Optimizing the dataset size of a topo-bathymetric survey for Hammam Debagh Dam,Algeria

The capacity of water reservoirs may be considerably reduced by sediment transport and accumulation. This phenomenon may occur quickly in regions prone to erosion, such as Hammam Debagh Dam region in Algeria. For better management of water resources, it is important to estimate the volume of a reservoir by regular and frequent topo-bathymetric surveys. Topo-bathymetric surveys with a high point measurement density are expensive and time-consuming. To reduce this expense and to increase the frequency of topo-bathymetric surveys, it is required to optimize their size and density. The complete survey of the reservoir created by the Hammam Debagh Dam in Algeria was examined in comparison with 19 reduction subsets using geostatistics. The study showed that the complete dataset of 32,164 points, corresponding to a density of 42 points ha^-1 could be reduced to 10,000 points, i.e. 13 points ha^-1, without affecting the estimation of the water volume in the reservoir. This reduction could considerably simplify the work load, reduce the expenses to do these surveys, and, therefore, allow for an increased frequency of topo-bathymetric surveys.     

大同市地裂缝三维断层形变测量值与辅助温度的相关分析

简要介绍同车公司地裂缝观测站情况,以2013年至2016年数字化改造后的观测数据为基础,结合仪器工作原理,分析三维断层形变测量仪测值与观测仪两端辅助温度测值的关系。结果表明,地裂缝三维断层形变观测中,垂直向DFG观测受地裂缝两端辅助温度影响较显著,地裂缝垂直形变变化是热形变效应和断层运动信息的综合反映。     

庐山重力基线场稳定性分析

利用2018年庐山重力短基线场绝对重力和相对重力观测资料,基于绝对重力控制下的相对重力联测方式对庐山基线场的稳定性进行了分析。结果表明：庐山基线场2015～2018年测段重力变化为-11.6～13.4μGal、均值-0.962μGal,较小的重力变化表明庐山短基线重力场较稳定;2000～2018年测段重力变化为-39～33.5μGal、均值-0.275μGal,总体以G16测点为界呈分化特征,上山侧（G16～JZ04）重力变化较平缓（约-3 μGal）,下山侧（G03～G16）因G04、G14测点重力值变化显著（分别为-24.95、-18.5μGal）,导致相邻测段重力变化剧烈;测段重力变化与段差比值（B）为1.19×10^-4～3.58×10^-3;庐山及其周边地区由地表垂直运动引起的重力变化速率为0.7543±0.16μGal/a;近期研究区地震活动性呈震级小、沿断裂带集中分布特征;重力变化对相对重力仪一次项系数标定结果影响较大（正比于B值）,对校正精度影响小,利用以往重力观测成果进行一次项系数标定时,绝对重力测段JZ02～JZ04误差影响小于最大重力段差测段,定期维护和复测是保障高精度重力短基线场的有效途径。     

Experimental study on frequency-dependent elastic properties of weakly consolidated marine sandstone: effects of partial saturation

Investigating seismic dispersion and attenuation characteristics of loosely compacted marine sandstone is essential in reconciling different geophysical measurements (surface seismic, well logging and ultrasonic) for better characterization of a shallow marine sandstone reservoir. We have experimented with a typical high-porosity and high-permeability sandstone sample, extracted from the Paleogene marine depositional setting in the Gulf of Mexico, at the low-frequency band (2–500 Hz) as well as ultrasonic point (10⁶ Hz), to investigate the effects of varying saturation levels on a rock's elasticity. The results suggest that the Young's modulus of the measured sample with adsorbed moisture at laboratory conditions (room temperature, 60%–90% humidity) exhibits dispersive behaviours. The extensional attenuation can be as high as 0.038, and the peak frequency occurs around 60 Hz. The extensional attenuation due to moisture adsorption can be dramatically mitigated with the increase of confining pressure. For partial saturation status, extensional attenuation increases as increasing water saturation by 79% with respect to the measured frequencies. Additionally, the results show that extensional attenuation at the fully water-saturated situation is even smaller than that at adsorbed moisture conditions. The Gassmann–Wood model can overall capture the P-wave velocity-saturation trend of measured data at seismic frequencies, demonstrating that the partially saturated unconsolidated sandstone at the measured seismic frequency range is prone to be in the relaxed status. Nevertheless, the ultrasonic velocities are significantly higher than the Gassmann–Wood predictions, suggesting that the rocks are in the unrelaxed status at the ultrasonic frequency range. The poroelastic modelling results based on the patchy saturation model also indicate that the characteristic frequency of the partially saturated sample is likely beyond the measured seismic frequency range.     

