Constraining the 410-km discontinuity and slab structure in the Kuril subduction zone with triplication waveforms
Constraining the 410-km discontinuity and slab structure in the Kuril subduction zone with triplication waveforms
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DOI：
10.1093/gji/ggab361
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发表时间：
2021
影响因子：
2.8
通讯作者：
Jiaqi Li;Min Chen;J. Ning;Tiezhao Bao;R. Maguire;M. Flanagan;T. Zhou
中科院分区：
文献类型：
--
作者：
Jiaqi Li;Min Chen;J. Ning;Tiezhao Bao;R. Maguire;M. Flanagan;T. Zhou
410 km不连续面附近的详细结构提供了上地幔和下地幔通过地幔过渡带（MTZ）通过质量和热量交换的动力学相互作用的关键约束。同时，俯冲板片的温度，这可以从它的快波速度扰动，是了解俯冲带的地幔动力学的板片进入MTZ的关键。MTZ附近海底的多路径（即三重）体波携带着410 km不连续结构的丰富信息，可以用来约束不连续深度和波速的径向变化。具体地，我们说明了使用阵列归一化幅度的必要性。在千岛俯冲带的俄罗斯鞑靼海峡下面的两个一维深度剖面的波速获得。我们已经观察到由于410公里的不连续性和板片上表面的三倍。同时反演了这两个界面的地震构造。我们推导出的北方和南方地区410公里的不连续深度分别为420公里/分15公里和425公里/分15公里，没有可观察到的隆起。板片上表面被反演为位于410 km不连续面下方约50-70 km处。这个位置之间的深度的1%和2%的P波速度扰动轮廓的区域三维全波形反演（FWI）模型，但我们发现两倍的波速扰动幅度。与3-D FWI模型的2.0- 2.4%相比，板内的波速增加3.9- 4.6%，对于拟合具有最短2 s周期的波形是必要的，这表明需要高频波来准确地解析MTZ附近的详细结构。
The detailed structure near the 410-km discontinuity provides key constraints of the dynamic interactions between the upper mantle and the lower mantle through the mantle transition zone (MTZ) via mass and heat exchange. Meanwhile, the temperature of the subducting slab, which can be derived from its fast wave speed perturbation, is critical for understanding the mantle dynamics in subduction zones where the slab enters the MTZ. Multipathing, i.e. triplicated, body waves that bottom near the MTZ carry rich information of the 410-km discontinuity structure and can be used to constrain the discontinuity depth and radial variations of wave speeds across it. In this study, we systematically analysed the trade-off between model parameters in triplication studies using synthetic examples. Specifically, we illustrated the necessity of using array-normalized amplitude. Two 1-D depth profiles of the wave speed below the Tatar Strait of Russia in the Kuril subduction zone are obtained. We have observed triplications due to both the 410-km discontinuity and the slab upper surface. And, seismic structures for these two interfaces are simultaneously inverted. Our derived 410-km discontinuity depths for the northern and southern regions are at 420$\pm $15 and 425$\pm $15 km, respectively, with no observable uplift. The slab upper surface is inverted to be located about 50–70 km below the 410-km discontinuity. This location is between the depths of the 1 and 2 per cent P-wave speed perturbation contours of a regional 3-D full-waveform inversion (FWI) model, but we found twice the wave speed perturbation amplitude. A wave speed increase of 3.9–4.6 per cent within the slab, compared to 2.0–2.4 per cent from the 3-D FWI model, is necessary to fit the waveforms with the shortest period of 2 s, indicating that high-frequency waves are required to accurately resolve the detailed structures near the MTZ.