Sedimentary Structure Derived From Multi‐Mode Ambient Noise Tomography With Dense OBS Network at the Japan Trench
Sedimentary Structure Derived From Multi‐Mode Ambient Noise Tomography With Dense OBS Network at the Japan Trench
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DOI：
10.1029/2021jb021789
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发表时间：
2021-04
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影响因子：
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通讯作者：
Lina Yamaya;K. Mochizuki;T. Akuhara;K. Nishida
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作者：
Lina Yamaya;K. Mochizuki;T. Akuhara;K. Nishida
通过对密集的短周期海底地震仪(OBS)进行环境噪声层析成像，得到了日本海沟俯冲带茨城附近地区沉积物和上地壳的三维S波速度结构。利用27天和142天的连续地震资料计算了交叉谱，得到了0.1-0.25 Hz和0.17-0.3 Hz频率范围内基模和一阶高阶瑞利波的相速度。基于跨维马尔可夫链蒙特卡罗方法的一维S波速反演揭示了声学基底上方的多个沉积层和上地壳结构。然后以一维结构为参考模型，通过采集当地一维S波速度结构数据，进行了环境噪声层析成像和三维S波速度结构的非线性反演。我们的三维S波速度结构揭示了三个要点：(A)声波基底位于∼4公里深；(B)地壳结构比沉积层更复杂；(C)南部地区具有复杂的地壳结构，以前的P波速度层析成像识别了俯冲海山。
We derive the 3‐D S‐wave velocity structures of sediments and upper crust in the region off Ibaraki at Japan Trench subduction zone by applying ambient noise tomography to a dense array of short‐period ocean bottom seismometers (OBSs). The cross‐spectra were calculated using 27 or 142‐day continuous seismic data, and the phase velocities of the fundamental and the first‐higher Rayleigh wave modes are obtained in the frequency ranges of 0.1–0.25 Hz and 0.17–0.3 Hz, respectively. Our 1‐D S‐wave velocity inversion based on the trans‐dimensional Markov chain Monte Carlo method revealed multiple sedimentary layers above the acoustic basement and the upper crustal structure. The 1‐D structure was then used as a reference model to conduct ambient noise tomography and non‐linear inversion of the 3‐D S‐wave velocity structure by collecting data of the local 1‐D S‐wave velocity structure. Our 3‐D S‐wave velocity structure revealed three main points: (a) The acoustic basement is situated at a depth of ∼4 km depth; (b) the crustal structure is more complex than that of the sedimentary layers; and (c) the southern region has a complex crustal structure in which subducting seamounts were identified by previous P‐wave velocity tomographies.