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

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。2006年11月15日和2007年1月13日的两次大地震（Mw=8.3）和里岛地震（Mw=8.1）使俯冲带地震活动中最明显的裂缝之一破裂，这是一条600公里长的库里尔弧段，大约一个世纪以来没有经历过一次大地震。这可能是迄今为止用空间大地测量方法观测到的最强的双重断层（俯冲界面上的逆冲断层和外隆起下的正断层）。千岛岛GPS连续站阵列是在大地震前几个月由俄罗斯和美国科学家共同努力安装的。阵列观测到的同震偏移量反演显示，2006年和2007年地震的最高滑动斑块或凸起彼此相邻。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重新分布引发的。我们正在探索压力变化并进一步触发。我们在提案中的目标是将GPS监测和理论分析扩展到事件发生后的3-4年至关重要的时期。在大地震发生后的最初几年中，只能通过连续观测来监测震后形变。2009年，我们安排了对地震后影响最大、无人居住的千岛群岛上所有连续监测站的访问，以确保它们正常工作，下载数据，并提供延长的电池供电。千岛地震双偶波后的震后形变表现为岩石圈下地幔摩擦后滑和应力粘弹性松弛的结合。地震后大约一年的过程很可能是粘弹性松弛。我们对这一过程的初步模拟表明，文献中提出的2004年苏门答腊-安达曼地震的地幔流变学不能解释千岛群岛双极子的震后数据。一旦我们在实地工作中获得另一年的时间序列数据以支持本建议，将对模型进行更充分的探索。该项目的长期目标是建立一个一致的模型，包括2006-2007年地震后的余震和粘弹性松弛，并将其与其他事件进行比较。我们将解决一个基本问题，即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？这个序列的震后模型是否与1952年堪察加半岛南部9级地震明显缺乏任何长时间的震后变形相一致？值得注意的是，最近几个月在库里尔中部发生了两次剧烈的构造事件：2009年1月15日外隆起下发生的Mw=7.4的逆冲地震和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获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、阿拉斯加费尔班克斯大学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预计将使人们普遍提高对俯冲带地震潜力的认识，并可能因此最终改善其他地方的灾害预测和减灾工作。

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.