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

卡斯卡迪亚俯冲带是已知的产生不频繁（每500年），但潜在的非常大（高达9级）地震。最近一次这样的地震发生在1700年1月26日，在过去二十年中获得的GPS数据表明，应变正在俯冲带断层上积累，为未来的地震做准备。然而，在卡斯卡迪亚地震期间，俯冲带的地质结构将如何影响应变释放存在相当大的不确定性。不同的地震情景会导致完全不同的预测地面震动，这反过来又会影响建筑规范和应急响应计划。该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，以便深入了解地震期间控制滑动分段的因素以及人口稠密地区和沉积盆地的地面震动幅度。凭借其庞大的足迹和许多领域的手参与，该项目将提供学生的研究经验和机会，为公众宣传和教育有关地质灾害在太平洋西北部。该项目是俄勒冈州州立大学、俄勒冈州大学、尤金、南达科他州矿业与技术学院和美国地质调查局之间的合作项目。该项目的最终目标是生成一个活动俯冲系统的高分辨率模型，该模型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，并穿过从名义上的锁定区向下倾斜到板块运动被幕式震颤和滑动所适应的深度的过渡。沿太平洋西北部海岸沿着建立的密集的临时短周期地震仪网络将扩大对上覆和下行板块结构的高分辨率成像，以及对板块交界带内物质的厚度和特性的高分辨率成像，直至对了解地震过程至关重要的深度。阵列设计包括沿倾斜线的陆上延伸部分以1 km的间隔沿着单次部署三分量仪器，倾斜线嵌入间隔7-10 km的地震仪稀疏网格内，总共约有700个三分量地震台站。为了将板块边界孕震部分的结果与更大规模的前弧和弧结构联系起来，两个剖面将延伸穿过前弧。在部署期间，所有监测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模型也将可以访问，对于限制地震噪声、大地电磁和势场数据的分析至关重要，该奖项反映了NSF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进行评估，被认为值得支持的搜索.

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.