高密度电法探测第四纪玄武岩覆盖区断裂及其活动性分析——以鸭绿江断裂带抚松段西支断裂为例

Detecting Active Faults in Quaternary Basalt Areas by the High-Density Electrical Method:An Example of the West Branch of the Fusong Section of Yalüjiang Fault Zone in Northeast China

覆盖区活动断裂探测往往需要选择合理的物探方法以确定断裂位置,高密度电法具有数据采集效率高、探测精度高等优点,已在覆盖区活动断裂探测中得到广泛应用。本文利用高密度电法在长白山玄武岩覆盖区进行断裂探测,对实测数据进行反演,分析了NE向鸭绿江断裂带抚松段西支断裂在松江河镇北东侧第二松花江畔的展布形态,同时,利用钻探对断裂探测结果加以验证。视电阻率剖面表明完整基岩主要呈现出高阻值,断裂破碎带由于含水丰富则呈现为低视电阻率异常值。而断层内较为破碎,且富含水,故在视电阻率剖面上呈现明显低阻异常,这些结果能够与钻孔揭露地层实物资料较好对应。钻孔的断层样品^(14)C测年结果显示,西支断裂在松江河镇兴隆林场为晚更新世活动断裂。

Detection of active faults in coverage areas requires the selection of proper geophysical methods to determine the location of fault.The high-density electrical method with the advantages of high efficiency in data acquisition and high detection accuracy has been widely used in the detection of active faults in such areas.In this work the high-density electrical method was employed to detect the faults in the basalt area of the Changbaishan Mountains.The measured data were inverted to analyze the distribution pattern of the west branch of the Fusong segment of the NE-trending Yalüjiang river fault zone along the second Songhua River in the northeast of Songjianghe Town.At the same time,the fault detected was verified by drilling.The apparent resistivity profile shows that the intact bedrock mainly exhibits high resistance values,and the fractured zone of the fault presents low apparent resistivity anomalies due to its rich water content.The interior of the fault is relatively broken and rich in water,so its obvious low-resistivity anomalies appear in the apparent resistivity profile.These results corresponded well to the formation revealed by the boreholes.The ^(14)C dating on the fault samples from the boreholes shows that the west branch of the fault was active in the Late Pleistocene in the Xinglong forest farm of Songjianghe Town.