Collaborative Research: Postseismic deformation of the Earth after the great 2006-2007 Kuril earthquake doublet: Implications for mantle rheology

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The great 15 November 2006 Mw=8.3 and 13 January 2007 Mw=8.1 Kuril earthquakes rup-tured one of the most conspicuous gaps in subduction-zone seismic activity, a 600-km long Ku-ril arc segment that had not experienced a single great earthquake for about a century. It is probably the strongest doublet (thrust faulting on a subduction interface followed by normal faulting beneath the outer rise) ever observed by space geodetic methods. The Kuril GPS Array of continuous stations was installed several months before the great earthquakes as a collabora-tive effort of Russian and US scientists. Inversions of coseismic offsets observed on the array showed that highest-slip patches, or asperities, from the 2006 and 2007 earthquakes are adjacent to each other. This correlation suggests that the 2007 extensional event was triggered by redis-tribution of stresses following the 2006 thrust event. We are exploring the stress changes and triggering further.Our target in the proposal is to extend the GPS monitoring and theoretical analysis to a cru-cially important period of 3-4 years since the events. In the first few years after a great earth-quake, the postseismic deformation can only be monitored by continuous observations. In 2009, we schedule visits to all continuous stations on uninhabited central Kuril islands, where the postseismic effect is the greatest, to guarantee that they are working, download data, and pro-vide the extended battery power supply. The postseismic deformation following the Kuril earthquake doublet represents a combination of frictional afterslip and viscoelastic relaxation of stresses in the sublithospheric mantle. The process prevailing after about one year since the earthquake is likely to be viscoelastic relaxation. Our preliminary modeling of this process shows that the mantle rheology proposed in literature for the 2004 Sumatra-Andaman earth-quake cannot explain the postseismic data from the Kuril doublet. Models will be explored more fully once we have obtained another year of time series data in the field work to be supported by this proposal. A long-term goal of the project is to develop a consistent model including both afterslip and viscoelastic relaxation following the 2006-2007 earthquakes, and compare this to other events. We will address a fundamental problem, How long-lived is the postseismic de-formation following great 2006-2007 Kuril earthquakes, and how does this compare with events at other subduction zones? Are postseismic models for this sequence consistent with the appar-ent lack of any long-lived postseismic deformation from the 1952 Mw 9 southern Kamchatka earthquake? It should be noted that two dramatic tectonic events happened in the central Ku-rils within recent months: the 15 January 2009 Mw=7.4 thrust earthquake beneath the outer rise and the 11 June 2009 volcanic explosion on Matua Island. We suppose our network captured surface deformations associated with both events.This project is a collaboration involving Columbia University, the University of Alaska Fair-banks, and institutes of the Russian Academy of Sciences. The project will continue and strengthen collaborative ties between US and Russian scientists. The results of the project will have an impact on the region subject to disastrous earthquakes. The results from this work and the methods we will develop are expected to lead to generally improved understanding of the earthquake potential of subduction zones and may thus ultimately lead to improved hazard es-timation and mitigation elsewhere.