Collaborative Research: The Aleutian megathrust from trench to base of the seismogenic zone; integration and synthesis of laboratory, geophysical and geological data

合作研究：从海沟到地震带底部的阿留申巨型逆冲断层；

• 批准号: 1347312
• 负责人: Donna Shillington
• 金额: $ 25.22万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-02-01 至 2017-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1347312&HistoricalAwards=false
• 关键词: Collaborative; Research; Aleutian; megathrust; trench

Earth's largest and most destructive earthquakes and tsunamis are generated along subduction megathrusts. The portion of these plate tectonic boundary faults that ruptures in earthquakes is known as the siesmogenic zone. Recent observations of high slip that propagates to the near surface, and new discoveries of anomalously slow slip events, have raised fundamental questions about widely held hypotheses that explain seismogenic zone behavior. In particular, the seismogenic zone of many subduction faults appears to be 'patchy', with some regions that fail suddenly in large earthquakes and others that slide by stable, aseismic creep. Additionally, in certain depth ranges, typically at the shallow and deep fringes of the seismogenic zone, slow slip events and earthquakes with anomalous low frequency energy have been observed at many margins. Current knowledge of the fault zone conditions and processes that cause these different modes of slip is limited, largely because quantitative constraints on in situ conditions in the subsurface are scarce. As a result, the associated earthquake and tsunami hazards are similarly poorly constrained. This project will combine high quality regional geophysical studies from the Aleutian subduction margin with laboratory experimental measurements on relevant rock and sediment, to calibrate the geophysical data and quantify in situ pore fluid pressure and stress along the subduction megathrust. Ultimately by providing quantitative estimates of the subsurface conditions along the plate boundary from the trench through the seismogenic zone, this study will test hypothesized mechanisms for the wide range of earthquake behavior.To accomplish this, the study will integrate laboratory data from modern oceanic sediment and exhumed metapelites with existing, multi-resolutional geophysical data to improve our understanding of in situ conditions and processes along the plate boundary megathrust from the trench to ~30-40 km depth. The project will address the following questions: 1) What are the in situ conditions, materials, and properties along the subduction megathrust that are sensed by low Vp, high Vp/Vs ratio, and high reflectivity? To what extent do seismic data image weak metasedimentary material vs. high-porosity channels or patches at near-lithostatic pressure and low effective stress? 2) How do the properties of the plate boundary change with depth and along-strike, and how do they relate to seismicity and upper plate deformation? These two overarching questions will be addressed by: (1) extracting detailed constraints on geophysical properties of the megathrust (Vp, Vp/Vs, reflectivity) from active and passive source datasets from the trench to depths of ~30-40 km; (2) defining elastic and hydrologic properties of sediment and rock relevant to the in situ subduction interface at the Alaska margin, via lab experiments on IODP cores from offshore Alaska and samples from exhumed fault zones on Kodiak Island; (3) integrating the geophysical and laboratory components to test hypotheses about the roles of material properties and state variables on geophysical signatures along the subduction thrust; and (4) investigating the correlation of megathrust properties with earthquake locations via precise relocation of microseismicity. The work will leverage several existing high-quality geophysical datasets, a suite of already collected samples, and DSDP/IODP cores and data. As a whole, this coordinated study will vastly improve our understanding of the conditions and materials along the megathrust, their relationship to seismicity, and serve as a template for similar studies at other margins.

地球上最大和最具破坏性的地震和海啸都是沿着沿着俯冲巨型逆冲断层产生的。 这些板块构造边界断层在地震中破裂的部分被称为地震带。 最近观测到的传播到近地表的高滑动，以及新发现的异常缓慢的滑动事件，对解释孕震区行为的广泛持有的假设提出了根本性的问题。 特别是，许多俯冲断层的孕震区似乎是“斑块状”的，有些地区在大地震中突然断裂，而另一些地区则通过稳定的、不稳定的蠕变而滑动。此外，在某些深度范围内，特别是在孕震区的浅部和深部边缘，在许多边缘观察到慢滑动事件和具有异常低频能量的地震。目前的知识断层带的条件和过程，导致这些不同的模式的滑动是有限的，主要是因为在地下原位条件的定量约束是稀缺的。 因此，相关的地震和海啸灾害同样没有得到很好的控制。该项目将把阿留申俯冲边缘的高质量区域地球物理研究与有关岩石和沉积物的实验室实验测量相结合，以校准地球物理数据，并量化沿着俯冲巨型逆冲断层的原地孔隙流体压力和应力。最后，通过对从海沟到孕震区的板块边界沿着地下条件的定量估计，本研究将测试大范围地震行为的假设机制。为了实现这一目标，本研究将把现代海洋沉积物和挖出的变岩的实验室数据与现有的，多分辨率地球物理数据，以提高我们对从海沟到~30-40 km深度的板块边界巨型逆冲断层沿线沿着现场条件和过程的理解。 该项目将解决以下问题：1）低Vp、高Vp/Vs比和高反射率所感测的俯冲巨型逆冲断层沿着的原位条件、材料和性质是什么？在近岩石静压力和低有效应力条件下，地震数据在多大程度上反映了弱变沉积岩物质与高孔隙度通道或斑块的关系？2)板块边界的性质如何随深度和走向而变化，它们与地震活动和上板块变形有何关系？这两个首要问题将解决：（1）提取详细的地球物理性质的巨型逆冲断层的约束条件（Vp，Vp/Vs，反射率）来自海沟至~30-40 km深度的主动和被动源数据集;（2）确定与阿拉斯加陆缘原地俯冲界面有关的沉积物和岩石的弹性和水文性质，通过对阿拉斯加近海IODP岩心和科迪亚克岛挖掘断层带样品的实验室实验：（3）综合地球物理和实验室成分，以检验关于物质性质和状态变量对沿着俯冲逆冲带地球物理特征的作用的假设;（4）通过对微震活动的精确定位，研究大型逆冲断层性质与地震位置的相关性。 这项工作将利用几个现有的高质量地球物理数据集，一套已经收集的样本，以及DSDP/IODP核心和数据。总的来说，这项协调一致的研究将极大地提高我们对巨型逆冲断层沿着的条件和材料及其与地震活动性的关系的理解，并为其他边缘的类似研究提供模板。