Collaborative Research: Coseismic slip, afterslip, and viscous relaxation in response to great 2006-2007 Kuril earthquakes: Evidence from the regional GPS network

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In 2006-2007, two great earthquakes ruptured a 600-km-long Kuril arc segment, one of the most conspicuous gaps in subduction-zone seismic activity. The earthquakes, the 15 November 2006 event with the thrust-faulting mechanism and the 13 January 2007 event with the extensional mechanism, had magnitudes 8.3 and 8.1, respectively. They make one of the largest earthquake doublets to occur in the era of space geodesy. The region of the central Kurils had not experienced a single great earthquake since 1915 despite a rapid plate convergence rate. In contrast, the segments to the north (Kamchatka) and south (the southern Kurils and Hokkaido) each had several great earthquakes within the last century. The Kuril subduction zone was never studied using space geodesy before 2006, when the research team of this project installed continuous GPS stations over the whole Kuril arc, several months before both great earthquakes in the central Kurils. In 2007, additional GPS stations were installed on the Kuril Islands accessible only by ship. In total, there are now seven functioning continuous stations and several sites measured by campaign surveys. The Kuril GPS network allowed the scientists to capture static coseismic offsets and rapid postseismic deformation at many sites, and to develop a preliminary model of coseismic slip distribution in earthquake ruptures. The current phase of the project enables a detailed study of the postseismic process following the 2006-2007 earthquakes. The focus of this phase is on acquiring and investigating irreplaceable data on the early postseismic transient signal. The project has the following goals: (1) develop improved coseismic slip models for the 2006-2007 events consistent with all available geodetic and seismic information; (2) develop a consistent model of postseismic deformation including both afterslip and viscoelastic relaxation, and compare to other events. The fundamental problems addressed here are: How long-lived is the postseismic deformation following great 2006-2007 Kuril earthquakes, and how does it compare with events at other subduction zones? Are postseismic models for the Kuril earthquake doublet consistent with the apparent lack of any long-lived postseismic deformation from the 1952 southern Kamchatka earthquake with a magnitude 9? The answers to these questions will help to make a step forward in understanding of the seismic cycle at subduction zones. The scientific results will directly contribute to earthquake hazard assessments by improving the accuracy of earthquake scenarios and probabilities for the Kuril subduction zone. This project continues and strengthens collaborative ties between US universities and the Russian Academy of Sciences