Dynamical links between small- and large-scale mantle heterogeneity: Seismological evidence
Dynamical links between small- and large-scale mantle heterogeneity: Seismological evidence
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DOI：
10.1016/j.epsl.2017.10.058
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发表时间：
2018-01
影响因子：
5.3
通讯作者：
D. Frost;E. Garnero;S. Rost
中科院分区：
文献类型：
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作者：
D. Frost;E. Garnero;S. Rost
摘要 我们从距离小于65°的小孔径地震台阵记录的地震中识别出PKP• PKP散射波（也称为P′• P'）。 P′• P′能量以PKP波的形式穿过核心，向上进入地幔，然后作为第二个PKP向下散射回接收器。 P′·P′波的独特之处在于它们可以对整个地幔的散射异质性进行成像。我们使用阵列处理方法来放大低振幅、相干散射能量信号并解析它们的传入方向。我们确定性地绘制从核幔边界到表面的散射异质性位置。我们使用对大量地幔敏感的广泛数据集和定位方法，使我们能够解析和绘制比以前更多的异质性，这代表我们对地幔内小尺度结构的理解显着增加。我们的结果表明，散射异质性的分布在径向和横向上都有变化。散射在最上层和最下层地幔中最丰富，在中地幔中最少，类似于断层扫描得出的全地幔速度不均匀性的径向分布。我们研究了散射异质性与大尺度层析速度、横向速度梯度、深部热点和俯冲板片位置的空间相关性。在地幔最下部 1500 公里处，小尺度的异质性与低地震速度、高横向地震梯度和接近热点的区域相关。在地幔上部 1000 km 范围内，散射异质性位置与俯冲板片之间不存在显着相关性。在 600 至 900 公里深度之间，散射异质性在距离板块最远且靠近热点的区域更为常见。散射异质性显示出对地幔上部 200 公里内接近板片的区域的亲和力。大尺度和小尺度地幔结构分布之间的相似性表明跨尺度的动态联系，由此各种尺寸的地幔异质性可能以类似的方式受到大尺度对流的引导。
Abstract We identify PKP• PKP scattered waves (also known as P′• P′) from earthquakes recorded at small-aperture seismic arrays at distances less than 65°. P′• P′ energy travels as a PKP wave through the core, up into the mantle, then scatters back down through the core to the receiver as a second PKP. P′• P′ waves are unique in that they allow scattering heterogeneities throughout the mantle to be imaged. We use array-processing methods to amplify low amplitude, coherent scattered energy signals and resolve their incoming direction. We deterministically map scattering heterogeneity locations from the core–mantle boundary to the surface. We use an extensive dataset with sensitivity to a large volume of the mantle and a location method allowing us to resolve and map more heterogeneities than have previously been possible, representing a significant increase in our understanding of small-scale structure within the mantle. Our results demonstrate that the distribution of scattering heterogeneities varies both radially and laterally. Scattering is most abundant in the uppermost and lowermost mantle, and a minimum in the mid-mantle, resembling the radial distribution of tomographically derived whole-mantle velocity heterogeneity. We investigate the spatial correlation of scattering heterogeneities with large-scale tomographic velocities, lateral velocity gradients, the locations of deep-seated hotspots and subducted slabs. In the lowermost 1500 km of the mantle, small-scale heterogeneities correlate with regions of low seismic velocity, high lateral seismic gradient, and proximity to hotspots. In the upper 1000 km of the mantle there is no significant correlation between scattering heterogeneity location and subducted slabs. Between 600 and 900 km depth, scattering heterogeneities are more common in the regions most remote from slabs, and close to hotspots. Scattering heterogeneities show an affinity for regions close to slabs within the upper 200 km of the mantle. The similarity between the distribution of large-scale and small-scale mantle structures suggests a dynamic connection across scales, whereby mantle heterogeneities of all sizes may be directed in similar ways by large-scale convective currents.