Abstract The crustal structure of the overriding plate in a subduction zone can have significant effects on subduction processes and therefore hazard along the margin. To investigate the controls of the overriding North American crust on the Cascadia Subduction Zone, a dense, trench perpendicular line of nodal seismometers was deployed in the Central Oregon forearc. The location of this deployment was chosen to fulfill two main goals (1) to examine the utility of large-N, short duration, nodal deployments in passive source seismic imaging (2) and to gain a better understanding of the structure of the Central Oregon forearc. With ∼40 days of continuous data recorded on 174, 3-component, 5 Hz instruments in a 130 km line with 500 m station spacing, 116 earthquakes and explosions are detected and located, a ∼3.5-fold increase from the number reported by the regional Pacific Northwest Seismic Network (PNSN) catalog. P, S, and PmP travel times from earthquakes located near the line of stations are used in a local earthquake tomography study to model Vp/Vs in the upper/middle crust and Vp throughout the crust of central Oregon down to 40 km depth. In conjunction, these models show a clear compositional discontinuity between the upper and lower Siletzia Terrane at ∼10 km depth as well as a zone of low Vp (6.5–6.8 km/s) in the lower crust that is attributed to slab derived fluids. This region of low Vp is juxtaposed with high Vp (6.9–7.2 km/s) to the east, interpreted as a strong, unfractured, block of Siletzia. High pore fluid pressures in the lower crust have been imaged to varying degrees across the Cascadia subduction zone. These features may be related to both the occurrence of tremor near the plate interface and the reduction of upper plate crustal earthquakes.

中文翻译：

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使用大 N、短持续时间、节点阵列对俄勒冈中部前弧进行局部地震断层扫描

摘要 俯冲带上覆板块的地壳结构对俯冲过程有显着影响，从而对边缘产生危害。为了研究卡斯卡迪亚俯冲带上覆盖的北美地壳的控制，在俄勒冈州中部前弧部署了一条密集的沟渠垂直线节点地震仪。选择此部署的位置是为了实现两个主要目标 (1) 以检查大 N、短持续时间、节点部署在被动震源地震成像中的效用 (2) 并更好地了解俄勒冈州中部的结构前弧。在 130 公里长、站距为 500 米的线路上，用 174 台 3 分量、5 Hz 仪器记录了大约 40 天的连续数据，检测并定位了 116 次地震和爆炸，大约 3. 比区域太平洋西北地震台网 (PNSN) 目录报告的数量增加了 5 倍。来自台站线附近地震的 P、S 和 PmP 旅行时间用于局部地震层析成像研究，以模拟上/中地壳中的 Vp/Vs 和整个俄勒冈州中部地壳中深达 40 公里深度的 Vp。结合起来，这些模型显示了大约 10 公里深度的上部和下部 Siletzia 地体之间的明显成分不连续性以及下地壳中的低 Vp（6.5-6.8 公里/秒）区域，这归因于板片衍生的流体。这个低 Vp 的区域与东部的高 Vp（6.9-7.2 公里/秒）并列，被解释为一个坚固的、未断裂的 Siletzia 块。下地壳的高孔隙流体压力已在卡斯卡迪亚俯冲带上不同程度地成像。