中文摘要：

郯庐断裂带（郯城～庐江断裂带）中段地震活动强度大、频率高，是中国东部一条重要的地震活动带。强震沿该断裂带中段局部发生，弱震不均匀分布，一些部位为无震区。本文利用5条大地电磁测深剖面，对该断裂带中段地震孕育的深部背景进行了对比分析。结果表明，该断裂带切穿整个地壳，地壳电性结构显著不均一，但普遍出现陡立的低阻带与高阻带相间排列的现象，从而成为强烈的新构造活动带。该断裂带上3处≥Ms7级强震的地壳电性结构实例显示，带内上地壳中、下部出现刚性高阻层连接旁侧或两侧刚性高阻体时才会出现大的应力积累，从而成为强震发生必要的深部结构条件。而该断裂带弱震区显示全地壳尺度陡立软弱低阻带与刚性高阻带相间排列现象，其中的高阻带内只能积累有限应力而诱发弱震。该断裂带无震区上地壳出现了巨厚的异常软弱低阻层，成为极易蠕滑带，旁侧的刚性高阻体完全无法积累应力而诱发地震。上述实际对比分析表明，大型活动断裂带内上地壳的电性结构和流变学与地震活动性密切关联。

英文摘要：

Strong and frequent earthquake activities makes the central segment of the Tan-Lu Fault Zone （Tancheng--Lujiang Fault Zone） become an important seismic belt in eastern China. The fault zone shows local strong earthquakes, inhomogeneous distribution of weak earthquakes and the presence of non-earthquake parts. On the basis of five magnetotelluric sections, comparison analyses are made for deep background triggering earthquakes in the central segment of the fault zone in this text. The results indicate that the fault zone cuts through the whole crust and shows highly heterogeneous crust textures. The common presence of alternation of steeply low- and high- resistivity zones in the crust sections leads intense neotectonic activities along the fault zone. Three examples of crust electrical textures for I〉 Ms 7 earthquakes in the fault zone reveal that the strong earthquakes occurred when middle and lower parts of upper crust have a rigid, high-resistivity layer connecting a rigid high-resistivity zone on one side or two rigid zones on both sides. In this case, the large, connecting rigid high-resistivity zone can accumulate big stress and trigger a strong earthquake. Weak earthquake regions in the fault zone show alternation of steeply soft low-resistivity and rigid high-resistivity zones, and the latter can accumulate limited stress and lead to weak earthquakes. Aseismic regions in the fault zone correspond to the presence of an extremely thick, soft low- resistivity layer that becomes a totally creeping zone. In this case, a rigid high-resistivity zone by the side of the extremely soft low-resistivity layer is difficult to accumulate any stress and cannot cause any earthquakes. The above comparison analyses suggest that seismic activities along a large active fault zone are closely related to its upper ernst electrical texture and theology.