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

合作研究：大地震后震后 GPS 观测的千岛堪察加俯冲带软流圈流变学

• 批准号: 1546998
• 负责人: Mikhail Kogan
• 金额: $ 18.5万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-06-15 至 2017-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1546998&HistoricalAwards=false
• 关键词: Collaborative; Research; Rheology; asthenosphere; Kuril

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.

该项目涉及西北太平洋千岛俯冲带区域，该区域经常发生灾难性地震。在2006-2007年间，一对8兆瓦的大地震部分打破了俯冲带地震活动中最明显的空白之一。该项目的一个直接重点是获取跨越2007-2016年时间段的震后GPS测量。这些数据将使科学家能够更好地了解长期地震周期，并将对了解这里和其他类似环境中的地震危险非常重要。该项目将继续并加强美国大学和俄罗斯科学院机构之间的合作。该项目提供的数据将可供广大科学界使用。需要完整的10年数据集来解决根本问题：在2006年和2007年千岛地震中，由于太平洋板块俯冲到北美板块(鄂霍次克海)之下而形成的应变中，有多少是在同震和震后释放的？是否有可能用线性粘性地幔来解释千岛-堪察加俯冲带的震后地表变形，或者是否需要依赖应力的流变学？这些问题在2011年日本东北9.0兆瓦大地震后变得尤为重要，这场地震让科学家们质疑即将发生的大地震前兆的有效性：地震空隙(地震活动的空间空隙)的位置和凹凸体的位置(俯冲界面上的高摩擦锁定斑块)。对这种长度的震后形变的观测是罕见的，可以极大地提高对地幔流变性的了解。粘弹性松弛三维模拟的初步结果现在包括板块几何形状对线性和非线性地幔流变学的影响，重点是匹配五年及以后观测到的台站速度。拟议的工作将基于显著增加的数据间隔(延长20%)来扩展建模工作。这一相对较晚的阶段数据对于检验非线性流变学的假说至关重要。