玉溪—临沧剖面宽角地震探测——红河断裂带及滇南地壳结构研究

Wide angle seismic exploration of Yuxi-Lincang profile——The research of crustal structure of the red river fault zone and southern Yunnan

云南位于南北地震带南段,地震活动具有频度高、强度大的特点,中小地震几乎遍及云南南部,是中国大陆内部地震活动最强的地区之一.滇南地区跨越多个重要的地质构造单元和多条地震带,其中红河断裂带是跨越该地区的一条大型的走滑断裂带,作为印支地块和华南地块两大地块的分界断裂,对人们认识板块相互运动及其深部动力学背景具有重要意义.中国地震局于2010年启动了"中国地震科学台阵探测——南北地震带南段"项目,在云南省中西部跨越红河断裂带布设一条近东西向的深地震宽角反射/折射探测剖面,本文利用该东西向深地震宽角反射/折射剖面来研究红河断裂带及滇南地区详细的地壳结构及其孕震背景.研究结果表明:沿测线地壳结构呈西薄东厚的特征,以红河断裂带为界,断裂带以西地壳较薄,约34km,以东地壳加厚至44km左右;红河断裂带两侧速度结构具有明显的差异,断裂带西侧速度较低,东侧速度明显偏高.由震相特征及获取的地壳结构可以看出,红河断裂带两侧由浅至深速度结构的异常特征说明该古缝合带两侧块体地壳结构岩性的巨大差异性.

Yunnan province is located in the southern section of North South seismic belt,the seismicity of this area has the features of high frequency,high strength,and small earthquakes are almost everywhere;it is one of the strongest earthquake regions in the China continental interior.Southern Yunnan crosses a number of important geological tectonic units and series of seismic belts.Among them,the red river fault zone is a large strike slip fault zone crossing Yunnan province,and as the boundary fault between Indochina block and South China block,ithas important significance for understanding the interaction of plates and geodynamic background.In2010,China Earthquake Administration launched the China seismological array exploration project——southern section of North South seismic belt.According to the research purpose and requirements of this project,a nearly EW-trending deep seismic wide-angle reflection/refraction profile was laid out across the Red River fault zone in central and western Yunnan.In this paper,the crustal structure and seismogenic background of the Red River fault zone and the southern Yunnan area is studied by using this sounding profile.The results show that：the crust along this profile thickens from west to east,which is probably bounded by red river fault zone,the west part is thinner,about 34 km,the east part is thicker,about 44 km.There is obvious difference in the velocity structure on the two sides of the red river fault zone,and the velocity is lower in west and significantly higher in east.From the seismic phase and the crustal structure we obtained,the two sides of the red river fault zone are characterized of different crustal structure from shallow to deep,which demonstrates great difference of lithology on the two sides of this paleo suture.