ACTIVITY OF CENTRAL SEGMENT,CHANGDE-YIYANG- CHANGSHAN FAULT AT THE SOUTHERN MARGIN OF DONGTING BASIN,HUNAN,CHINA

doi:10.3969/j.issn.0253-4967.2011.04.009

Abstract

Abstract:

According to the detailed shallow geophysical survey,drilling,dating,geological geomorphic investigation along the central segment of the Changde-Yiyang-Changshan Fault at the southern margin of Dongting Basin,features about its geometry,dynamics,active epochs and basin structural type are revealed.The central segment of the Changde-Yiyang-Changshan Fault(buried fault),a normal fault,dips to NNE.It not only offset the Eogene top boundary,but also displaced the Huatian group(Q_p¹ht),Miluo group(Q_p¹m)of Lower-Pleistocene and Xinkaipu group(Q_p²x)of lower section of Middle-Pleistocene.The Baishajing group(Q_p²b)in the middle section of Middle-Pleistocene overlays the fault without any deformation and disruption.The latest active age is the early Pleistocene,but no active evidences after the mid-late Pleistocene are found.Vertical displacement of the top of basal rock(or bottom of Lower Pleistocene),that is, the total offset at the Quaternary,is 16.10m,but it becomes smaller towards the surface.The fault was coetaneous with the sedimentation of Huatian group(Q_p¹ht)and Miluo(Q_p¹1m).Based on the comparison of fault-controlled subsidence and sediment thickness,it can be concluded that the Anxiang-Hanshou depression was formed mainly by deformation,not by faulting.Both faults and moderate earthquakes are concentrated along the zones between Dongting Basin and surrounding uplifting mountains.It can be looked as an important evidence for determining the seismotectonics of moderate earthquake,whether a fault offsets the lower or middle Pleistocene.

Key words: Dongting Basin, central segment of Changde-Yiyang-Changshan Fault, basin structure type, seismotectonics of moderate earthquake

摘要：

通过对洞庭盆地南缘常德-益阳-长沙断裂中段较为详细的浅层物探、钻探、年代学测试以及地表地质地貌调查和综合分析等方面的工作,获得了一些新的认识: 常德-益阳-长沙断裂中段(隐伏断裂)表现为一条倾向NNE的正断裂,断错了古近纪基岩顶界面,并向上切错下更新统的华田组(Q_p¹ht)、汩罗组(Q_p¹m)和中更新统下段新开铺组(Q_p²x)底界面,而中更新统中段的白砂井组(Q_p²b)则平整地覆盖在断裂之上,无任何变形和位错形迹。断裂的最新活动时代在中更新世早期,中更新世中晚期以来已无活动迹象。断裂两盘基岩顶界面(或下更新统底界面)垂直落差(即第四纪以来总断距)为16.10m;越往上断距越小。同一层位,断层上盘的华田组(Q_p¹ht)和汩罗组(Q_p¹m)的沉积厚度远大于断层下盘的沉积厚度,表明该断裂的活动具有较多的边沉边断的同生性质。以与洞庭盆地南缘常德-益阳-长沙断裂中段对应的安乡-汉寿凹陷为例,通过对第四纪以来断裂控制的差异性沉降幅度与凹陷内沉积厚度的对比分析,初步认为安乡-汉寿凹陷主要是通过拗陷作用形成的,而不是断陷作用。洞庭盆地与周边隆起山地之间不但断裂发育,同时也是中强地震集中发生的地带。一条断裂是否存在断错早、中更新世地层的构造现象,是判断中强地震发震构造的一个重要标志。

关键词: 洞庭盆地, 常德-益阳-长沙断裂中段, 盆地构造属性, 中强地震构造

CLC Number:

P315.2

HAN Zhu-jun, XIANG Hong-fa, JI Ji-fa. ACTIVITY OF CENTRAL SEGMENT,CHANGDE-YIYANG- CHANGSHAN FAULT AT THE SOUTHERN MARGIN OF DONGTING BASIN,HUNAN,CHINA[J]. SEISMOLOGY AND GEOLOGY, 2011, 33(4): 839-854.

韩竹军, 向宏发, 姬计法. 洞庭盆地南缘常德-益阳-长沙断裂中段活动性研究[J]. 地震地质, 2011, 33(4): 839-854.

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