Localized ultra-low velocity zones at the eastern boundary of Pacific LLSVP
Localized ultra-low velocity zones at the eastern boundary of Pacific LLSVP
复制标题
太平洋LLSVP东边界局部超低速区
DOI：
10.1016/j.epsl.2018.11.037
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发表时间：
2019-02
期刊：
影响因子：
--
通讯作者：
Christine Thomas
中科院分区：
文献类型：
--
作者：
Xiaolong Ma;Xinlei Sun;Christine Thomas
研究表明，超低速带（ULVZ）往往位于大的低剪切速度带（LLSVP）的边界附近。以前的研究提供了证据，表明超低容量区存在于太平洋LLSVP的西部和北方边界的沿着。然而，到目前为止，还没有关于沿太平洋LLSVP东部边界沿着的超低容量区的详细报告。在这项研究中，我们收集了PKP前兆波形记录在南美洲的地震在澳大利亚的地震台阵。这些前体显示出清晰和连贯的相位。这些前兆的慢化和迁移分析表明，它们来自太平洋LLSVP以东地幔最下部的散射体。波形模拟表明，这些地震散射体是局部化的ULVZ，P波速度降低10.3 -10%，厚度为几十公里。ULVZs的尺寸和地质相关性的ULVZs与加拉帕戈斯热点，表明这些ULVZs主要是由于成分不同的异质性，虽然部分熔融不能完全排除。相干和非相干PKP前体的分布也表明了LLSVP边缘附近的小尺度地幔对流。
It is suggested that ultra-low velocity zones (ULVZs) are often located near the boundary of large low shear velocity zones (LLSVPs). Previous studies have provided evidence of ULVZs residing along the western and northern boundary of the Pacific LLSVP. However, so far there is no detailed report on ULVZs along the eastern boundary of the Pacific LLSVP. In this study, we collected PKP precursor waveforms from earthquakes in South America that are recorded by seismic arrays in Australia. These precursors show clear and coherent phases. Slowness and migration analysis of these precursors indicate that they originate from scatterers in the lowermost mantle east of the Pacific LLSVP. Waveform modeling suggests that these seismic scatterers are localized ULVZs, with P-wave velocity reductions of ∼3–10% and thickness of several tens of kilometers. The dimension of the ULVZs and the geological correlation of the ULVZs with the Galapagos hotspot, suggest that these ULVZs are mainly due to compositionally distinct heterogeneities, although partial melting cannot be completely ruled out. The distribution of both coherent and incoherent PKP precursors also suggests vigorous small-scale mantle convections near the edges of the LLSVP.
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