Collaborative Research: Strain accumulation and release at the Kuril subduction zone from postseismic observations on the Kuril GPS array in 2007-2014

位于太平洋西北部的1,200公里长的千岛巨型逆冲断层是地球上地震最活跃的地区之一。这是最后一个完全没有用空间大地测量方法探测的主要俯冲带。2006年？2007年，该地区发生的两次大地震部分破坏了俯冲带地震活动中最明显的空白之一（2006年11月15日Mw 8.3逆冲事件和2007年1月13日Mw 8.1伸展事件）。2009年1月15日在同一地区发生的一次7.4级逆冲大地震表明地震危险性增加。Kuril GPS阵列是在2006年之前几个月安装的？2007年美国和俄罗斯科学家合作的地震。观测记录了千岛大地震后的同震和震后地表变形。这个项目的最后阶段的直接重点是获取不可替代的，瞬态震后数据跨越时间段2007？2014.该项目将继续与美国大学和俄罗斯科学院的机构合作。2011年使我们能够开发同震滑动模型和震后机制模型。结果表明，震后运动主要是由弱麦克斯韦粘性软流圈中剪应力的粘弹性松弛引起的。根据其他震后研究的经验，较长的时间序列将使我们能够开发出更强大的震后变形模型和俯冲界面上的震间摩擦耦合模型。需要完整的8年数据集来解决基本问题：在2006年和2007年千岛地震的同震和震后，太平洋板块俯冲到北美板块（鄂霍次克海）之下所产生的应变有多少被释放出来？是否有可能解释地震后的表面变形在千岛俯冲带与线性粘性地幔或应力依赖流变学是必需的？这些问题在2011年东北部9.0级大地震之后尤为重要，这使得科学家们质疑大地震的传统前兆的有效性：地震空区的位置和凹凸体的位置（俯冲界面处的高摩擦锁定斑块）。

The 1,200-km-long Kuril megathrust in the northwest Pacific Ocean is one of the most seismically active regions on the Earth. It was the last major subduction zone totally unexplored by methods of space geodesy. In 2006?2007, a doublet of great earthquakes in this region partly ruptured one of the most conspicuous gaps in subduction-zone seismic activity (the 15 November 2006 Mw 8.3 thrust event and the 13 January 2007 Mw 8.1 extensional event). A large 15 January 2009 Mw 7.4 thrust earthquake in the same region demonstrated the heightened seismic hazard. The Kuril GPS Array was installed several months before the 2006?2007 earthquakes in collaboration between US and Russian scientists. Observations on the array documented coseismic and postseismic surface deformation following the great Kuril earthquakes. The immediate focus of this final phase of the project is on acquiring irreplaceable, transient postseismic data spanning the time period 2007?2014. This project will continue collaboration between US universities and institutions of the Russian Academy of Sciences.The data from the Kuril GPS Array collected in 2006?2011 allowed us to develop models of coseismic slip and models of postseismic mechanisms. It was shown that most of the postseismic motion was caused by the viscoelastic relaxation of shear stresses in the weak Maxwell viscosity asthenosphere. From experience with other postseismic studies, longer time series will allow us to develop more robust models of postseismic deformation and models of interseismic frictional coupling on the subduction interface. The complete 8-year-long data set is required to address fundamental problems: How much of the strain built up from subduction of the Pacific plate beneath the North American plate (the Sea of Okhotsk) has been released in the 2006 and 2007 Kuril earthquakes coseismically and postseismically? Is it possible to explain postseismic surface deformation at the Kuril subduction zone with the linear viscous mantle or a stress-dependent rheology is required? These problems are especially important after the giant 2011 Mw 9.0 Tohoku earthquake, which made the scientists question the validity of conventional precursors of large earthquakes: location of seismic gaps and location of asperities (patches of high frictional locking at a subduction interface).