Collaborative Research: Cascadia2020: Investigating subduction zone segmentation with a 3D high-resolution Vp model

众所周知，卡斯卡迪亚俯冲带产生的地震并不频繁（每~500年），但可能非常大（高达9级）。最近一次这样的地震发生在1700年1月26日，过去二十年中获得的GPS数据表明，在俯冲带断层上，应变正在积聚，为未来的地震做准备。然而，关于俯冲带的地质结构如何影响卡斯卡迪亚地震期间的应变释放，存在相当大的不确定性。不同的可能的地震情景导致不同的预测地面震动，这反过来影响建筑规范和应急响应计划。这个项目将对卡斯卡迪亚大地震发生地区的地壳结构进行成像。目的是了解地震速度的三维变化，以便深入了解控制地震期间滑动分割的因素以及在人口稠密地区和沉积盆地中产生的地面震动幅度。该项目占地面积大，有许多实地人员参与，将为学生提供研究经验，并为太平洋西北部地质灾害的公共宣传和教育提供机会。该项目由俄勒冈州立大学、俄勒冈大学尤金分校、南达科他州矿业与技术学院和美国地质调查局合作完成。该项目的最终目标是建立一个高分辨率的活动俯冲系统模型，该系统将跨越卡斯卡迪亚板块边界，包括主要沿走向段之间的过渡，并跨越从名义上的锁定带向下倾斜到板块运动由间歇性震颤和滑动调节的深度的过渡。沿太平洋西北海岸建立一个密集的临时短周期地震仪网络，将把对上覆和下行板块结构的高分辨率成像，以及板块界面带内物质的厚度和特征，扩展到对理解地震过程至关重要的深度。该阵列设计包括沿倾斜线的陆上延伸每隔1公里部署三分量仪器，这些倾斜线嵌入在相隔7-10公里的地震检波器网格中，总共有大约700个三分量地震站。为了将板块边界发震部分的结果与更大规模的前弧和弧结构联系起来，将在前弧上延伸两条剖面。在部署期间，所有台站都将记录自然源和人为源。这次实验的地震数据将立即提供给社区。由此产生的高分辨率3D Vp模型也将可供使用，对于地震噪声、大地电磁和势场数据的约束分析以及改善太平洋西北地区地震地面震动和海啸产生的预测至关重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Cascadia subduction zone is known to generate infrequent (every ~500 years) but potentially very large (up to magnitude 9) earthquakes. The most recent such earthquake occurred on January 26th, 1700, and GPS data acquired during the last two decades suggest that strain is accumulating across the subduction zone fault in preparation for a future earthquake. However, there is considerable uncertainty about how the geologic structure of the subduction zone will impact strain release during a Cascadia earthquake. Different plausible earthquake scenarios result in quite different predicted ground shaking, which in turn influences building codes and emergency response plans. This project will image the structure of the crust in the region where large Cascadia earthquakes are thought to occur. The objective is to understand three-dimensional variations in seismic velocity in order to provide insights into the factors that control segmentation of slip during earthquakes and the resulting amplitude of ground shaking in populated areas and sedimentary basins. With its large footprint and involvement of many field hands, this project will provide student research experiences and opportunities for public outreach and education about geohazards in the Pacific Northwest. This project is a collaboration between Oregon State University, University of Oregon, Eugene, South Dakota School of Mines and Technology and the U.S. Geological Survey.This project has the ultimate goal of generating a high-resolution model of an active subduction system that will span the Cascadia plate boundary, including the transition between major along-strike segments, and cross the transition from the nominally locked zone down-dip to depths where plate motion is accommodated by episodic tremor and slip. A dense network of temporary short-period seismometers along the coast of the Pacific Northwest will extend high resolution imaging of the structure of the overlying and down-going plates, as well as the thickness and characteristics of material within the plate interface zone, to depths that are critical for understanding earthquake processes. The array design includes a single deployment of three-component instruments at 1-km intervals along the onshore extension of dip lines embedded within a sparser grid of seismometers spaced 7-10 km apart for a total of ~700 three-component seismic stations. To tie results from the seismogenic part of the plate boundary to larger-scale forearc and arc structure, two profiles will extend across the forearc. All stations will record natural sources as well as man-made sources for the duration of the deployment. The seismic data from this experiment will be made immediately available to the community. The resulting high-resolution 3D Vp model will also be made accessible and is critical for constraining analyses of seismic noise, magnetotelluric and potential field data, as well as for improving predictions of earthquake ground shaking and tsunami generation in the Pacific Northwest.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.