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

2006-2007年，两次大地震使600公里长的千岛弧段破裂，这是俯冲带地震活动最明显的空白之一。2006年11月15日的逆冲断层地震和2007年1月13日的伸展地震震级分别为8.3级和8.1级。它们是空间大地测量学时代发生的最大的地震双峰之一。自1915年以来，千岛群岛中部地区没有经历过一次大地震，尽管板块聚合速度很快。相反，北部（堪察加半岛）和南部（南千岛群岛和北海道）在上个世纪都发生过几次大地震。在2006年之前，从未使用空间大地测量学研究过千岛俯冲带，当时该项目的研究小组在整个千岛弧上安装了连续的GPS站，这是在千岛群岛中部两次大地震发生前几个月。2007年，在千岛群岛安装了更多的全球定位系统站，只有船只才能进入。目前共有7个连续运作的监测站和几个通过运动调查衡量的地点。Kuril GPS网络使科学家能够捕获许多地点的静态同震偏移和震后快速变形，并开发出地震破裂中同震滑动分布的初步模型。该项目的当前阶段能够对2006-2007年地震后的震后过程进行详细研究。这一阶段的重点是获取和调查震后早期瞬态信号的不可替代数据。该项目有以下目标：（1）为2006-2007年的地震开发与所有现有大地测量和地震信息相一致的改进的同震滑动模型;（2）开发一个一致的震后变形模型，包括后滑和粘弹性松弛，并与其他地震进行比较。这里要解决的基本问题是：2006-2007年千岛群岛大地震后的震后变形有多长，它与其他俯冲带的事件相比如何？千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期震后变形相一致？对这些问题的回答将有助于进一步了解俯冲带的地震周期。科学成果将通过提高千岛俯冲带地震情景和概率的准确性，直接有助于地震危险评估。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