We develop a 3-D isotropic shear velocity model for the Alaska subduction zone using data from seafloor and land-based seismographs to investigate along-strike variations in structure. By applying ambient noise and teleseismic Helmholtz tomography, we derive Rayleigh wave group and phase velocity dispersion maps, then invert them for shear velocity structure using a Bayesian Monte Carlo algorithm. For land-based stations, we perform a joint inversion of receiver functions and dispersion curves. The forearc crust is relatively thick (35–42 km) and has reduced lower crustal velocities beneath the Kodiak and Semidi segments, which may promote higher seismic coupling. Bristol Bay Basin crust is relatively thin and has a high-velocity lower layer, suggesting a dense mafic lower crust emplaced by the rifting processes. The incoming plate shows low uppermost mantle velocities, indicating serpentinization. This hydration is more pronounced in the Shumagin segment, with greater velocity reduction extending to 18 ± 3 km depth, compared to the Semidi segment, showing smaller reductions extending to 14 ± 3 km depth. Our estimates of percent serpentinization from V_S reduction and V_P/V_S are larger than those determined using V_P reduction in prior studies, likely due to water in cracks affecting V_S more than V_P. Revised estimates of serpentinization show that more water subducts than previous studies, and that twice as much mantle water is subducted in the Shumagin segment compared to the Semidi segment. Together with estimates from other subduction zones, the results indicate a wide variation in subducted mantle water between different subduction segments.

中文翻译：

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根据两栖地震数据确定的阿拉斯加俯冲带结构和水化的沿走向变化

我们利用海底和陆基地震仪的数据开发了阿拉斯加俯冲带的 3D 各向同性剪切速度模型，以研究结构的沿走向变化。通过应用环境噪声和远震亥姆霍兹断层扫描，我们得出瑞利波群和相速度色散图，然后使用贝叶斯蒙特卡罗算法将它们反演为剪切速度结构。对于陆基站，我们对接收器函数和频散曲线进行联合反演。弧前地壳相对较厚（35-42 km），科迪亚克段和塞米迪段下方的地壳速度较低，这可能会促进更高的地震耦合。布里斯托尔湾盆地地壳相对较薄，并且具有高速下层，表明裂谷过程形成了致密的镁铁质下地壳。传入的板块显示出较低的上地幔速度，表明蛇纹石化。这种水合作用在 Shumagin 段更为明显，与 Semidi 段相比，速度降低幅度更大，延伸至 18 ± 3 km 深度，而 Semidi 段的速度降低幅度较小，延伸至 14 ± 3 km 深度。我们对 V _S还原和 V _P /V _S的蛇纹石化百分比的估计值大于先前研究中使用 V _P还原确定的值，这可能是由于裂缝中的水对 V _S的影响大于对 V _P的影响。蛇纹石化的修正估计表明，与之前的研究相比，俯冲的水量更多，而且与塞米迪段相比，舒马金段俯冲的地幔水量是塞米迪段的两倍。结合其他俯冲带的估计，结果表明不同俯冲段之间俯冲地幔水存在很大差异。