洱源-江川宽角地震剖面的地壳反射特征

Crustal reflectivity characters from the Eryuan-Jiangchuan wide-angle seismic profile

通过对洱源-江川宽角反射地震资料的叠前偏移处理成像,得到了一个类似于近垂直入射多道地震数据的记录剖面.反射剖面图像与地壳速度结构共同揭示出地壳厚度由剖面西北端(约45km)向东南端(约40km)减薄.在洱源-楚雄西北附近深度约10km处存在一组向东南倾斜的强反射震相,其东南约50km处存在向西北倾斜的强反射震相.易门断裂两侧地壳反射属性具有明显的差异,易门断裂之西北方向深度25～40km处,中下地壳内存在两组强振幅,向东南方向上倾的地震反射同相轴,并被楚雄-建水断裂后期所错断,易门断裂之东南方向上,地壳内反射较为均一,未见特别明显的强间断面反射信息,这个反射结构被解释为印度板块东向俯冲与藏东缘地壳物质东向逃逸综合作用导致下地壳增厚和厚地壳变形的结果.

By prestack migration processing to the wide angle reflection seismic data of the Eryuan-Jiangchuan profile in Yunnan Province,we obtain a crustal reflectivity section which is similar to nearly-vertical incidence seismic data. Both the reflectivity image and the crustal velocity structure jointly demonstrate that the crustal thickness thins from about 45 km on the northwestern end of the profile to about 40 km on the southeastern end. Near the northwest of Eryuan and Chuxiong, there are a series of southeast-dipping strong reflectors at depth 10 km and a series of northwest-dipping strong reflection 50 km to its southwest. Crustal reflection attributes obviously differ on the both sides of the Yimen fault. To the northwest of the Yimen fault, two sets of reflectors with strong amplitude dipping upwards lie in the middle-lower crust of depths 25 - 40 km, and are cut by the Chuxiong-Jianshui fault. To the southeast of Yimen fault, no obvious strong discontinuous reflection appears in the crust. This unique crustal velocity structure and reflectivity images are explained to be the results of thickening and deformation of crust under the joint action of Indian plate＇s eastward subduction and eastward escape of the crustal material at the eastern margin of Tibet.