Water flow to the mantle transition zone inferred from a receiver function image of the Pacific slab
Water flow to the mantle transition zone inferred from a receiver function image of the Pacific slab
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DOI：
10.1016/j.epsl.2008.07.046
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发表时间：
2008-10
影响因子：
5.3
通讯作者：
T. Tonegawa;K. Hirahara;T. Shibutani;H. Iwamori;H. Kanamori;K. Shiomi
中科院分区：
文献类型：
--
作者：
T. Tonegawa;K. Hirahara;T. Shibutani;H. Iwamori;H. Kanamori;K. Shiomi
俯冲板片附近地震速度的变化对俯冲带的热结构和含水矿物及水的分布提供了制约。我们使用径向和横向接收函数（RF）研究了日本上地幔的地震学结构。径向RF可以成像速度对比的水平层，而横向RF可以成像倾斜层。这种组合使我们能够同时对水平和倾斜速度不连续性进行成像。我们调查了在678个Hi-net台站用倾斜仪观测到的45个地震事件的记录。我们使用的频带是从0.02到0.16 Hz。由此产生的RF图像显示了一个升高的410公里的不连续性，更重要的是，太平洋板块的顶面下降到低于410公里的不连续性。通过正演模拟，我们确定在深度超过200公里处，地幔楔的剪切波速度比俯冲板片慢约8%。地震速度的差异可能是由地幔楔底部的一系列含水矿物引起的，这些矿物接收了洋壳脱水反应释放的水。我们采用数值模拟，以确定水的分布和周围的俯冲板。结果表明，俯冲板片上方的含水矿物在相对较冷的条件下是持续稳定的，并将水携带到地幔过渡带。
Variations in seismic velocity near the subducting slab provide constraints on the thermal structure and the distribution of hydrous minerals and water in a subduction zone. We investigated the seismological structure in the upper mantle beneath Japan using both radial and transverse receiver functions (RFs). Radial RF can image horizontal layers of velocity contrast while transverse RF can image dipping layers. The combination allows us to simultaneously image both horizontal and dipping velocity discontinuities. We investigated the records of 45 teleseismic events observed with tiltmeters at 678 Hi-net stations. The frequency band we used is from 0.02 to 0.16 Hz. The resultant RF image shows an elevated 410 km discontinuity and, more importantly, the top surface of the Pacific slab down to below the 410 km discontinuity. With forward modeling, we determined that the mantle wedge is about 8% slower in shear-wave speed than the subducting slab at depths deeper than 200 km. The seismic velocity contrast is presumably caused by a sequence of hydrous minerals at the base of the mantle wedge which receives water released by dehydration reactions in the oceanic crust. We employed numerical simulations to determine the distribution of water in and around the subducting slab. The result suggests that hydrous minerals are continuously stable above the subducting slab in relatively cool conditions, and carry water to the mantle transition zone.