Collaborative Research: A 3D Seismic Study of the Pacific-North American Plate Boundary in Southern California

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。知识价值：加利福尼亚南部的太平洋-北美板块边界是地质历史上记录的海洋扩张中心俯冲的唯一例子之一，但这一过程很可能是地球历史的一个共同组成部分。南加州的太平洋-北美板块边界几乎有一半位于近海，但人们对海洋板块的物理特性、变形方式或对北美西部的影响知之甚少。该项目将在横跨太平洋-北美板块边界的南加州海岸进行被动地震实验，部署24台长时间宽带海底地震仪（OBS）。OBS数据将与加州永久综合地震台网记录的同事件数据相结合，覆盖陆上盆地、圣安德烈亚斯断层和北美板块。目的是通过识别太平洋板块和近岸微板块的物理性质和变形风格，了解这一边界的构造相互作用，并区分对比的上地幔地球动力学情景，预测北美西部地下大规模的地幔流动模式。地震研究的目的是描述裂谷系统、破碎的俯冲板块、圣安德烈亚斯转换断层系统的延长和块体旋转之间碰撞的驱动板块运动的后果。特别重要的是了解影响弹性地壳应力状态以产生地震的力和流变学的来源。地震阵的边界重叠在太平洋板块的复杂破碎和断裂的近岸地区，在那里观察到几个微板块，并向西延伸，以提供与未断裂并以均匀速率形成的海洋岩石圈的比较。研究结果将有助于理解板块相对运动的边界力、海洋和大陆尺度形变的驱动力和特征，以及近海构造对大陆边缘增生过程的影响。另一个目标是检查当地地震数据及其震源机制的地震活动模式。拟议的OBS网络记录的当地地震活动预计将产生更准确的海上震源目录，可用于识别背景地震活动与绘制的海上断层之间的空间关系。更广泛的影响：更广泛的影响将通过与南加州海洋研究所合作开展的活动来实现，包括创造实践科学机会和教育材料。这些材料将把海底地震仪的数据和一般的近海地震学纳入高中和大学学生的课程中。本科生和研究生将参与研究巡游、科学分析和相关教学活动。加州州立大学北岭分校是一所指定的少数族裔服务机构，该校的硕士和本科生将通过Catalyst项目招收女性和少数族裔学生，该项目积极招收地质学和地球物理学的少数族裔学生。实验数据将在IRIS数据管理中心和南加州地震数据中心存档，这两个中心都是多用户数据存档设施，对其他科学家、学生和非科学家的数据请求开放。本实验的局部地震数据收集部分将在可直接造福社会的应用中增强对危险海上地震结构的理解。海上背景地震活动性目录将阐明海上断层的活动性。当地地震相位数据将有助于建立一个更新的三维地壳地震速度模型，该模型扩展到近海，供研究人员用于进行三维波传播模拟，以估计震动对附近沿海社区的影响，以便在减灾工作中使用。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Intellectual Merit: The Pacific-North America plate boundary in southern California is one of the only examples of recorded subduction of an oceanic spreading center in geological history, but this process is likely to be a common component of Earth history. Almost half of the Pacific-North America plate boundary in southern California lies offshore, but little is known about the physical properties of the oceanic plate, its mode of deformation, or its influence on western North America. This project will deploy 24 long-duration, broadband Ocean Bottom Seismometers (OBS) in a passive seismic experiment off the coast of southern California that spans the oceanic half of the Pacific-North America plate boundary. The OBS data will be combined with same-event data recorded on the permanent California Integrated Seismic Network for coverage across the onshore basins, San Andreas fault, and into the North America plate. The objective is to understand the tectonic interaction at this boundary by identifying the physical properties and deformation styles of the Pacific plate and near-shore microplates, as well as distinguish among contrasting upper mantle geodynamic scenarios which predict large-scale mantle flow patterns beneath western North America. The seismic studies aim to characterize the driving plate motion consequences of collision between the rift system, a fragmented subducted plate, the lengthening of the San Andreas transform fault system, and block rotations. Of particular relevance is understanding the source of the forces and rheology that affect the stress state of the elastic crust to generate earthquakes. The boundaries for the seismic array overlap the region of complex breakup and fracture of the Pacific plate near-shore where several microplates are observed, and extends far to the west to provide comparison with oceanic lithosphere that is not fractured and has formed at a uniform rate. The results will aid in understanding the boundary forces due to relative plate motions, the driving forces and characteristics of oceanic and continental scale deformation, and how the continental margin accretionary process is influenced by offshore tectonics. An additional goal is to examine the local earthquake data and their focal mechanisms for seismicity patterns. The local seismicity recorded by the proposed OBS network is expected to produce a more accurate offshore hypocenter catalog that can be used to identify spatial relationships between background seismic activity with mapped offshore faultsBroader Impacts: The broader impacts will be carried out through activities that include a partnership with the Southern California Marine Institute to create hands-on scientific opportunities and educational materials. These materials will incorporate the OBS data and general offshore seismology into programs for high school and college students. Undergraduate and graduate students will participate in the research cruises, scientific analysis, and related teaching activities. Masters and undergraduate level students from Cal State Northridge, a designated Minority Serving Institution, will include women and minority students through the Catalyst program which recruits actively for minorities in geology and geophysics. Data from the experiment will be archived at the IRIS Data Management Center and the Southern California Earthquake Data Center, both of which are multi-user data archival facilities that are open to data requests from other scientists, students, and non-scientists. The local earthquake data collection portion of this experiment will enhance the understanding of hazardous offshore seismic structures in applications that can directly benefit society. The offshore background seismicity catalog will elucidate the activity of offshore faults. Local earthquake phase data will contribute to an updated 3D crustal seismic velocity model that extends offshore to be used by researchers to carry out 3D wave propagation simulations to estimate the amount and effects of shaking on nearby coastal communities for use in mitigation efforts.