郯庐断裂带白山—卅铺段第四纪以来的活动习性

QUATERNARY ACTIVITY OF THE BAISHAN SAPU SEGMENT OF THE TANCHENG-LUJIANG FAULT ZONE

根据构造地貌遥感解析,发现郯庐断裂带沿庐江白山到桐城卅铺一线显示1组平行断层,现场地震地质调查验证其为1组活动断层。通过断层剖面观测、样品采集及样品测试分析和宏微观构造分析,结果表明,郯庐断裂带在白山—卅铺一带第四纪以来仍具有黏滑、蠕滑交替的变形活动。其中,在柯坦—卅铺一带,最年轻的水系被NE向断层组右旋扭折,其断层物质的微观观测和测龄结果表明该断裂段第四纪时的活动具有脆、塑性过渡变形特征,强烈活动时间处于早、中更新世;而白山剖面断层泥年龄测试结果则反映相应断层段在中、晚更新世曾有过较强烈的活动。断层泥超微(SEM)和显微观测结果亦表明该断裂段曾发生黏滑、蠕滑交替的构造变形事件,且表现为先黏滑后蠕滑;结合水系呈现缓慢扭折表征,近年来沿断裂有不少微震发生,表明郯庐断裂带在白山—卅铺段的最新滑移方式主要表现为蠕滑,也就是说,该段积累的应力以蠕滑或微震等方式缓慢释放,据此推测未来一定时期内不易孕育强烈地震。

Remote sensing analysis of tectonic landforms revealed that the Baishan (Lujiang County) Sapu (Tancheng County) segment of the Tancheng Lujiang Fault zone appears as a series of parallel faults. Field investigation has confirmed that these parallel fault series are active fault. Moreover, in situ observation of fault profiles, as well as microstructural analysis of samples collected from the faults reveal that stick slip and creep slip deformation have occurred alternately along the Baishan Sapu segment of the Tancheng Lujiang fault zone since late Quaternary. In Ketan Sapu area, the youngest drainage system was dextrally offset by the NE trending faults. Microscopic observation and dating of the samples collected from the fault show that during Quaternary time the deformation along the fault was characterized by brittle ductile transition, and the strongest faulting event occurred in Early Middle Pleistocene. The dating results of fault gouges collected from Baishan profile indicate that this fault segment had been strongly active during Middle Upper Pleistocene. SEM and optical microscopic observations also show that stick slip and creep slip deformation had alternately occurred along this fault segment, and the stick slip deformation occurred earlier than the creep slip deformation. In consideration of the distortion of drainage system and the fact that minor earthquake occurred frequently along this fault segment in recent years, it can be postulated that the recent movement along the fault has been dominated mainly by creep slip, that is to say that the accumulated stress on this segment has been released slowly by creep slip or micro earthquake. Therefore, it is unlikely that a strong earthquake will occur on this fault segment in the near future.