Crustal structure beneath China from receiver function analysis
Crustal structure beneath China from receiver function analysis
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DOI：
10.1029/2009jb006386
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发表时间：
2010-03
影响因子：
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通讯作者：
Youlin Chen;F. Niu;Rui-feng Liu;Zhi-bin Huang;H. Tkalčić;Li Sun;W. Chan
中科院分区：
文献类型：
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作者：
Youlin Chen;F. Niu;Rui-feng Liu;Zhi-bin Huang;H. Tkalčić;Li Sun;W. Chan
[1]我们收集和处理了中国国家数字地震台网48个台站的高质量宽频带地震波形数据，以估计中国大陆地壳厚度和Vp/Vs比（泊松比）的大尺度横向变化。使用统计方法在每个台站选择相互相干的接收机功能，为大多数台站提供了200多条记录道。在传统的H−κ（地壳厚度和Vp/Vs比值）方法中，H和κ之间存在很大的权衡。因此，在H−κ结构域中经常观察到多个极大值。我们引入了一个权重函数，用于测量每个H−κ网格处P-to-S转换和混响相位之间的相干性，以减少权衡。进一步应用4次根叠加方法来减少相对于线性叠加的不相关噪声。这些修正被证明在减少H−κ权衡方面非常有效，并产生了可靠的地壳厚度和Vp/Vs比的估计。中国东部地壳厚度为31-33 km，莫霍面相对平坦而尖锐。中国西部地壳厚度大，变化大。沿天山褶皱系沿着51 km深度处和青藏高原中部84 km深度处观测到莫霍面。这种转换发生在东经100° ~ 110°之间的所谓南北带，其特点是异常高的地震活动和大的重力异常。中国大陆地壳的平均Vp/Vs值约为1.730（σ = 0.249），明显低于全球大陆地壳的平均值1.78（σ = 0.27）。这种较低的Vp/Vs比值可能表明中国大陆地壳最低层普遍缺乏镁铁质。
[1] We collected and processed a large amount of high-quality broadband teleseismic waveform data recorded by the 48 Chinese National Digital Seismic Network stations to estimate large-scale lateral variations of crustal thickness and Vp/Vs ratio (hence Poisson's ratio) beneath China. A statistical method was used to select mutually coherent receiver functions at each station, which yielded over 200 traces for most of the stations. With the conventional H−κ (the crustal thickness and Vp/Vs ratio) approach, there is a large trade-off between H and κ. Consequently, multiple maxima are frequently observed in the H−κ domain. We introduced a weight function that measures the coherence between the P-to-S conversion and the reverberation phases at each H−κ grid to reduce the trade-off. A 4th-root stacking method was further applied to reduce uncorrelated noise relative to the linear stack. These modifications turned out to be very effective in reducing the H−κ trade-off and yielded reliable estimates of crustal thickness and Vp/Vs ratio. The crust beneath eastern China is as thin as 31–33 km and the underlying Moho is relatively flat and sharp. In the western part of China, the crust is considerably thicker and shows large variations. The Moho is observed at about 51 km depth along the Tian Shan fold system and about 84 km deep beneath the central part of the Tibetan Plateau. The transition occurs at the so-called N-S belt between about 100° and 110°E, which is featured by unusually high seismicity and large gravity anomalies. The average Vp/Vs ratio over the mainland China crust is about 1.730 (σ = 0.249), significantly lower than the global average 1.78 (σ = 0.27) of the continental crust. This lower Vp/Vs ratio may suggest a general absence of mafic lowermost crustal layer beneath China.