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位于南北地震带南段的滇西南地区是中国地质构造运动和地震活动较为强烈的地区之一.该区的地质构造背景和深部物理场特征研究是重要的基础科学问题.2013年,在滇西南地区完成了一条长600 km的勐海-耿马-泸水深地震宽角反射/折射和高分辨地震折射联合探测剖面,利用获得11次爆破地震记录截面上6组清楚的壳内P波震相,采用有限差分反演和射线走时正演拟合技术构建了该区的基底速度结构和地壳二维P波速度结构模型.结果显示:沿剖面地壳厚度由南向北逐渐加厚,基底形态呈现出明显的横向起伏变化,在南汀河断裂带附近,基底结构呈现出凹、隆相间的变化形态,基底埋深最浅处约为1.0 km,在腾冲与澜沧附近,基底埋深约为5.0 km.该区中、下地壳速度总体呈现出随深度的增加而增大的变化特征,在块体边界和断裂构造带的下方,速度等值线出现明显紊乱和P波速度的突变.本区莫霍面深度由南向北逐渐加深,且横向起伏变化较大,莫霍面最浅处位于勐海附近,其深度约为32.0 km,最深处位于腾冲附近,深约40.5 km.在耿马与永德之间,莫霍面出现快速上隆和下凹的明显变化,其变化幅度约为4.0 km.在南汀河断裂带、龙陵-瑞丽断裂、大盈江断裂和腾冲火山区的下方,基底速度结构、地壳二维P速度结构、剖面平均速度分布和壳内界面展布还出现从基底至莫霍面顶部的明显变化,显示出断裂构造带下方的地壳速度和介质物性与其两侧的地壳物质具有明显的差异,暗示这些断裂不但具有一定的规模,而且可能延伸至下地壳或上地幔顶部.该区地震主要发生在10~20 km的深度范围内,且地震活动呈现出与壳内介质速度差异、断裂带分布的相关性.研究结果可为分析研究滇西南地区地震活动的深部构造背景、地震精确定位、构建发震构造模型等提供重要的壳幔结构数据,为评价该区的地震危险性和防震减灾规划的制定提供重要参考.
The southwestern Yunnan region, located in the southern segment of the North-South Seismic Belt, is one of the regions where geologic tectonic movement and seismicity are relatively strong in China.The study on the geotectonic background and deep physical characteristics of the area is an important basic scientific issue.In 2013, A 600 km long Menghai-Gengma-Lushui deep seismic reflection / refraction and high-resolution seismic refraction joint detection profile was completed. Six clear sets of intra-shell P-wave seismic phases were obtained from eleven blasting seismic records , The basement velocity structure and two-dimensional P-wave velocity structure model of the crust were constructed by Finite-Difference Inversion and forward modeling with time-of-flight. The results show that the thickness of crust along the section increases gradually from south to north, In the vicinity of the Nantinghe fault zone, the basement structure showed a concave-long-surfaced alternation pattern. The shallowest depth of the basement was about 1.0 km. In the vicinity of Tengchong and Lancang, the basement depth was about 5.0 km. The middle and lower crustal velocities generally show the characteristics of the increase with depth increasing. Under the boundary of the block and below the fault zone, the velocity contour shows obvious disorder and P-wave velocity The depth of the Moho decreases gradually from south to north, and the horizontal fluctuation changes greatly. The shallowest Moho area is located near Menghai with a depth of about 32.0 km and the deepest is located near Tengchong at a depth of about 40.5 km . Between Gengma and Yongde, there was a clear change in the fast uplift and depression of the Moho with an amplitude of about 4.0 km. In the Nandinghe fault zone, Longling-Ruili fault, Dayingjiang fault and Below the Tengchong volcanic area, the velocity structure of the basement, the two-dimensional velocity structure of the crust, the average velocity profile in the crust, and the in-shell interface distribution also show significant changes from the base to the top of the Moho, indicating the crustal velocity beneath the fault zone and There is a significant difference between the physical properties of the medium and the crustal materials on both sides of the crust, suggesting that these fractures not only have a certain scale but may extend to the lower crust or the upper mantle, where the earthquakes occur mainly in the depth of 10 ~ 20 km and the earthquakes The activity shows the correlation with the difference of velocity and the distribution of fault zone in the crust.The results of this study can be used to analyze the deep tectonic setting of seismic activity in southwest Yunnan, to locate the earthquake accurately and to construct the seismogenic structure model Crust-mantle structure data to provide important reference for the evaluation of the development of seismic hazard and earthquake disaster mitigation planning of the area.