文中推导并给出了基于非格网分布的起伏面扰动重力或重力异常解算区域扰动重力梯度场模型的数值计算公式.基于澳大利亚 West Arnhem Land 地区的格网重力数据,以频谱域(二维快速傅里叶变换)解算的扰动重力梯度全张量作为"基准值",然后利用基于推导公式的最小二乘配置方法(LSC)对相同区域非规则范围的重力数据进行扰动重力梯度模型解算,将结果作为"评估值".对比"基准值"与"评估值"之差,研究发现:1)基于推导公式的最小二乘配置方法解算得到的扰动重力梯度值与频谱域方法得到扰动梯度"基准值"各分量在空间形变变化上是一致的;2)统计扰动重力梯度各分量的差值 ΔδΓfft-lscxx、ΔδΓfft-lscxy、ΔδΓfft-lscxz、ΔδΓfft-lscyy、ΔδΓfft-lscyz 和 ΔΓfft-lsczz,"基准值"与"评估值"差值的标准差分别为 5.54E、5.30E、1.85E、6.55E、2.09E 和 9.67E(1 E=1×10-9s-2),远低于国际上实测重力梯度与解算模型差值的研究结果.最后,基于云南地区实测地表差分重力值,文中首次给出了该区域半波长约 20km的重力梯度场年际变化模型.文中的思路和方法提高了广泛分布的重力数据(主要为重力异常和扰动重力)的使用效率,可为地球物理学、地质学研究更好地理解和解释重力数据、重力梯度数据及其与场源的关系提供数据基础.

针对在陆地百千米以上的时变流动重力观测网络中,相对重力仪非线性漂移率和仪器性能偏差是影响观测结果精度的主要误差来源这一问题,以1990-2022年云南流动重力观测数据为例,对比传统最小二乘平差方法和贝叶斯平差方法得到的非线性漂移率结果,系统测评了贝叶斯估计方法对于提高重力平差结果精度的有效性.结果表明,可以通过贝叶斯优化方法给出合适的仪器权重和非线性漂移率,减少多台相对重力仪性能差异造成的误差和传统线性漂移计算方法造成的有效漂移遗失,提高平差结果的精度.

文中基于滇西地震实验场1986—2014年间近30a的流动重力观测资料,研究了该地区重力场的长期变化背景.结果表明,重力场长期变化背景以负变化为主,年平均变化率约为-1.24×10-8 m/s2;空间分布上,重力场变化的剧烈程度与断裂带分布和历史强震活动存在密切关联,红河断裂北段、龙蟠-乔后断裂对本地区的重力场变化和地震活动分布具有明显的边界作用.结合地壳垂直形变、地壳结构和区域动力学背景对重力场变化机理进行分析,重力场整体负变化趋势可能反映下地壳物质流引起的地表隆升和地壳增厚,而重力场变化空间分布的细节则与区域动力学背景下具体断裂带的活动特性以及相关的局部性物质分布变化有关.

时变重力信号能反映地球内部介质迁移引起的不均衡变化,本文利用三维欧拉反褶积方法,通过建立合适的场源模型获得最佳反演参数,并采用水平梯度滤波法消除部分虚假发散解,优化反演结果.在此基础上,利用川滇地区2015-2019年流动重力重复观测资料,分析了不同时空尺度的区域重力场动态变化特征,开展对川滇地区重力变化场源特征的定性和定量研究.结果表明:欧拉反褶积方法能有效反演重力场变化异常的场源三维空间分布特征,反演结果与2018年12月16日四川兴文县Ms5.7地震,2019年6月17日长宁县Ms6.0地震及同年7月4日珙县发生的Ms5.6地震位置相对应,揭示了区域内的构造活动特征,为地表时变重力数据的反演和解释提供了思路和方法,同时也对捕捉与深部构造相关的地震前兆信息、开展强震中长期预测的应用研究具有现实意义.

