatka can be divided into several morphotectonic zones, which appear to correspond primarily to variations in the subducting crust, rather than to characteristics of the subduction zone such as rate of subduction or subduction angle. Pleistocene marine terraces and Holocene coastal stratigraphy along Kamchatka show variability in uplift (and subsidence) rate both at the degree-latitude scale, and at a scale of kilometers to 10s of km. The southern coast (51-53$^{o}$N, to Petropavlovsk) is primarily rocky headlands with narrow embayments, some filled with volcaniclastics. North of Petropavlovsk, the coast is subdivided into a series of broad embayments separated by four peninsulas--Zhupanovskiy, Kronotskiy, Kamchatskiy, Ozernoi, from south to north. These peninsulas are landward, respectively, of the Kruzenstern fracture zone, the Meiji seamounts, the Aleutian-Komandorskiy island chain, and the Beta Rise. Our field studies of Quaternary coastal evolution and seismotectonic regime over the last decade have included: 1) tephra chronology for dating and correlation 2) study of paleotsunami deposits to estimate recurrence rates of tsunamigenic earthquakes; and 3) analysis of the modern and paleo-topography of marine terraces and beach ridges in order to determine the direction and intensity of tectonic deformation over different spatial and temporal scales. The shorter the time interval we are able to specify (decades to hundreds of years), the higher the rate of vertical movements we tend to obtain. Estimates of net deformation for longer periods (10s to 100s of thousands of years) are commonly an order of magnitude slower, because seismic cycles are averaged out. The net Quaternary deformation of eastern Kamchatka is uplift, with peninsulas exhibiting the highest rates, up to 2 mm/yr for the last 0.5 my on Kamchatskiy Peninsula. The large embayments between peninsulas typically exhibit evidence for subsidence or stasis on a Holocene time scale. On Kamchatskiy Peninsula (56-56.7$^{o}$N), we have enough field sites to show that there is a similar (fractal?), smaller-scale segmentation of deformation. But why the nature of south Kamchatka, and the transition to the Kuril Islands?
DE: 8105 Continental margins and sedimentary basins
DE: 8150 Plate boundary--general (3040)
DE: 8155 Plate motions--general
DE: 8158 Plate motions--present and recent (3040)
DE: 3020 Littoral processes
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting