Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion
Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion
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DOI：
10.1093/gji/ggx415
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发表时间：
2018-01-01
影响因子：
2.8
通讯作者：
Cresswell, D.
中科院分区：
文献类型：
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作者：
Davy, R. G.;Morgan, J. V.;Cresswell, D.
大陆超伸展在深加利西亚边缘的岩浆贫乏裂谷的特点是一个复杂的模式的断层，薄大陆断块和蛇纹石化，与当地折返，地幔橄榄岩沿着S-反射，解释为拆离面。为了充分了解这些特征的演变，重要的是对结构进行地震成像，并尽可能以最高分辨率模拟速度结构。走时层析成像模型揭示了这个超扩展域的长波长速度结构，但往往不足以准确地匹配反射地震成像中观察到的短波长结构。在这里，我们演示了二维时域声波全波形反演（FWI）在深加利西亚边缘收集的深水地震数据中的应用，以获得大陆超伸展的高分辨率速度模型。我们已经使用了几个质量保证程序来评估速度模型，包括观测波形和模拟波形的比较、棋盘格测试、参数和反演策略的测试以及与偏移反射图像的比较。我们的最终模型表现出增加地下速度的分辨率，特别是在最西部的大陆断块观察到的改善，与速度场的明显旋转，以匹配陡峭的倾斜反射。在整个S反射层中，速度对比明显，S层下方速度较低，表明优先地幔蛇纹化。这项研究支持了这一假设，即正常的断层作用，以水合上地幔橄榄岩，观察到的地震速度的系统性下降，与增加蛇纹石化。我们的研究结果证实了将FWI方法应用于稀疏深水地壳数据集的可行性。
Continental hyperextension during magma-poor rifting at the Deep Galicia Margin is characterized by a complex pattern of faulting, thin continental fault blocks and the serpentinization, with local exhumation, of mantle peridotites along the S-reflector, interpreted as a detachment surface. In order to understand fully the evolution of these features, it is important to image seismically the structure and to model the velocity structure to the greatest resolution possible. Traveltime tomography models have revealed the long-wavelength velocity structure of this hyperextended domain, but are often insufficient to match accurately the short-wavelength structure observed in reflection seismic imaging. Here, we demonstrate the application of 2-D time-domain acoustic full-waveform inversion (FWI) to deep-water seismic data collected at the Deep Galicia Margin, in order to attain a high-resolution velocity model of continental hyperextension. We have used several quality assurance procedures to assess the velocity model, including comparison of the observed and modeled waveforms, checkerboard tests, testing of parameter and inversion strategy and comparison with the migrated reflection image. Our final model exhibits an increase in the resolution of subsurface velocities, with particular improvement observed in the westernmost continental fault blocks, with a clear rotation of the velocity field to match steeply dipping reflectors. Across the S-reflector, there is a sharpening in the velocity contrast, with lower velocities beneath S indicative of preferential mantle serpentinization. This study supports the hypothesis that normal faulting acts to hydrate the upper-mantle peridotite, observed as a systematic decrease in seismic velocities, consistent with increased serpentinization. Our results confirm the feasibility of applying the FWI method to sparse, deep-water crustal data sets.