渭河盆地及邻区重力异常小波多尺度分解与解释

Multi-scale Wavelet Decomposition and Interpretation of Gravity Anomalies in the Weihe Basin and Its Adjacent Areas

基于EGM2008重力场模型计算获得了渭河盆地及邻区布格重力异常。采用小波多尺度分解方法对布格重力异常进行了4阶小波逼近和小波细节分解,同时基于平均径向对数功率谱方法定量化地计算出1~4阶小波细节和小波逼近所对应的场源平均埋深。结合区域地质和地震资料,对获得的重力场结果进行分析,得到如下结论:①鄂尔多斯地块、渭河盆地、秦岭造山带3个一级构造单元的布格重力异常之间存在明显差异;构造区内部重力异常也存在横向的显著差异。布格重力异常的走向、规模、分布特征与二级构造区及主要的断裂具有一定的对应关系。②渭河盆地及邻区布格重力异常1~4阶细节对应4~23 km不同深度的场源信息,鄂尔多斯地块南缘东、西部的地壳结构存在明显的差异;渭河盆地凹陷、凸起构造区边界清晰,断裂边界与重力异常边界具有较好的一致性;秦岭造山带重力异常连贯性不好,东、西部重力异常变化特征表现出明显的差异。③渭河盆地及邻区布格重力异常分布与莫霍面埋深具有非常明显的镜像关系。渭河盆地及邻区地震主要分布在六盘山—陇县—宝鸡断裂带、渭河断裂与渭南塬前断裂交汇处、韩城断裂与双泉—临猗断裂交汇处。渭河盆地及邻区重力异常主要由中上地壳剩余密度体所影响,这可能是该区地震以浅源地震为主的主要原因。

Based on the EGM2008 gravity field model,we obtain the Bouguer gravity anomalies in the Weihe Basin and its adjacent areas.And using the wavelet multi-scale decomposition method we decompose the Bouguer gravity anomalies to 4-order wavelet approximation and details.Based on the average,radial,ogarithmic power spectrum,we calculate the average depth of the field source corresponding to 1st,2nd,3rd,and 4th order wavelet approximation and details.Then we analyze the obtaine gravity field on the baiss of the regional geological and seismic data,and get the following conclusions:①The Bouguer gravity anomalies in first-order tectonic units,the Ordos block,the Weihe basin,and the Qinling orogenic belt,are obviously different,and the Bouguer gravity anomalies within each tectonic unit are horizontally different.The trend,scale,and distribution of the Bouguer gravity anomalies correspond with the secondary structural regions and the major faults in the research areas.②The 1st to 4th-order details of the Bouguer gravity anomaly in the Weihe basin and its adjacent areas correspond to the field source information at depths between 4 km and 23 km.The details of the Bouguer gravity anomaly at different orders reveal the following crustal structure features:The crustal structure in the east and west of the southern margin of the Ordos block is obviously different;The boundaries of sags and uplifts in the Weihe Basin are clear and the fault's boundaries are consistent with the gravity anomaly boundaries;The continuity of gravity anomalies in the Qinling orogenic belt is poor,and the variation characteristics of gravity anomalies in the east region are obviously different with those in the west.③The distribution of the Bouguer gravity anomalies in the Weihe Basin and its adjacent areas has a clear mirror-image relation with the Moho depth.The earthquakes in the Weihe Basin and its adjacent areas mainly occur in the Liupanshan-Longxian-Baoji fault zone,at the intersection of the Weihe fault and the Weinan Yuanqian fault,and at the intersection of the Hancheng fault and the Shuangquan-Linyi fault.In addition,the gravity anomalies in the Weihe basin and its adjacent areas are mainly affected by the residual density of the middle and upper crust,which may be the reason why the shallow-focus earthquakes are prone to occur in this area.