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

2006年11月15日和2007年1月13日发生在千岛群岛的Mw=8.3和Mw=8.1的大地震破坏了俯冲带地震活动中最明显的空白之一，一个600公里长的Ku-ril弧段，大约世纪没有经历过一次大地震。它可能是空间大地测量方法所观测到的最强的双重（俯冲界面上的逆冲断层，然后是外部隆起下的正断层）。作为俄罗斯和美国科学家的合作成果，千岛群岛GPS连续站阵列在大地震前几个月安装。对阵列上观测到的同震偏移量的反演显示，2006年和2007年地震的最高滑动斑块或凸体彼此相邻。这种相关性表明，2007年的伸展事件是由2006年逆冲事件后的应力再分散触发的。我们正在进一步探索应力变化和触发机制，我们的建议目标是将GPS监测和理论分析扩展到事件发生后的3-4年这一至关重要的时期。在大地震发生后的最初几年，震后变形只能通过连续观测来监测。2009年，我们计划访问位于无人居住的千岛群岛中部的所有连续观测站，那里的震后影响最大，以确保它们正常工作，下载数据，并提供延长的电池电源。千岛地震后的变形代表了岩石圈下地幔的摩擦后滑和粘弹性应力松弛的组合。地震后一年左右的普遍过程可能是粘弹性松弛。我们对这一过程的初步模拟表明，2004年苏门答腊-安达曼地震文献中提出的地幔流变学不能解释千岛双联体的震后数据。一旦我们在本提案所支持的实地工作中获得另一年的时间序列数据，将更充分地探讨模型。该项目的一个长期目标是开发一个一致的模型，包括2006-2007年地震后的后滑和粘弹性松弛，并将其与其他事件进行比较。我们将解决一个基本问题，2006-2007年千岛群岛大地震后的震后变形持续多久，与其他俯冲带的事件相比如何？该序列的震后模型是否与1952年南堪察加Mw 9地震明显缺乏任何长期震后变形相一致？ 值得注意的是，近几个月来，库里尔斯中部发生了两次剧烈的构造事件：2009年1月15日外隆下的Mw=7.4逆冲地震和2009年6月11日马图阿岛的火山爆发。我们假设我们的网络捕捉到了与这两个事件相关的表面变形。这个项目是由哥伦比亚大学、阿拉斯加大学费尔班克斯分校和俄罗斯科学院研究所合作完成的。该项目将继续并加强美国和俄罗斯科学家之间的合作关系。该项目的成果将对遭受灾难性地震的地区产生影响。这项工作的结果和我们将开发的方法有望普遍提高对俯冲带地震潜力的认识，从而最终提高其他地区的灾害估计和减灾能力。

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.