【摘要】 在 1679年三河 -平谷 8 0级大震的震源区布置了两条总长 140km ,2 4次覆盖的近垂直深地震反射剖面 ,剖面穿过夏垫断裂及二十里长山断裂。结果表明 ,该区以双程走时 7 0s(2 1km)左右和 11 0～ 12 5s(33～ 37km)左右的两个强反射叠层把地壳分为上地壳、下地壳和壳幔过渡带 ;地壳结构在纵向上差异较大 ,浅部成层性较好 ,层组较多 ,结构复杂 ;上地壳总体呈反射“透明”性质 ,下部地壳表现为明显的反射性质 ;在横向上也具有明显的差异 ;深部断裂主要有夏垫断裂下方的地壳深断裂 ,断层面较陡 ,近于直立 ,该断裂可能为三河 -平谷 8 0级大地震的发震断裂 ;分别在两条剖面下地壳和上地壳下部存在局部强反射能量团 ,应为上地幔物质上涌冷却形成的岩墙或岩体 ;由于该处的岩浆活动造成了局部应力分布的差异 ,导致了地壳深断裂的形成 ,这可能是三河 8 0级大震的深部构造背景更多还原

【Abstract】 Two near vertical deep seismic reflection profiles (140km long, 24 fold) were completed in the 1679 Sanhe Pinggu earthquake ( M 8 0) region, running through the Xiadian fault and Ershilichangshan fault. The result shows that crust in the region is divided into the upper crust, the lower crust and the crust mantle transitional zone by two strong reflections (one at the depth of 21km with a two way traveltime of about 7 0s, the other at 33～37km with two way traveltime 11 0～12 5s). Crustal structure varies significantly in vertical direction: the shallow part is characterized by obvious stratification, multilayers and complicated structure; the upper crust features reflection “transparency" on the whole, while the lower crust features distinct reflectivity. Obvious differences are also seen in lateral direction. The main fracture in this region is the crustal fault under Xiadian fault. This crustal fault has a steep (nearly vertical) fault plane, and is supposed to be the causative fault of the Sanhe Pinggu M 8 0 earthquake. The two profiles respectively reveal the existence of a local strong reflectivity in the lower crust and the lower part of the upper crust, which is assumed to be a dike or rock mass formed by the upwelling and cooling down of materials from the upper mantle. Magmatic activity in this part brought about differences in local stress distribution, which then gave rise to the formation of the crustal deep fault. That may be regarded as the deep structural setting for the Sanhe Pinggu M 8 0 earthquake.更多还原