Imaging the Shallow Subsurface Structure of the North Hikurangi Subduction Zone, New Zealand, Using 2-D Full-Waveform Inversion
Imaging the Shallow Subsurface Structure of the North Hikurangi Subduction Zone, New Zealand, Using 2-D Full-Waveform Inversion
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使用二维全波形反演对新西兰北 Hikurangi 俯冲带的浅层地下结构进行成像
DOI：
10.1029/2019jb017793
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发表时间：
2019
期刊：
影响因子：
3.4
通讯作者：
Gray M
中科院分区：
文献类型：
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作者：
Gray M
北Hikurangi板块边界断层具有一系列地震行为，其中控制地震活动性的物理机制尚不清楚，但通常与高孔隙流体压力和条件稳定的摩擦条件有关。利用2维海洋地震流数据，我们采用全波形反演（FWI）获得了Hikurangi边缘深度约2公里的高分辨率2 - DPwave速度模型。通过与叠前深度偏移地震反射图像、声波井数据以及观测波形和合成波形的匹配，研究了FWI速度模型的有效性。我们的模型揭示了覆盖板块的浅层结构，包括慢滑事件带上方的断层管道系统，其理论分辨率为半地震波长。研究发现，逆冲断层上盘的速度往往明显高于下盘，与较高的压实作用相一致。在某些情况下，从反射数据中识别出的楔内断层与低速异常有关，这可能表明它们是作为流体流动管道的高孔隙度带。远离国际海洋发现计划钻探地点U1520的速度结构的连续性表明，在该地点观察到的进入沉积地层的岩性变化持续到变形前沿，可能对控制地震行为很重要。这项研究提供了对俯冲带浅层部分的高分辨率洞察，这表明了利用最近获得的长偏移地震数据集将建模扩展到三维的希望。
The northern Hikurangi plate boundary fault hosts a range of seismic behaviors, of which the physical mechanisms controlling seismicity are poorly understood, but often related to high pore fluid pressures and conditionally stable frictional conditions. Using 2‐D marine seismic streamer data, we employ full‐waveform inversion (FWI) to obtain a high‐resolution 2‐DPwave velocity model across the Hikurangi margin down to depths of ~2 km. The validity of the FWI velocity model is investigated through comparison with the prestack depth‐migrated seismic reflection image, sonic well data, and the match between observed and synthetic waveforms. Our model reveals the shallow structure of the overriding plate, including the fault plumbing system above the zone of slow‐slip events to theoretical resolution of a half seismic wavelength. We find that the hanging walls of thrust faults often have substantially higher velocities than footwalls, consistent with higher compaction. In some cases, intrawedge faults identified from reflection data are associated with low‐velocity anomalies, which may suggest that they are high‐porosity zones acting as conduits for fluid flow. The continuity of velocity structure away from International Ocean Discovery Program drill site U1520 suggests that lithological variations in the incoming sedimentary stratigraphy observed at this site continue to the deformation front and are likely important in controlling seismic behavior. This investigation provides a high‐resolution insight into the shallow parts of subduction zones, which shows promise for the extension of modeling to 3‐D using a recently acquired, longer‐offset, seismic data set.