Impact of bending related faulting on the seismic properties of the incoming oceanic plate offshore of Nicaragua
Impact of bending related faulting on the seismic properties of the incoming oceanic plate offshore of Nicaragua
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DOI：
10.1029/2007jb005291
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发表时间：
2008-05-30
影响因子：
3.9
通讯作者：
McIntosh, Kirk
中科院分区：
文献类型：
--
作者：
Ivandic, Monika;Grevemeyer, Ingo;McIntosh, Kirk
[1] 在尼加拉瓜近海的中美洲海沟进行了地震广角和折射实验，以研究俯冲前与弯曲相关的正断层对海洋岩石圈地震特性的影响。根据多道地震反射（MCS）数据的反射率模式，表明与弯曲相关的断层作用促进了传入海洋岩石圈的水化和蛇纹石化。地震广角和折射数据是沿着一条横断面收集的，该横断面从尚未受俯冲影响的外隆起区域延伸到尼科亚半岛西北部的海沟，其中多波束测深数据显示临海海沟斜坡上有明显的正断层。地震折射和广角反射数据的层析成像联合反演在海沟轴向海的地壳和最上地幔中产生了异常低的地震 P 波速度。与正常成熟洋壳相比，地壳速度降低0.2-0.5 km s(-1)。最上地幔的地震速度为7.6-7.8 km s(-1)，比地幔橄榄岩的典型速度低5-7%。 P波速度从外隆起向海沟轴的这些系统变化表明俯冲板片的演化过程与海水通过断层和裂缝岩石圈的渗透以及地幔橄榄岩的蛇纹石化一致。如果水合作用确实影响了地幔的地震特性，那么在地幔最上层 3-4 公里处，蛇纹石化可能会达到 12-17%，这取决于未知的断裂程度及其对俯冲岩石圈弹性特性的影响。
[1] A seismic wide-angle and refraction experiment was conducted offshore of Nicaragua in the Middle American Trench to investigate the impact of bending-related normal faulting on the seismic properties of the oceanic lithosphere prior to subduction. On the basis of the reflectivity pattern of multichannel seismic reflection (MCS) data it has been suggested that bending-related faulting facilitates hydration and serpentinization of the incoming oceanic lithosphere. Seismic wide-angle and refraction data were collected along a transect which extends from the outer rise region not yet affected by subduction into the trench northwest of the Nicoya Peninsula, where multibeam bathymetric data show prominent normal faults on the seaward trench slope. A tomographic joint inversion of seismic refraction and wide-angle reflection data yield anomalously low seismic P wave velocities in the crust and uppermost mantle seaward of the trench axis. Crustal velocities are reduced by 0.2-0.5 km s(-1) compared to normal mature oceanic crust. Seismic velocities of the uppermost mantle are 7.6-7.8 km s(-1) and hence 5-7% lower than the typical velocity of mantle peridotite. These systematic changes in P wave velocity from the outer rise toward the trench axis indicate an evolutionary process in the subducting slab consistent with percolation of seawater through the faulted and fractured lithosphere and serpentinization of mantle peridotites. If hydration is indeed affecting the seismic properties of the mantle, serpentinization might be reaching 12-17% in the uppermost 3-4 km of the mantle, depending on the unknown degree of fracturing and its impact on the elastic properties of the subducting lithosphere.