Abstract: Bouguer gravity anomaly is a comprehensive reflection of deep and shallow density disturbances of the Earth’s internal mass. Important tectonic information of internal structure at different depths can be obtained by source separation of Bouguer gravity anomaly. Bouguer gravity anomaly from ground-based observations and Bouguer gravity anomaly from EGM2008 of the eastern Dabie Orogen were merged based on least-squares collocation. By model construction of massive bodies and data experiments, optimal wavelet base(sym6)and the corresponding optimal level(6)for gravity anomaly decomposition of the study area were confirmed. Two-dimensional discrete wavelet transform method was applied to obtain low-frequency components and high-frequency components of merged Bouguer gravity anomaly of the study area, and average depths of disturbed surfaces of the wavelet decomposition results were determined by spectrum analyses. In combination with data of crustal structure, geologic structure, effective elastic thickness of lithosphere and seismic activities, the deep structure and shallow structure of the crust were analyzed, and the structural background of seismic activities was discussed. The result shows that steep gradient belts of low-frequency components of Bouguer gravity anomaly outline the density transfer zones of deep structure between the eastern Dabie Orogen and surrounding blocks. It is speculated that the suture zone between the eastern Dabie Orogen and the North China Block locates at the front edge of Qingshan-Xiaotian Fault(the eastern part)and Meishan-Longhekou Fault(the western part), the structure transfer zone between the Dabie Orogen and the Yangtze Block locates at the Tancheng-Lujiang fault zone(the eastern part)and 20km north of Xiangfan-Guangji Fault(the southern part). The interior of the eastern Dabie Orogen is characterized by significant low gravity anomaly, which means an obvious depression of Moho surface, and the steep gradient belts of gravity anomaly inside the eastern Dabie Orogen indicate the imperfection of deep structure. High-frequency components of Bouguer gravity anomaly reveal that density structure of the mid-upper crust was influenced by regional faults such as Feizhong Falut, Lu’an-Hefei Fault, Meishan-Longhekou Fault and Tancheng-Lujiang fault zone. The distribution of high-frequency Bouguer gravity anomaly shows that Luo’erling-Tudiling Fault has obvious effect on density structure of the mid-upper crust, and the range of influence breaks northward through the NWW-orientated Qingshan-Xiaotian Fault and Meishan-Longhekou Fault, and may extend to the front edge of Feixi-Hanbaidu Fault. Further analysis combined with seismic activities shows that plate contaction occurred along the suture zones(front edge of Qingshan-Xiaotian Fault)of deep structure between the eastern Dabie Orogen and the North China Block. Besides, deep and shallow structures of this area are both imperfect, and not strong enough for long-time stress accumulation. Therefore, rocks tend to break at weak points(locations where faults intersect and shallow structure transfers)and release stress frequently, which are main reasons why small earthquakes concentrated at Huoshan area.

Key words: Bouguer gravity anomaly, wavelet analysis, tectonic features, Dabie Orogen

摘要： 文中通过多源数据融合、 模型构建、 数据试验、 二维离散小波变换和功率谱分析等方法获取了大别造山带东段深、 浅部场源布格异常及其场源似深度, 并结合地壳结构、 地质构造、 岩石圈有效弹性厚度和地震活动等资料, 讨论了地壳深、 浅部的结构特征及地震活动构造背景。 结果表明, 低频布格异常显示大别造山带东段与华北地块间深部构造缝合带在东部应位于青山-晓天断裂前缘, 在落儿岭-土地岭断裂和商城-麻城断裂之间向N偏移至梅山-龙河口断裂之下, 造山带南侧与扬子地块间深部构造缝合带位于襄樊-广济断裂以北约20km, 造山带东侧与扬子地块间的深部构造转换带位于郯庐断裂带之下, 造山带东段腹地显著的低频布格异常低值表明对应部位的莫霍面存在明显下凹, 造山带内部的布格异常高梯度带表明其深部结构不完整; 高频布格异常揭示肥中断裂、 六安-合肥断裂、 肥西-韩摆渡断裂和郯庐断裂带等主要断裂对地壳中上部密度结构的影响明显, 落儿岭-土地岭断裂对地壳中上部密度结构的影响范围向N延伸至肥西-韩摆渡断裂前缘。 结合地震活动资料进一步分析认为, 大别造山带东段与华北地块在青山-晓天断裂前缘附近接触和相互作用, 且大别造山带东段地壳深、 浅部结构均不完整, 不利于应力积累, 趋向于在断裂交错的脆弱部位频繁释放应力, 是霍山地区小地震活动频繁的主要原因。

关键词: 布格异常, 小波分析, 构造特征, 大别造山带