深地震测深揭示的济阳坳陷地壳结构特征

Crustal Structure Features of Jiyang Depression as Revealed by DSS Profiles

对穿过济阳坳陷的3条深地震测深剖面进行解释、对比分析显示,济阳坳陷地壳结构分为上、中、下3层,莫霍面深度在31km左右,区域起伏变化不大,深浅部构造呈镜像对称关系。济阳坳陷内中地壳存在低速体发育,为其顶面滑脱层的发育以及滑脱构造的形成提供了必要条件,也导致上下地壳厚度的横向变化存在差异。惠民凹陷下方P_m震相之前出现P_4震相表明,其莫霍面以壳幔过渡带形式存在;东营凹陷下方P_m震相尖锐,其莫霍面则表现为一级间断面性质,体现了不同凹陷深部壳幔作用的差异。结论表明,济阳坳陷地壳结构具有典型的华北地区地壳结构特征,上下地壳厚度横向变化差异与滑脱构造密切相关,而莫霍面性质差异与深部软流圈上涌以及下地壳小规模拆沉有关。

Through processing and contrast analysis of 3 deep seismic sounding lines crossing Jiyang depres- sion, we find that the crustal structure of Jiyang depression can be divided into three layers： upper, mid and lower crust. The Moho depth of Jiyang depression is about 31 km, and the interface variation is gentle. The deep tectonic is mirror symmetrical to the shallow tectonic. Low velocity bodies exist in the mid-crust of Jiy- ang depression, providing necessary conditions for the detachment development, and causing variations of crustallateral thickness between the upper crust and lower crust. The Moho interface feature differs between the Huimin sag and Dongying sag. In Huimin sag there is a P4 seismic phase before the Pm phase, which is the reflection of the crust-mantle transition zone. However, in Dongying sag the Pm seismic phase reflects the features of first order discontinuous interface. The result shows that the crustal structure of Jiyang depression has typical features of north China and that asthenospheric upwelling changes the Moho interface property of Jiyang depression.