Seismic Tomographic Imaging of the Crust and Upper Mantle Beneath the Northeastern Edge of the Qinghai‐Xizang Plateau and the Ordos Area
Seismic Tomographic Imaging of the Crust and Upper Mantle Beneath the Northeastern Edge of the Qinghai‐Xizang Plateau and the Ordos Area
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DOI：
10.1002/cjg2.566
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发表时间：
2004-09
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影响因子：
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通讯作者：
B. Guo;Qi-yuan Liu;Jiuhui Chen;Dapeng Zhao;Shun-cheng Li;Yuan‐Gen Lai
中科院分区：
文献类型：
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作者：
B. Guo;Qi-yuan Liu;Jiuhui Chen;Dapeng Zhao;Shun-cheng Li;Yuan‐Gen Lai
利用地震层析成像技术，研究了鄂尔多斯地区和青藏高原东北部400公里深处地壳和上地幔的P波速度结构。所使用的数据分别取自区域网络的记录和整个调查区域的被动地震观测剖面。结果表明，地壳上地幔速度结构沿剖面沿着有明显的横向变化，这种变化不仅存在于不同块体之间，而且存在于块体内部。青藏高原东北缘地壳和上地幔的平均P波速度较低，鄂尔多斯块体的平均P波速度高于全球模型。我们的观测结果与这两个地块的构造活动相吻合。青藏块体东北部与鄂尔多斯块体之间存在一条宽约200km的过渡带，该过渡带在地表上相当于兰州与海原之间的地区。上地幔的过渡带呈向东倾斜约45 °的条纹状。它的主要特征表现为高速和低速介质的混合。该条带在上地幔中的走向似乎受鄂尔多斯地块下的高速体控制。这表明稳定的鄂尔多斯地块对青藏高原的东移具有一定的抵抗作用。青藏高原柴达木盆地上地幔速度结构为低平均速度结构，祁连地块上地幔速度结构为高平均速度结构。两者之间的差距达到8%左右。在泽库、兰州和海原地区的上地幔中也分别发现了低速侵入体。南北地震带的高地震活动性与介质的非均匀性和特殊的深部动力学环境密切相关。
We investigate the P-wave velocity structure of the crust and upper mantle down to depth 400km beneath the Ordos region and northeastern Qinghai-Xizang plateau using the seismic tomographic technique. The data used are taken from the record by the regional network and a passive seismic observation profile across the investigated area, respectively. Our results show clear lateral variations of the crust and upper mantle velocity structure along the profile, which exist not only between different blocks, but also inside blocks. The average P-wave velocity of the crust and upper mantle beneath the northeastern margin of the Qinghai-Xizang plateau is lower, and that beneath the Ordos block is higher than the global model. Our observations are coincident with the tectonic activities of these two blocks. Between the northeastern Qinghai-Xizang and Ordos block exists a transition zone about 200km wide, which on the surface corresponds to the region between Lanzhou and Haiyuan. This transition zone in the upper mantle appears as a stripe with a slope of about 45- tilting eastward. Its main feature appears as a mixture of high- and low-velocity media. The strike of this stripe in the upper mantle seems to be controlled by the high-velocity body beneath the Ordos block. This implies that the stable Ordos block plays a role in resisting the eastward movement of the Qinghai-Xizang plateau. The upper mantle velocity structure beneath the Qaidam basin in the Qinghai-Xizang plateau has a low average velocity and that beneath the Qilian block has a high average velocity. The difference between both reaches about 8%. We also find the intrusive low-velocity bodies in uppermost mantle beneath Zekog, Lanzhou and Haiyuan areas, respectively. The high seismicity in the north-south seismic zone should be related closely to the medium heterogeneity and very special deep dynamic environment.