北京平原区断裂构造重力异常识别研究

区域重力异常蕴含丰富的断裂构造特征信息.采用小波多尺度分解、归一化总水平导数垂向导数(NVDR_THDR)和剖面2.5D重力异常反演方法对北京平原区高精度区域重力资料进行了处理,获得了主要断裂构造平面位置、长度、规模、汇交关系及深浅延伸特征,分析了利用重力异常识别断裂的效果.结果表明:(1)北京平原区NE向断裂平面延展长度大、连续性强,NW向断裂分段性明显,连续性弱,但NW向断裂对NE向断裂有切割改造迹象.近EW或SN向断裂分布较为局限.(2)主控断裂平面和垂向延伸特征差异明显,顺义断裂、孙河断裂、永定河断裂等为盖层断裂;南口断裂、孙河断裂西段、二十里长山断裂和张喜庄断裂为基底断裂;黄庄—高丽营断裂南段、南苑—通县断裂、礼贤断裂、夏垫断裂和皮各庄断裂东段为地壳断裂.(3)利用NVDR_THDR峰值异常带的连续性、幅值、宽度及错切关系可有效识别断裂的平面展布特征,通过小波变换获得的不同深度等效层异常结合2.5D剖面反演可有效研究断裂在基岩内部的深浅延伸情况,但重力异常的垂向分辨能力弱,断裂在新生界内部延伸特征需结合其他地质资料进一步分析.

Research on the faults identification based on gravity anomaly in Beijing plain

Abundant information of fault characteristic can be interpreted according to regional gravity anomaly data.The high-precision regional gravity data in Beijing plain are analyzed by multi-scale wavelet,normalized vertical derivative of the total horizontal derivative(NVDR_THDR)and 2.5D inversion of gravity anomaly method.The information about distribution,length,scale,intersection relationship and deep-shallow extension characteristics of faults is obtained,and the accuracy of results is contrasted and analyzed.The results show that:(1)the extension and continuity of NE-trending faults are well,however,the NW-trending faults are discontinuous with obvious segmentation feature in the Beijing plain.It′s worth noting that some NW-trending faults cut NE-trending faults.The EW or SN trending faults are relatively rare.(2)The main faults have obvious different characteristics in plane and vertical extension.The Shunyi fault,Sunhe fault and Yongdinghe fault are capping faults.Nankou fault and Ershilichangshan fault are basement faults.The southern section of Huangzhuang-Gaoliying fault,Nanyuan-Tongxian fault,Lixian fault,Xiadian fault,Zhangxizhuang fault and the eastern section of Pigezhuang fault are crustal faults.(3)By analyzing the continuity,amplitude,width and miscutting relation of NVDR_THDR peak abnormal band,the plane distribution characteristics of faults can be effectively identified.By analyzing the anomalies of equivalent layers at different depths obtained by wavelet transform and combining with 2.5D profile inversion,the information of faults extension inside bedrock can be insightfully revealed.However,due to the weak vertical resolution of gravity anomaly,faults extension in the inner Cenozoic should be further analyzed by combining with other geological data.