The terrestrial time-variable microgravity survey is an important means to monitor geodynamic processes underground. The Scintrex CG-5 relative gravimeter, which is the mainstream instrument for terrestrial relative gravity measurement at present, its scale factor (SF) is an important factor affecting the quality of the observation data. Unlike the conventional gravity adjustment procedure, this study takes account of the nonlinear drift rate of the CG-5 gravimeter, depending on the known absolute gravity (AG) in the network, and the scale factor is considered as one of the hyper-parameters to be estimated by means of Akaike’s Bayesian information Criterion (ABIC). In order to quantify the errors caused by the bias of scale factor, we applied this new approach to process actual gravity survey campaign data in Yunnan gravity network from 2018 to 2020, then analyzed the residuals of gravity differences (GD) between station pairs and the difference of GD between two relative gravimeters (CG5 #1169 and CG5 #1170). The cross-validation of the absolute gravity (AG) from the quasi-synchronous observation in the network is also used in the paper. It has shown that this new approach is effective to improve the accuracy of scale factor and adjustment results.

文中对云南省区域范围内的2015—2021年的相对重力数据进行了平差计算,结合区域地质构造环境和区域范围内已发生的地震震例,系统分析了区域重力场变化和地壳水平运动的时空分布特征,获得了区域重力场变化与漾濞MS 6.4地震之间的关系.结果表明:1)2018—2021年震中位置的重力变化较弱,以震中为中心,附近区域在短期及1 a期、2a期和4a期基本呈四象限特征且重力变化较为剧烈;2)震前短期及多年期重力变化显示,重力场高梯度带集中在漾濞—下关区域,且零值线交替出现在该区域;3)震前多年期重力变化显示,发震断裂带南涧-巍山断层的西侧重力呈负变化、东侧重力呈正变化,该地震为包含走滑分量的正断型地震,与全球台网数据的计算结果一致;4)对临震1a期重力变化异常指标进行了分析,发现重力转折变化异常的量级为75×10-8m·s-2,重力变化异常时变距约为130km.漾濞地震的实际震级MS 6.4稍大于重力异常指标公式的计算结果MS 6.2,且震后漾濞地区相继发生了42次MS>3.0地震,可判断出漾濞地区地下活动能量已完全释放,MS 6.4地震为此处地震序列的主震,主震后短期内无更大地震发生.

利用京津冀地区2018—2020年5月的流动重力观测资料,分析了2020年7月12日河北唐山古冶5.1级地震前不同时间尺度重力场变化.结果表明:0.5年尺度重力场变化图像较好地反映了此次地震"震前一年,重力场持续上升(正)变化→震前反向变化→在重力变化梯度带零等值线附近发震"的演化过程;震前0.5年和1年年尺度重力场均显示,地震发生在重力变化零等值线附近.

Multidisciplinary research shows the Red river fault zone’s (RRFZ) present movement and deformation state has complex segmentation feature. In order to further reveal its deep deformation mode, firstly, we extract tectonic movement gravity change information from mobile gravity measurement data by remove water storage varation and Vertical movement gravity effect; Secondly, together crust density interfaces model with gravity change information, then we can get the NMRFZ’s deformation mode of deep crust, which causes gravity variation.The average effect with a 50km radius is calculated for the recent gravity change rate in the Sichuan-Yunnan region, then the background rate field and the residual gravity change rate field are obtained. The trend of -0.66μGal/yr gravity-low-speed change in Sichuan-Yunnan region indicates that there is an inheritance between the gravity field and the uplifting background of the southeastern Tibetan Plateau. The crustal uplift is an important reason for the negative surface gravity changes, but it is mainly related to the deep tectonic environment. There are local positive change zones in the block boundary area, with obvious lateral extrusion and deep mass accumulation. It reflects that under the dynamic environment of the eastward flow of the Tibetan Plateau, the crust of north and middle-south section of the RRFZ are extruded and the underground mass become densification which make the surface gravity raising. The positive gravity changes in up-middle crust are more obvious than lower crust and Moho in Sichuan-Yunnan area. The RRFZ also exhibits a strong demarcation feature as a plate boundary, and the northern segment is the dividing line of gravity positive and negative changes area, while the middle-southern segment and its two sides also showed a wide range of positive change trends, with deep mass continue accumulation.The results of crustal deep deformation show that both the upper and the lower crust are obviously demarcated along the 101.5°E boundary, with the west side of the southwest Yunnan descending (moho: -0.05m/yr, upper-middle crust: -0.03m/yr) and east side of Sichuan-Yunnan block rising (moho ： 0.05m/yr，upper-middle crust： 0.02m/yr), which shows that the control effects in depth of the Kangdian crustal axis. The deformation rate of the deep crust in the RRFZ is the largest, the middle-south is next and the south the smallest. Gradual zone between the middle-south segment of the RRFZ and the Chuxiong-Jianshui fault zone shows strong activity and difference in the upper middle crust.

