Collaborative Research: Rheology of asthenosphere in the Kuril-Kamchatka subduction zone from postseismic GPS observations after great earthquakes

该项目涉及西北太平洋千岛岛俯冲带的灾难性地震区域。2006-2007年，两次大地震（里氏8级）在一定程度上破坏了俯冲带地震活动中最明显的间隙之一。该项目的当务之急是获取2007-2016年地震后的GPS测量数据。这些数据将使科学家更好地了解长期地震周期，对了解这里和其他类似地区的地震危害也很重要。该项目将继续并加强美国大学与俄罗斯科学院机构之间的合作。该项目提供的数据将供广泛的科学界使用。完整的10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来解释千岛群岛-堪察加俯冲带的地震后地表变形，或者是否需要应力依赖的流变学？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，这次地震使科学家们质疑即将发生大地震前兆的有效性：地震间隙的位置（地震活动的空间间隙）和凸起的位置（俯冲界面处的高摩擦锁定斑块）。这种长度的震后形变观测是罕见的，可以显著提高对地幔流变学的认识。粘弹性松弛三维建模的初步结果现在包括板状几何对线性和非线性地幔流变的影响，重点是匹配5年及以后观测到的台站速度。建议的工作将基于显著增加的数据间隔（延长20%）扩展建模工作。这些相对较晚的数据对于检验非线性流变假说至关重要。

The project relates to the region of the Kuril subduction zone in the northwest Pacific Ocean subject to disastrous earthquakes. In 2006-2007, a doublet of great (MW 8) earthquakes partly ruptured one of the most conspicuous gaps in subduction-zone seismic activity. An immediate focus of this project is to acquire post-earthquake GPS measurement spanning the time period 2007-2016. These data will allow scientists to better understand the long-term earthquake cycle and will be important for understanding seismic hazards here and in other similar settings. This project will continue and strengthen collaboration between US universities and institutions of the Russian Academy of Sciences. The data provided by the project will be available for use by the broad scientific community. The complete 10-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-Kamchatka subduction zone with the linear viscous mantle or is a stress-dependent rheology required? These problems are especially important after the giant 2011 MW 9.0 Tohoku (Japan) earthquake, which made the scientists question the validity of precursors of imminent large earthquakes: location of seismic gaps (spatial gaps in seismic activity) and location of asperities (patches of high frictional locking at a subduction interface). Observations of postseismic deformation of this length are rare and can significantly improve understanding of the rheology of the mantle. Preliminary results of the 3-D modeling of viscoelastic relaxation now include the effect of slab geometry for linear and nonlinear mantle rheologies with a focus on matching station velocities observed five years and later. The proposed work will extend the modeling efforts based on a significantly increased interval of the data (20% longer). This relatively late stage data is critical in testing the hypothesis of non-linear rheology.