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Subcrustal Low Velocity Layers in Central India and their Implications

机译：印度中部的亚壳低速层及其意义

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摘要

A 2-D subcrustal velocity model for the central Indian continental lithosphere has been derived by travel time and relative amplitude modeling of a digitally normalized analog seismic record section of the Hirapur-Mandla DSS profile, using a ray-tracing technique. Some prominent wave groups with apparent velocities slightly higher than the Moho reflection phase (PMP) are identified on the normalized record sections assembled with a reduction velocity of 6 km s−1. We interpret these phases as the wide-angle reflections from subcrustal lithospheric boundaries. Comparison of synthetic seismograms with the observed record section shows that the observed phases cannot be explained either by multiples or by the P-to-S converted phase (PMS) from the Moho. Subcrustal velocity models either with a velocity increase or with a single low velocity layer (LVL) also do not provide a satisfactory fit. We infer that a subcrustal velocity model with two alternate LVLs (velocity 7.2 km s−1), separated by a 6-km thick high velocity layer (velocity 8.1 km s−1), can satisfy both the observed travel times and amplitudes. The prominent reflection phases are modeled at depths of 49, 51, 57 and 60 km. It is inferred that the subcrustal lithosphere in the central Indian region has a lamellar structure with varying structural and mechanical properties. The alternating LVLs, occurring at relatively shallow depths below Moho, may be associated with the zones of weakness and lower viscosity suggesting continued mobility, with a possible thermal source in the upper mantle. This explains the source of observed high heat flow values in the central Indian region.
机译：通过使用射线追踪技术，通过对Hirapur-Mandla DSS剖面的数字标准化模拟地震记录部分的传播时间和相对振幅模型，得出了印度中部大陆岩石圈的二维亚地壳速度模型。在归一化记录段上，以约6 km s-1 的减速速度识别出一些明显的波速明显高于莫霍反射相（PM P）的显着波群。我们将这些相解释为来自地壳下岩石圈边界的广角反射。合成地震图与观测记录段的比较表明，观测相不能用莫霍面的倍数或P-S转换相（PM S）来解释。具有速度增加或具有单个低速层（LVL）的亚地壳速度模型也不能提供令人满意的拟合。我们推断出一个具有两个交替LVL（速度7.2 km s-1 ），被6公里厚的高速层（速度8.1 km s-1 ）隔开的地壳下速度模型可以满足这两个条件观察到的传播时间和幅度。突出的反射相位在49、51、57和60 km的深度处建模。可以推断，印度中部地区的地壳下岩石圈具有层状结构，具有不同的结构和力学性质。发生在莫霍面以下相对较浅深度的交替LVL可能与薄弱和粘性较低的区域有关，表明持续的流动性，而上地幔中可能有热源。这解释了在印度中部地区观测到的高热流值的来源。

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