Elastic properties of sands,Part 1: Micro computed tomography image analysis of grain shapes and their relationship with microstructure

Elastic properties of an unconsolidated sand are largely dependent on the elastic properties of its constituent grain and the micro-structure that defines how the grains are arranged within themselves. Coordination number, that is the average number of contacts a grain has with its neighbours, and contact surface area are the two parameters closely related to the microstructure. Moreover, grain shapes and sorting also have substantial influence on these parameters. To calculate these parameters and find any potential relationships with the shape factors, we acquire high-resolution micro computed tomography images of four mechanically compacted unconsolidated dry sand samples that are of different shape factors and sorting indices. After a comprehensive voxel-based data processing, we calculate shape factors such as sphericity and roundness of each grain in all samples. Using own algorithm, we then calculate the coordination number and contact surface area. Results show that samples of well-sorted and higher spherical and rounded grains have higher coordination number and contact surface area than the samples of poorly sorted and lower spherical and rounded grains. Among the poorly sorted samples, coordination number is largely dependent on the fraction of larger grain sizes present in the sample. Inside any given sample, grains of lower sphericity tend to have higher coordination numbers. Moreover, more spherical and rounded grains have greater contact surface area with their neighbours.     

垂直形变趋势累计率在川滇地区的应用

本文在研究形变趋势累计率的基础之上,对数据处理方法进行了局部改进,将跨断层场地布设较多的川滇地区作为实验区,利用精密水准测量分析该地区的垂直形变异常强度,并结合川滇地区震例开展研究。分析发现强震发生前后一段时期,震中附近形变异常强度几乎保持一致,但在震前（1、2个月左右）会发生较大改变,震后逐步恢复到与震前相同的情况;强震主要发生在形变异常强度值变化较大区域附近。垂直形变趋势累计率在中短期的映震效果较好。     

岩石压应力传递系数计算及影响机制

钻孔应变观测是地壳岩石应变相对测量的主要方法,对其附加应力场的研究,可以有效分析岩石压应力向探头的传递过程,可对应变仪有关力学参数的设计和观测数据的物理解释提供帮助。考虑到外加应力在岩石、水泥和仪器钢筒等3层介质中传递的实际情况,根据弹性力学中的厚壁圆筒方程,推导轴对称应力作用下岩石压应力的传递系数公式,分析影响机制,并给出有关变化规律曲线和定量指标。     

复测水准网动态平差及其在川滇地区垂直地壳形变中的应用

以1995—2016年川滇地区实测水准资料为例,分别采用动态经典平差、拟稳平差、伪逆平差和GPS速率约束平差4种平差方法进行平差计算,分析探讨4种平差方法在水准网平差处理时的适用条件及优缺点;最后分析了1995—2016年川滇地区的地壳垂直形变特征。结果表明:①在条件具备的情况下,GPS速率约束平差优于动态经典平差、拟稳平差和伪逆平差,主要体现在GPS速率可知、平差后速率误差明显减小,且能有效地抑制误差的传播与积累;而拟稳平差、伪逆平差虽优于动态经典平差,但同样存在着基准假定的问题;②1995—2016年川滇地区整体处于差异隆升阶段,只有四川盆地、滇西北和滇南少部分区域下沉,跨断裂剖面结果显示几条断裂带以继承性运动为主。     

加速度计及其融合高采样GNSS的低频信号测量特性研究

搭建了一套振动台系统,模拟不同频率振动信号对加速度计进行测试,并从信号功率谱密度和积分位移2个方面对其低频测量特性进行分析。实验表明,当振动信号频率高于0.05 Hz时,对加速度计信号进行高通滤波并积分能够恢复出较准确的振动位移;反之,随着信号频率的降低,积分位移误差增大。因此,为解决加速度计低频测量能力不足的问题,利用高采样GNSS与加速度计数据融合的方法,成功恢复了极低频振动信号。研究表明,振动台系统能够为地震监测研究提供良好的基础平台;加速度计准确恢复位移信号的低频下限在003~0.05 Hz左右,研究方法及结果可为加速度计频带的合理选择提供参考;同时,利用高采样GNSS与加速度计融合方法能够有效弥补加速度计低频测量能力不足的缺点,使地震低频位移更加准确可靠。     

GB-SAR变形监测技术研究现状与展望

地基合成孔径雷达（GB-SAR）技术是近十多年发展起来的地面主动微波遥感技术,可进行非接触、高精度、大范围、远距离的变形监测,在变形监测领域具有重要意义。本文首先介绍了GB-SAR干涉测量基础理论和研究现状,归纳了目前主要的GB-SAR系统,详细列举了现有系统的关键参数;进而分析了GB-SAR技术在基础设施、滑坡、矿山、冰川运动及文物保护等变形监测领域应用的优势和不足,总结了地基雷达系统在实际应用中面临的挑战;最后从多维形变、大气改正等方面对其应用前景进行了展望。