Structure of an active arc-continent collision area: the Aleutian-Kamchatka junction

The plate boundary between the North American and Pacific plates along the westernmost portion of the Aleutian are is formed by several active, dextra l strike-slip fracture zones. Fracturing is expressed by fault escarpments visible in reflection seismic profiles, and narrow zones of high seismicity . The seismicity changes from the Aleutian are, where shallow earthquakes o ccur, to intermediate to deep earthquakes in the Kamchatka-Aleutian junctio n area and to the south. In the vicinity of this junction, the distribution of earthquakes follows the traces of major Aleutian fracture zones down to a depth of 100 km. South of the Kronotsky Peninsula, the distribution of e arthquakes changes and is similar to other subduction zones. The fracture z ones cut the western Aleutian are into individual blocks, which move along strike-slip faults to the west and collide with Kamchatka. Related transten sion and transpression has led to the development of pull-apart basins and block tilting. The fracture zones splay into numerous strike-slip faults to the west, where they meet the Kamchatka margin. The main faults of the Ale utian fault system can be traced on the Kamchatka Mys Peninsula, where defo rmed Pleistocene sediments, high uplift rates, recent thrust faulting, and changes in the drainage system provide evidence for neotectonic activity. T he fault pattern onshore and offshore in the junction area supports an inde ntation tectonic model of the collision of Aleutian are slivers with Kamcha tka. (C) 2000 Elsevier Science B.V. All rights reserved.