EAR-PF: A Multiscale Seismic Velocity Model for the Gulf of Alaska

Evans Onyango被授予NSF EAR博士后奖学金，以开展与开发阿拉斯加湾多尺度地震速度模型有关的研究和教育活动。这项工作将在卡尔·塔普博士的指导下在阿拉斯加费尔班克斯大学进行。地球表面被分割成不断运动的板块，这些板块沿着板块之间的边界相互碰撞、滑动或拉开。板块间的相互作用造就了山脉，引发了火山活动，并产生了大地震。阿拉斯加是世界上地震最活跃的板块边界之一，1964年发生了9.2级地震，这是美国有记录以来最大的地震。科学家依靠地球地下物质的三维模型来了解板块构造过程并评估地质灾害。为了更好地了解大地震，科学家必须了解地震波如何与地球地下物质相互作用。对阿拉斯加南部地震波场进行建模的一个主要限制是缺乏三维近海模型。永久地震台站位于陆地上，远离海上地震，这使得对沿海城市的地面运动进行建模变得困难。该项目旨在建立和测试阿拉斯加湾的三维地下模型，以更好地了解沿海地区复杂的地震地面运动。其目标是通过结合以前研究中现有的二维模型来创建一个全面的三维模型。将对该模型中的地震波传播进行计算机模拟，以生成预测的地震图，并将其与该地区中等地震的记录地震图进行比较。最终的模型将通过IRIS地球模型协作公开访问，IRIS地球模型协作是地球模型的公共存储库。该项目将涉及到容易发生地震和海啸危险的当地沿海社区。位于构造活跃边缘的近海地区，如阿拉斯加南部或加利福尼亚州南部，往往表现出极端的结构复杂性，并在震级和机制方面产生广泛的地震。在阿拉斯加南部，雅库塔特微板块在北美板块下方的活动碰撞和吸积，以及该活动俯冲带上的增生楔体的结构，都是导致该地区复杂结构的因素之一。在陆地上小规模和大规模地部署地震仪器，如EarthScope可移动阵列，已经产生了许多阿拉斯加大陆的层析模型，其中大多数包括固有的平滑，无法捕捉到近海环境的尖锐界面。相比之下，在20世纪80年代至21世纪头10年间，阿拉斯加湾近海地区只有少数几个源自海洋研究的高分辨率2D速度模型。该项目建议利用这些来自阿拉斯加湾的现有图像来创建一个全面的3D速度模型，该模型将具有许多用途，如模拟地震波场、了解活动构造和模拟俯冲系统的地球动力学。由合成的3D模型计算的合成波形将与研究区中大地震记录的地震图进行比较，以验证模型的有效性。地震记录失配值也将与其他可用层析模型的性能进行比较。该项目将开发阿拉斯加湾的3D速度模型，该模型将通过IRIS地球模型协作公开访问，IRIS地球模型协作是地球模型的公共存储库。该项目由地球科学博士后奖学金计划和既定的激励竞争研究计划(EPSCoR)共同资助。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。

Evans Onyango has been awarded an NSF EAR Postdoctoral Fellowship to conduct research and education activities related to developing a multiscale seismic velocity model for the Gulf of Alaska. This work will take place at the University of Alaska Fairbanks under the mentorship of Dr. Carl Tape. The surface of the Earth is divided into plates that are in constant motion and collide, slide past, or pull away from each other along the boundaries between plates. Plate interactions build mountains, cause volcanic activity, and produce large earthquakes. Alaska hosts one of the world’s most seismically active plate boundaries, which produced the 1964 magnitude 9.2 earthquake, the largest ever recorded in the United States. Scientists rely on three-dimensional models of Earth’s subsurface material to understand plate tectonic processes and to assess geologic hazards. In order to better understand large earthquakes, scientists must understand how seismic waves interact with Earth’s subsurface materials. A primary limitation to modeling the seismic wavefield in southern Alaska is the lack of a three-dimensional offshore model. Permanent seismic stations are on land, far from offshore earthquakes, which makes it difficult to model ground motion at coastal cities. This project seeks to build and test a three-dimensional subsurface model for the Gulf of Alaska to better understand the complex earthquake ground motion in coastal regions. The goal is to create a comprehensive three-dimensional model by combining existing two-dimensional models from previous studies. Computer simulations of seismic wave propagation within this model will be performed to generate predicted seismograms that will be compared with recorded seismograms from moderate earthquakes in the region. The final model will be publicly accessible via the IRIS Earth Model Collaboration, a public repository for Earth models. The project will involve outreach to local coastal communities prone to seismic and tsunami hazards.Offshore regions at tectonically active margins, such as southern Alaska or southern California, often exhibit extreme structural complexity and produce a wide range of earthquakes in terms of magnitudes and mechanisms. In southern Alaska, the active collision and accretion of the Yakutat microplate beneath the North America plate and the structure of the accretionary wedge at this active subduction zone are examples of factors contributing to the complex structure of the region. Small-scale and large-scale deployments of seismic instruments on land such as the EarthScope Transportable Array have yielded numerous tomographic models of the mainland Alaska, most of which include inherent smoothing that cannot capture the sharp interfaces of the offshore setting. By comparison, the offshore region of the Gulf of Alaska has only been studied with a sparse assortment of high-resolution 2D velocity models derived from marine studies between the 1980s and 2000s. This project proposes leveraging these existing images from the Gulf of Alaska to create a comprehensive 3D velocity model that will have many uses such as modeling the seismic wavefield, understanding active tectonics, and modeling geodynamics of the subduction system. Synthetic waveforms calculated from the resultant 3D model will be compared with seismograms recorded from moderate and large earthquakes in the study area to validate the model. Seismogram misfit values will also be compared with the performance of other available tomographic models. This project will develop a 3D velocity model for the Gulf of Alaska that will be publicly accessible via the IRIS Earth Model Collaboration, a public repository for Earth models.This project is jointly funded by the Earth Sciences Postdoctoral Fellowship program and the Established Program to Stimulate Competitive Research (EPSCoR).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.