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

西北太平洋上1200公里长的千岛岛巨型逆冲带是地球上地震最活跃的地区之一。这是最后一个完全没有被空间大地测量学方法探测过的主要俯冲带。在2006年?2007年，该地区的两次大地震部分破坏了俯冲带地震活动中最明显的一个间隙（2006年11月15日的8.3兆瓦冲断层事件和2007年1月13日的8.1兆瓦伸展断层事件）。2009年1月15日同一地区发生的7.4兆瓦逆冲大地震表明地震危险性增加。千岛岛GPS阵列是在2006？2007年美国和俄罗斯科学家合作的地震。阵列观测记录了千岛群岛大地震后的同震和震后地表变形。项目最后阶段的直接重点是获取2007年至2014年期间不可替代的瞬态地震后数据。该项目将继续美国大学和俄罗斯科学院机构之间的合作。千岛岛GPS阵列在2006年收集的数据？2011年，我们开发了同震滑动模型和震后机制模型。结果表明，大部分震后运动是由弱麦克斯韦黏性软流层中剪切应力的粘弹性松弛引起的。从其他地震后研究的经验来看，更长的时间序列将使我们能够开发出更可靠的地震后变形模型和俯冲界面上的地震间摩擦耦合模型。完整的8年数据集是解决基本问题所必需的：在2006年和2007年千岛群岛地震同震和震后释放了多少由太平洋板块俯冲到北美板块（鄂霍次克海）之下所形成的应变？是否有可能用线性粘性地幔或应力相关流变学来解释千岛岛俯冲带的地震后地表变形？这些问题在2011年日本东北9.0级大地震之后显得尤为重要。那次地震让科学家们对传统大地震前兆的有效性提出了质疑：地震间隙的位置和凸起的位置（俯冲界面处的高摩擦锁定块）。

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).