Lateral Variations of Shear‐Wave Velocity in the D″ Layer Beneath the Indian‐Eurasian Plate Collision Zone
Lateral Variations of Shear‐Wave Velocity in the D″ Layer Beneath the Indian‐Eurasian Plate Collision Zone
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DOI：
10.1029/2019gl086856
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发表时间：
2020-03
影响因子：
5.2
通讯作者：
Guohui Li;L. Bai;J. Ritsema
中科院分区：
文献类型：
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作者：
Guohui Li;L. Bai;J. Ritsema
地震层析成像表明，在南亚和东亚最低地幔3000公里宽的区域内，横波速度相对较高。这一地震异常标明了白垩纪可能已经俯冲的板岩残留物的当前位置。为了进一步刻画小尺度上的地震结构，我们利用中国数字地震台网的印度洋下8次地震的记录，测量了SCS和S震相之间的929个剩余走时差(δt)。我们将高达10 S的δt的变化解释为印度北部、尼泊尔和中国西南部D“的水平剪切速度变化所致。在短于300公里的距离上，剪切速度的变化可能高达7%。我们的观察提供了更多的观测证据，表明成分的不均一性和可能的熔融有助于以长期俯冲和地幔下涌为特征的下地幔的地震结构。
Seismic tomography has demonstrated that the shear‐wave velocity is relatively high over a 3,000‐km wide region in the lowermost mantle beneath southern and eastern Asia. This seismic anomaly demarcates the current position of slab remnants that may have subducted in the Cretaceous. To further characterize the seismic structure at smaller scales, we measure 929 residual travel time differences (δt) between the phases ScS and S using recordings of eight earthquakes beneath the Indian Ocean at stations from the Chinese Digital Seismic Network. We interpret variations of δt up to 10 s as due to horizontal shear‐velocity variations in D″ beneath northern India, Nepal, and southwestern China. The shear velocity can vary by as much as 7% over distances shorter than 300 km. Our observations provide additional observational evidence that compositional heterogeneity and possibly melt contribute to the seismic structure of the lower mantle characterized by long‐term subduction and mantle downwelling.