Collaborative Research: Probing the frictional behavior of the Tohoku megathrust using GPS, seismicity, and physics-based models

合作研究：利用 GPS、地震活动和基于物理的模型探索东北巨型逆冲断层的摩擦行为

• 批准号: 1620507
• 负责人: Kaj Johnson
• 金额: $ 16.15万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1620507&HistoricalAwards=false
• 关键词: Collaborative; Research; Probing; frictional; behavior

The largest earthquakes in the world occur in subduction zones, such as the Cascadia Subduction Zone in the northwestern US, where oceanic plates dive into Earth's mantle. The devastating magnitude 9, 2011 Tohoku-oki earthquake in northern Japan is a notable example, and by far the best instrumented giant earthquake in history. The data from this quake presents a unique opportunity to understand what controls the frequency and size of subduction zone earthquakes. Prior to 2011 it was known that the northern Japan subduction zone exhibited both slow sliding (fault creep without earthquakes) which relaxes stress, as well as rapid slip in earthquakes. It had been, erroneously, thought that the creeping zones would limit the area that could slip in large earthquakes such that magnitude 9 events were not possible. The researchers past work has shown that, contrary to expectation, the same part of the fault can exhibit both creep and earthquakes. This new project develops a rigorous physics-based understanding of the mechanical properties that control how and when fault creep occurs. Models will be tested against precise GPS measurements, which quantify how rapidly stress builds up, as well as small earthquakes which track fault creep. Previous analysis of GPS data recorded in Japan showed that fault creep accelerated in the decades leading up to the magnitude 9; remarkably this was confirmed by independent data from small repeating earthquakes. We will test the hypothesis that creeping areas expand with time as stress builds up on the plate boundary. P.I. Segall will participate in the Geoscape Bay Area Professional Development program for middle and high school science teachers. He will develop a module to translate science from the Tohoku earthquake in Japan to earthquake hazards in the U.S., which has particular relevance to the Cascade subduction zone. This project explores models to explain unique interseismic and post-seismic observations from northeast Japan, constrained by repeating earthquakes and GPS data, both before and after the 2011 Mw 9 earthquake. Our hypothesis for accelerating interseismic creep as well as afterslip overlapping historical ruptures is that while earthquakes nucleate in velocity weakening regions, they rupture into velocity strengthening regions due to strong dynamic weakening. In the interseismic period, creep penetrates into velocity strengthening zones, eroding locked asperities with time. The simulations include rate-state friction and thermal pressurization, and test predictions against GPS and repeating-earthquake data. Time dependent asperity erosion appears to be a promising mechanism to explain the long-duration strain transient. Elastic models with locked asperities restricted to seismogenic depths cannot explain coastal subsidence documented over the last century; these data require either deep coupling (60? 100 km) or mantle relaxation. GPS and seafloor geodetic measurements, post-Mw 9, require some combination of afterslip and deep mantle flow. The Tohoku coast underwent Holocene uplift, yet at present it is unknown whether postseismic processes alone will even recover the observed inter- and co-seismic subsidence. We will use coupled viscoelastic and physics-based afterslip models to examine relative contributions of mantle flow and interface coupling to interseismic deformation and further test the eroding asperity hypothesis. These physics-based models of fault friction and earthquake-cycle deformation are able to integrate diverse datasets and provide a comprehensive model of the mechanical behavior of this unique plate boundary. This project mentors a SURGE (Summer Undergraduate Research in Geoscience and Engineering) student to analyze GPS vertical time series from Tohoku and use these results to constrain interseismic slip rate on the plate boundary. The student will participate in workshops on preparing for the GRE, applying to graduate school, and understanding geoscience careers.

世界上最大的地震发生在俯冲带，例如美国西北部的卡斯卡迪亚俯冲带，海洋板在那里潜入地球的地幔。 日本北部的毁灭性幅度9，2011年的Toohoku-Oki地震是一个著名的例子，也是迄今为止历史上最好的巨型地震。 来自这种地震的数据提供了一个独特的机会，可以了解俯冲带地震的频率和大小是什么。 在2011年之前，众所周知，北部日本俯冲带表现出缓慢的滑动（没有地震的故障蠕变），这会放松压力，并在地震中快速滑动。 错误地认为，爬行的区域将限制可能在大地震中滑落的区域，因此无法实现9级事件。研究人员过去的工作表明，与期望相反，断层的同一部分可以表现出蠕变和地震。 这个新项目基于严格的物理学了解了控制故障蠕变的方式和何时发生的机械性能。 模型将针对精确的GPS测量进行测试，该测量量化了压力的迅速累积，以及跟踪断层蠕变的小地震。 对日本记录的GPS数据的先前分析表明，在幅度9级的几十年中，故障蠕变加速了。值得注意的是，这是通过小型重复地震的独立数据证实的。 我们将测试以下假设：随着压力在板边界上累积，蠕变区域会随着时间而扩展。 P.I. Segall将参加中学和高中科学老师的Geoscape Bay地区专业发展计划。他将开发一个模块，将科学从日本的Tohoku地震转化为美国的地震危害，该危害与级联俯冲区特别相关。该项目探索了解释日本东北部独特的经济震荡和地震后观察的模型，并在2011年MW 9地震之前和之后重复地震和GPS数据限制。我们的假设是加速跨度蠕变以及滑坡后重叠的历史破裂的假设是，尽管速度弱化区域中的地震降低了区域，但由于强烈的动态弱化，它们破裂成速度加强区域。在经济势时期，蠕变渗透到速度加强区域，随着时间的流逝侵蚀了锁定的锁定区域。这些模拟包括速率摩擦和热加压，以及针对GPS和重复进行电子数据的测试预测。时间依赖性的沙子侵蚀似乎是解释长期应变瞬变的有前途的机制。锁定的弹性模型仅限于地震深度，无法解释上个世纪记录的沿海沉降。这些数据需要深耦合（60？100 km）或地幔松弛。 GPS和海底大地测量，MW 9后需要将后置和深地幔流的组合组合。 Tohoku沿岸进行了全新世的提升，但目前尚不清楚单独的后期过程是否会恢复所观察到的跨性别和共同性的沉降。我们将使用耦合的粘弹性和基于物理学的后水样模型来检查地幔流量和界面耦合对间测变形的相对贡献，并进一步检验侵蚀的息肉假设。这些基于物理的故障摩擦和地震周期变形的模型能够整合各种数据集，并提供了该独特板边界的机械行为的全面模型。该项目指导了一项激增（地球科学和工程学的夏季本科研究）学生，分析了Tohoku的GPS垂直时间序列，并使用这些结果来限制板界对板丝的震动速率。学生将参加为GRE做准备，申请研究生院并了解地球科学职业的研讨会。