北京地区地壳精细结构的深地震反射剖面探测研究

长度100 km、NW向穿过三河—平谷8.0级地震区和北京地区主要断裂构造的深地震反射剖面，揭示了该区地壳精细结构图像和断裂的深浅构造特征.结果表明，该区地壳以TWT6～7 s左右的强反射带为界分为上地壳和下地壳，上地壳厚约18～21 km，下地壳厚约13～15 km.剖面TWT3～4 s以上，反射层位丰富，构造形态清晰，且在剖面上具有明显不同的构造特征；在三河—平谷地震区以西，剖面揭示了2～3组反射能量较强的反射震相和一系列错断基底面的断裂，在三河—平谷地震区以东，为一套自东向西倾伏的密集强反射层，这套反射具有典型的沉积盆地特征，盆地最深处约为8～9 km.剖面揭示的地壳深断裂倾角陡直，该断裂切割、扰动了下地壳物质和壳幔过渡带，向上延伸至上地壳，将地壳深部构造与浅部断裂联系在一起，构成了该区最主要的深浅构造特征.

Research on fine crustal structure using deep seismic reflection profile in Beijing region

The fine crustal structure and deep-shallow tectonic features of Beijing region are explored by using a 100 km long，NW-trending deep seismic reflection profile. This profile passed through the Sanhe-Pinggu earthquake (M8.0) area and main faults in Beijing region. The results show that the crust beneath the investigated area is divided into upper and lower crust by a strong reflective zone at about 6～7 s TWT. The thickness of the upper and lower crust is about 18～21 km and 13～15 km, respectively. There are rich reflective layers and clear structural patterns above 3～4 s TWT as well as obviously different structural features along the profile. In the western region of Sanhe-Pinggu earthquake area, the stacked deep seismic reflection section shows 2～3 groups of strong reflective layers and a series of basement faults. In the eastern region of Sanhe-Pinggu earthquake area, there is a set of dense, westward-dipping, reflective strata with relatively strong energy, which have the typical characteristics of sedimentary basin. The largest depth of the sedimentary basin is about 8～9 km. The crustal deep fault revealed by deep seismic reflection profile has a steep fault plane, and it cuts and disturbs the lower crust and crust-mantle transitional zone. This deep fault extends upwards into the upper crust, and joins the crustal deep structure to the shallow fault. The profile reveals that the deep-shallow fault system represents the major deep-shallow tectonic feature in the study region.