【摘要】 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13-1 5 km.剖面TWT3-4s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.更多还原

【Abstract】 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.更多还原