A shallow sub-seafloor seismic model that includes well-determined seismic velocities and clarifies sediment-crust discontinuities is needed to characterize the physical properties of marine sediments and the oceanic crust and to serve as a reference for deeper seismic modeling endeavors. This study estimates the seismic structure of marine sediments and the shallow oceanic crust of the Alaska-Aleutian subduction zone at the Alaska Peninsula, using data from the Alaska Amphibious Community Seismic Experiment (AACSE). We measure seafloor compliance and Ps converted wave delays from AACSE ocean-bottom seismometers (OBS) and seafloor pressure data and interpret these measurements using a joint Bayesian Monte Carlo inversion to produce a sub-seafloor S-wave velocity model beneath each available OBS station. The sediment thickness across the array varies considerably, ranging from about 50 m to 2.80 km, with the thickest sediment located in the continental slope. Lithological composition plays an important role in shaping the seismic properties of seafloor sediment. Deep-sea deposits on the incoming plate, which contain biogenic materials, tend to have reduced S-wave velocities, contrasting with the clay-rich sediments in the shallow continental shelf and continental slope. A difference in S-wave velocities is observed for upper oceanic crust formed at fast-rate (Shumagin) and intermediate-rate (Semidi) spreading centers. The reduced S-wave velocities in the Semidi crust may be caused by increased faulting and possible lithological variations, related to a previous period of intermediate-rate spreading.

中文翻译：

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沿阿拉斯加-阿留申俯冲带的阿拉斯加半岛海底地震结构特征


需要一个浅层海底地震模型，该模型包括明确确定的地震速度并阐明沉积物-地壳的不连续性，以表征海洋沉积物和海洋地壳的物理特性，并作为更深入的地震建模工作的参考。本研究使用阿拉斯加两栖社区地震实验 （AACSE） 的数据估计了阿拉斯加半岛阿拉斯加-阿留申俯冲带海洋沉积物的地震结构和浅海地壳。我们测量来自 AACSE 海底地震仪 （OBS） 和海底压力数据的海底顺应性和 Ps 转换波延迟，并使用联合贝叶斯蒙特卡洛反演来解释这些测量值，以在每个可用的 OBS 站下方生成海底下 S 波速度模型。整个阵列的沉积物厚度差异很大，从大约 50 m 到 2.80 km 不等，最厚的沉积物位于大陆斜坡。岩性成分在塑造海底沉积物的地震特性中起着重要作用。进入板块上的深海沉积物含有生物物质，往往具有降低的 S 波速度，与浅大陆架和大陆斜坡中富含粘土的沉积物形成鲜明对比。在快速速率 （Shumagin） 和中等速率 （Semidi） 扩散中心形成的上层洋壳中观察到 S 波速度的差异。Semidi 地壳中 S 波速度的降低可能是由断层增加和可能的岩性变化引起的，这与之前的中等速率扩张有关。