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: 1347343
• 负责人: Demian Saffer
• 金额: $ 17.99万
• 依托单位: Pennsylvania State Univ University Park
• 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 2018-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1347343&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、最具破坏性的地震和海啸是沿着俯冲巨型逆冲层产生的。 这些板块构造边界断层在地震中破裂的部分被称为震源带。 最近对传播到近地表的高滑移的观测，以及异常慢滑移事件的新发现，对解释地震带行为的广泛持有的假设提出了基本问题。 特别是，许多俯冲断层的发震带似乎是“斑驳的”，一些区域在大地震中突然断裂，而另一些区域则通过稳定的抗震蠕变而滑动。此外，在某些深度范围内，通常是在发震带的浅部和深部边缘，在许多边缘都观察到了具有异常低频能量的慢滑事件和地震。目前对导致这些不同滑动模式的断层带条件和过程的了解是有限的，很大程度上是因为对地下原位条件的定量约束很少。 因此，相关的地震和海啸灾害同样受到了很差的限制。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相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俯冲巨型逆冲断层沿线的原位孔隙流体压力和应力。最终，通过对从海沟到发震带的板块边界沿线的地下条件进行定量估计，本研究将测试各种地震行为的假设机制。为了实现这一目标，该研究将整合来自现代海洋沉积物和地震的实验室数据。利用现有的多分辨率地球物理数据挖掘出变泥岩，以提高我们对从海沟到约 30-40 公里深度的板块边界巨型逆冲层的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比和高反射率感知到的俯冲巨型逆冲断层沿线的原位条件、材料和特性是什么？在接近静压力和低有效应力的情况下，地震数据在多大程度上对弱变沉积物质与高孔隙度河道或斑块进行成像？ 2）板块边界的特性如何随深度和沿走向变化，以及它们与地震活动和上部板块变形有何关系？这两个首要问题将通过以下方式解决：(1) 从海沟至约 30-40 km 深度的主动和被动源数据集中提取对巨型逆冲断层地球物理特性的详细约束（Vp、Vp/Vs、反射率）； (2) 通过对阿拉斯加近海 IODP 岩心和科迪亚克岛断层带样本进行实验室实验，确定与阿拉斯加边缘原位俯冲界面相关的沉积物和岩石的弹性和水文特性； (3) 整合地球物理和实验室组成部分，以测试有关材料特性和状态变量对俯冲逆冲方向地球物理特征的作用的假设； (4)通过微震活动的精确重定位研究巨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、一套已收集的样本以及 DSDP/IODP 岩心和数据。总体而言，这项协调研究将极大地提高我们对巨型逆冲断层沿线的条件和物质及其与地震活动关系的理解，并作为其他边缘类似研究的模板。