南阿拉斯加区域三维P波高分辨层析成像研究

doi:10.12196/j.issn.1000-3274.2025.01.004

摘要/Abstract

摘要： 本文利用国际地震中心(ISC)提供的2000—2016年阿拉斯加地震走时目录, 使用基于程函方程的地震层析成像方法, 对阿拉斯加南部地区的地下三维速度结构进行反演, 获得了该区域高精度的P波速度模型。结果显示, 研究区域内地壳结构具有强烈的非均匀性, 地壳中的低速异常与地表的沉积盆地等地质构造存在明显的相关性。在上地幔中存在明显的相对高速异常, 对应俯冲的太平洋板块。在相对高速异常的俯冲板块上层, 存在一个薄的低速异常层, 推测可能是俯冲进入北美板块内部的亚库塔特微板块。 2018年安克雷奇M_W7.1地震发生于该微板块的边界上, 其发生可能由俯冲板块之间的相对运动引起。在斯普尔火山下方存在显著的低速异常, 可能是由于板块俯冲过程中物质部分熔融和脱水作用, 释放的流体向上涌动, 形成了以强相对低速异常为特征的岩浆通道和岩浆房; 而里道特火山下方以高速异常为主, 代表着俯冲板块的高速异常不连续, 可能暗示板块的撕裂。板块在俯冲过程中脱水反应释放的流体上涌及高温半熔融物质沿着倾斜的通道向上运动, 为地表火山活动提供了物质和能量来源。

关键词: 阿拉斯加南部地区, 地震层析成像, 地壳速度结构, 俯冲板块

Abstract: Utilizing the seismic travel-time catalog of Alaska from 2000 to 2016 provided by the International Seismological Centre (ISC), this study employs eikonal equation-based seismic tomography to invert the three-dimensional velocity structure of the subsurface in southern Alaska, resulting in a high-resolution P-wave velocity model for the region. The results reveal strong heterogeneity in the crustal structure. The low-speed anomalies in the crust align well with geological structures such as surface sedimentary basins. Distinct high-velocity anomalies are observed in the upper mantle, corresponding to the subducting Pacific plate. Above this high-velocity anomaly, a thin layer of low-velocity anomalies is present, presumably the Yakutat microplate subducting into the North American plate. The 2018 M_W7.1 Anchorage earthquake occurred at the boundary of this microplate, possibly triggered by relative motions between the subducting plate and the overriding plate. Beneath Spur Volcano, significant low-velocity anomalies are evident, possibly indicating the formation of magma channels and magma chambers characterized by strong low-velocity anomalies, influenced by the upwelling of fluids released by partial melt and dehydration of material during plate subduction. Conversely, high-velocity anomalies dominate beneath Redoubt Volcano, and the high-velocity anomaly representing the subducting slab is discontinuous, possibly suggesting plate tearing. The fluids released by the dehydration of the subducting plate, as well as the upward movement of high-temperature, partially-molten material along inclined channels, provide the material and energy sources for surface volcanic activity.

Key words: Southern Alaska, Seismic tomography, Crustal velocity structure, Subducting slab

中图分类号:

P315.2

周艳杰, 曹天明, 张雅楠, 马啸, 石玉涛, 黄雪源. 南阿拉斯加区域三维P波高分辨层析成像研究[J]. 地震, 2025, 45(1): 47-62.

ZHOU Yan-jie, CAO Tian-ming, ZHANG Ya-nan, MA Xiao, SHI Yu-tao, HUANG Xue-yuan. High Resolution Tomographic Study on the 3-D P-wave Velocity Structures of the Southern Alaska Area[J]. EARTHQUAKE, 2025, 45(1): 47-62.

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