Mantle earthquakes in the Himalayan collision zone
Mantle earthquakes in the Himalayan collision zone
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DOI：
10.1130/g46378.1
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发表时间：
2019-09
期刊：
影响因子：
5.8
通讯作者：
V. Schulte‐Pelkum;G. Monsalve;A. Sheehan;P. Shearer;Francis T. Wu;S. Rajaure
中科院分区：
文献类型：
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作者：
V. Schulte‐Pelkum;G. Monsalve;A. Sheehan;P. Shearer;Francis T. Wu;S. Rajaure
据了解，地震发生在西藏南部地下，深度可达 95 公里。这些地震是发生在喜马拉雅碰撞增厚的下地壳内，还是发生在地幔内，目前仍存在争议。在这里，我们将表示为本地事件的 S 和 P 到达之间的延迟时间的垂直行进路径与接收器函数中莫霍面的 P 到 S 转换的延迟时间进行比较。该方法消除了使用速度模型进行深度定位和偏移的标准分析中引入的大部分不确定性。我们表明，西藏南部的深层地震活动明确位于地幔莫霍面下方。大陆岩石圈的深层地震活动发生在通常的延性条件下，因此引起了人们的兴趣，即其发生是由于特别寒冷的温度还是其他因素导致延性材料的脆化。俯冲印度地壳中的榴辉岩作用被认为是该地区深部地震活动的原因。我们对地幔中地震活动的观察，在提出的榴辉岩化作用下落在地壳层之下而不是在地壳层内，需要重新审视这个概念，并支持在地幔物质内运作的其他脆化机制。
Earthquakes are known to occur beneath southern Tibet at depths up to ∼95 km. Whether these earthquakes occur within the lower crust thickened in the Himalayan collision or in the mantle is a matter of current debate. Here we compare vertical travel paths expressed as delay times between S and P arrivals for local events to delay times of P-to-S conversions from the Moho in receiver functions. The method removes most of the uncertainty introduced in standard analysis from using velocity models for depth location and migration. We show that deep seismicity in southern Tibet is unequivocally located beneath the Moho in the mantle. Deep seismicity in continental lithosphere occurs under normally ductile conditions and has therefore garnered interest in whether its occurrence is due to particularly cold temperatures or whether other factors are causing embrittlement of ductile material. Eclogitization in the subducting Indian crust has been proposed as a cause for the deep seismicity in this area. Our observation of seismicity in the mantle, falling below rather than within the crustal layer with proposed eclogitization, requires revisiting this concept and favors other embrittlement mechanisms that operate within mantle material.