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

众所周知，卡斯卡迪亚俯冲带很少(每隔500年)发生一次地震，但可能会发生非常大的地震(最高可达9级)。最近一次这样的地震发生在1700年1月26日，过去20年获得的GPS数据表明，俯冲带断层上的应变正在积累，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，仍存在相当大的不确定性。不同的地震情景会导致不同的地面震动预测，进而影响建筑规范和应急预案。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。其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段的因素以及由此导致的人口聚居区和沉积盆地的地面震动幅度。该项目占地面积大，有许多实地工作人员参与，将为学生提供研究经验，并为太平洋西北地区的公共宣传和地质灾害教育提供机会。该项目是俄勒冈州立大学、俄勒冈大学、尤金、南达科他州矿业与技术学院和美国地质调查局的合作项目。该项目的最终目标是生成一个高分辨率的活动俯冲系统模型，该模型将跨越卡斯卡迪亚板块边界，包括主要沿走向分段之间的过渡，并跨越从名义上锁定的区域向下倾斜到深度的过渡，在那里，板块运动通过幕间地震和滑动来适应。太平洋西北海岸临时短周期地震仪的密集网络将把上覆板块和下行板块的结构以及板块界面带内物质的厚度和特征的高分辨率成像扩展到对理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长线以1公里的间隔单一部署三分量仪器，这些倾斜线嵌入间隔7-10公里的稀疏地震仪网格中，总共有约700个三分量地震台。为了将板块边界孕震部分的结果与更大规模的弧前和弧前结构联系起来，将有两条剖面延伸到弧前。在部署期间，所有站点都将记录自然来源和人工来源。这项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，对于约束地震噪声、大地电磁和势场数据的分析，以及改进对太平洋西北部地震地面震动和海啸产生的预测至关重要。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.