Along-Trench Structural Variations of the Subducting Juan de Fuca Plate From Multichannel Seismic Reflection Imaging
Along-Trench Structural Variations of the Subducting Juan de Fuca Plate From Multichannel Seismic Reflection Imaging
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DOI：
10.1002/2017jb015059
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发表时间：
2018-04-01
影响因子：
3.9
通讯作者：
Carton, Helene
中科院分区：
文献类型：
--
作者：
Han, Shuoshuo;Carbotte, Suzanne M.;Carton, Helene
为了描述Juan de Fuca（JdF）板块进入卡斯卡迪亚俯冲带时沿走向的构造变化，我们提供了JdF板块沿沿着400 km长的海沟平行断面（从北纬44.3度延伸至北纬47.8度）的叠前时间偏移多道地震反射图像。在1.8-3.0公里厚的沉积物覆盖层之下，我们的数据显示，基底地形异常与1.2公里高的海山和传播尾流（390-540米浮雕）附近有关。弱的莫霍面反射成像的传播尾迹下方，并符合减少Vp在下地壳和/或上地幔。下行板块中传播子尾流的推断位置与某些幕式地震和滑动事件的边界重合。我们建议，与这些功能相关的结构和水化的不均匀性可能会导致异常的板块界面特性，并有助于幕式震颤和滑动分割。与俯冲弯曲正断层一致的壳内反射具有明显倾角（20度-30度），在北纬45.8度附近发生变化，从局限于北部中地壳的北倾反射到穿过南部地壳的反向反射，与下地壳的Vp降低一致。这些观测结果表明，北纬45.8度以南的JdF板块发生了更广泛的断层变形和相关的水化作用，这可能是由于北纬46度板块倾角和俯冲阻力的变化造成的。基底偏移和莫霍面反射的突然深度/振幅变化的四个主要WNW走向的走滑断层下，穿过卡斯卡迪亚变形前成像，提供了强有力的证据，这些故障的较低的板块起源。
To characterize the along-strike structural variations of the Juan de Fuca (JdF) Plate as it enters the Cascadia subduction zone, we present prestack time migrated multichannel seismic reflection images of the JdF Plate along a 400-km-long trench-parallel transect extending from 44.3 degrees N to 47.8 degrees N. Beneath the 1.8-3.0-km-thick sediment cover, our data reveal basement topographic anomalies associated with a 1.2-km-high seamount and in the vicinity of propagator wakes (390-540-m relief). Weak Moho reflections are imaged beneath the propagator wakes and coincide with reduced Vp in the lower crust and/or uppermost mantle. The inferred locations of propagator wakes in the downgoing plate collocate with some of the boundaries of episodic tremor and slip events. We propose that the structural and hydration heterogeneities associated with these features could lead to anomalous plate interface properties and contribute to episodic tremor and slip segmentation. Intracrustal reflections with apparent dips (20 degrees-30 degrees) consistent with subduction bending normal faults change near 45.8 degrees N, from northward dipping reflections confined to the middle crust in the north to antithetic reflections through the crust in the south, coinciding with a Vp reduction in the lower crust. These observations indicate more extensive faulting deformation and associated hydration of the JdF Plate south of 45.8 degrees N, which likely results from variations of slab dip and resistance to subduction across 46 degrees N. Basement offsets and abrupt depth/amplitude changes in Moho reflections are imaged beneath the four major WNW trending strike-slip faults that cross the Cascadia deformation front, providing strong evidence of a lower plate origin for these faults.