采用线性回归方法分析2015-2018年云南区域内相对重力观测数据,分析获取到的云南省2台CG-5相对重力仪3年内一次项系数变化差异,发现段差与互差呈线性关系;利用线性回归方法获取3年内每个观测周期的一次项系数,结合绝对重力点资料,对得出的一次项系数进行验证;对比一次项系数修正前后3年期的变化趋势,分析重力变化与2018年地震相关性.结果 表明:2台CG-5重力仪一次项系数在3年内均发生变化,且变化规律不一致,一次项系数变化差异最大达到0.0002;在一个观测周期内,一次项系数随时间及测值段均未发生明显变化;一次项系数修正前后对重力观测数据最大影响能达到100×10-8 m/s2以上,且修正后的数据与绝对重力观测值符合性更好,与地震的相关性也更加明显.

Using the gravity remeasurement data from 2011 to 2014 in the Sichuan-Yunnan region, We have systematically analyzed the spatial-temporal variations of the regional gravity field and their relation to the occurrence of the Yiliang M(S)5. 7 earthquake in 2012, Lushan M(S)7.0 earthquake in 2013, Ludian M(S)6. 5 earthquake and Kangding M(S)6. 3 earthquake in 2014. Combined with GPS data and leveling observations and regional geologic structure, the time-space distribution of the gravity field and its mechanism were further studied, and its implication for seismic risk is discussed. The interannual variation of gravity dynamic change in the Sichuan-Yunnan region during 2011 to 2012, 2012 to 2013, 2013 to 2014 and the accumulation change during 2011 to 2014 are analyzed. And we have discussed the evolution characters of the gravity field. Combined with regional gravity field variation and seismic activity, and with GPS data during 2011 to 2014, and leveling data during 1971 to 2011, we have found the relationship between strong earthquake and gravity variation in recent years. And on this basis, combined with regional geology structure, we further assess the seismic risk in the Sichuan-Yunnan region in the future. The results show that gravity variation is closely linked with the fault activity in the Sichuan-Yunnan region. It is caused by material migration accompanying active faulting and crustal tectonic motion. The gravity data from the survey area since 2012 have obvious response to four major earthquakes (M-S>5. 7). Regional gravity anomalies and a gravity gradient change may be a seismic precursor. Dynamic evolution characteristics of the gravitational field roughly reflects the dynamic effects of the moving material of the Tibetan plateau which spread toward east and the Longmenshan fault zone by the crust uplift, where compression rates and gravity change are most significant. The spatial distribution of the gravity field and its changes over time and vertical and horizontal crustal movement and tectonic activity observations have certain corresponding relationships. To utilize the remeasurement data to regional gravity change, we have researched its relationship with seismic activity. Gravity dynamic variation has important implications for location prediction of earthquakes, providing experience and reference for medium-term forecast. Earthquakes are easy to occur in four quadrant distribution centers of gravity change or high gradient belts of positive and negative anomalies. Some areas of gravity anomalies have medium-long term seismic risk.

The August 3, 2014, Ludian, Yunnan, M(s)6.5 earthquake which focal mechanism is the left-lateral slip. The rupture surface of earthquake is the NW direction and almost perpendicular to Zhaotong fault. In our study, we used the 3D gravity inversion approach to inverse 3D density structure, and made a high-quality reference model as initial model with the Crust 1.0 and the newest Moho relief derived by ChinArray project. The 3D density structure shows that the block movement located at the south and north part of Ludian earthquake had been resisted by the Zhaotong fault (ZTF) in the geological time scale, respectively. The resisted ability of north part ZTF is stronger than the south part. Furthermore, we found the significance decrease of gravity field at the Dahaichun (P1) from Oct. 2012 to Jun. 2014. But the gravity change of Jiangdi (P5) measurement point shows the increase tendency. The significant gravity change can't be found at the other points. At last, we give a seismogenic model by the gravity approach. Our results are very important to understand the deep structure of seismogenic region, and also like the key to find the seismic precursor which related to the local gravity change.