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

2006年至2007年，两次大地震使600公里长的千岛岛弧段破裂，这是俯冲带地震活动中最明显的间隙之一。2006年11月15日的逆冲断层和2007年1月13日的伸展机制地震，震级分别为8.3级和8.1级。它们造成了空间大地测量学时代发生的最大的双重地震之一。自1915年以来，尽管板块收敛速度很快，但千岛群岛中部地区没有经历过一次大地震。相比之下，北部（堪察加半岛）和南部（南千岛群岛和北海道）在上个世纪都发生了几次大地震。在2006年之前，人们从未使用空间大地测量学研究过千岛群岛俯冲带。2006年，在千岛群岛中部两次大地震发生的几个月前，这个项目的研究小组在整个千岛岛弧上安装了连续的GPS站。2007年，在千岛群岛安装了更多的GPS站，只能通过船只进入。目前总共有7个连续运作的监测站和几个通过运动调查测量的站点。千岛岛GPS网络使科学家们能够捕捉到许多地点的静态同震偏移量和震后快速变形，并建立了地震破裂处同震滑动分布的初步模型。该项目的当前阶段能够对2006-2007年地震后的地震过程进行详细研究。该阶段的重点是获取和研究不可替代的早期地震后瞬态信号数据。该项目有以下目标：(1)根据所有可用的大地测量和地震信息，开发改进的2006-2007年地震同震滑动模型；(2)建立包括余震和粘弹性松弛在内的震后形变一致模型，并与其他事件进行比较。这里要解决的基本问题是：2006-2007年千岛岛大地震后的震后变形持续多久？与其他俯冲带的地震事件相比如何？千岛群岛地震的震后模型是否与1952年堪察加南部9级地震明显缺乏任何长时间的震后变形相一致？这些问题的答案将有助于进一步了解俯冲带的地震周期。这些科学成果将通过提高千岛岛俯冲带地震情景和概率的准确性，直接为地震危险性评估做出贡献。该项目继续并加强了美国大学与俄罗斯科学院之间的合作关系

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