IMAGE THE ZHEFANG-BINCHUAN AND MONGLIAN-MALONG WIDE-ANGLE SEISMIC PROFILES IN YUNNAN PROVINCE
IMAGE THE ZHEFANG-BINCHUAN AND MONGLIAN-MALONG WIDE-ANGLE SEISMIC PROFILES IN YUNNAN PROVINCE
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DOI：
10.1002/cjg2.484
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发表时间：
2004-03
期刊：
影响因子：
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通讯作者：
Z. Bai;Chun-yong Wang
中科院分区：
文献类型：
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作者：
Z. Bai;Chun-yong Wang
利用地球物理走时、振幅比和布格重力异常资料，采用有限差分反演和射线反演方法，对云南遮放-宾川和孟连-M沿着宽角地震剖面的地壳上地幔结构进行了沿着反演。从而对地球动力学和地震构造环境提出了新的认识。遮放-宾川剖面地壳厚度沿着为35~ 46 km，孟连-M沿着为33~44.5km。莫霍界面的几何形状与胡宏新等给出的相似，部分地区下地幔顶部的P波速度较低，且速度变化幅度较大，这可能表明云南地区是一个典型的活动构造区。而且，浅部和深部结构具有显著的一致性，这意味着浅部物质的活动总是有深部背景的。遮放-宾川剖面的速度结构表明，出露在地表的怒江断裂以东存在一个贯穿整个地壳的大的低速异常，这可能与深部物质的上涌有关。从这两条速度结构剖面上还可以推断出作为一级构造单元边界的大断层的特征：红河断裂是一条切割岩石圈的超断层，怒江断裂在地壳中切割较深，甚至向下延伸到上地幔顶部，而昌宁-双江断裂则呈铲状，倾角较小，这可能表明其切口深度不是很深。云南地区的大地震往往与上地幔深大断裂有关。一些震源深度较浅的地震，一般位于中上地壳内不同断裂的交汇处或高、低速异常块体之间的带上速度等值线弯曲处。据估计，这些地点有利于能量和区域应力的积累。
Based on the finite difference inversion and ray inversion method, the crust and upper mantle structure along the Zhefang–Binchuan and Menglian–Malong wide–angle seismic profiles, both of which are located in Yunnan province, are imaged using the geophysical data of travel-time, amplitude ratio and Bouguer gravity anomalies. Thus some new recognitions about the geodynamics and the seismotectonic environment are derived. The crust thickness along the Zhefang–Binchuan profile is 35~46km, and that of the Menglian–Malong profile is 33~44.5km. The geometry of the Moho interface looks like that given by Hu H X et al. The P wave velocity on the top of the mantle beneath some places is relatively low and the variation range of the velocity is very large, which may indicates that the Yunnan region is a typical area of active tectonics. Moreover, there exits a prominent consistency between the shallow and deep structures, which implies that the activity of shallow material always has a deep background. The velocity structure of Zhefang–Binchuan profile indicates that there exists a large low velocity anomaly which penetrates the whole crust to the east of the Nujiang fault exposed on the ground, and this possibly associated with the upwelling of the deep material . The characteristic of the large faults which are the borders between some first order tectonic units can also be derived from the both velocity structure profiles: the Red River fault is a hyper-fault that cuts the lithosphere, the Nujiang fault cuts deeply in the crust and even stretches downward into the top of the upper mantle, yet the Changning–Shuangjiang fault has a listric shape with a small dip angle, which may suggest that its incision depth is not very deep. The large earthquakes took place in Yunnan province always have a relationship with the large and deep faults that stretches into the upper mantle. Some earthquakes with shallow focal depths are generally located at the converge positions of different faults within the upper-middle crust or the places where the velocity contours on the belt between the high and low velocity anomaly blocks are crooked. It is estimated that these locations are favorable to the accumulation of energy and regional stress.