漳州台深井综合观测与洞体应变观测资料对比分析

根据漳州地震台深井观测系统中探头上、下端面共8分量应变观测单元及台站洞体内伸缩仪的应变固体潮观测资料,利用相互垂直的一对线应变分量共5种组合的方式计算出本地的面应变,并与固体潮理论值进行两两相关分析比较。结果表明,深井观测系统的4种面应变组合的变化形态较伸缩仪面应变更接近固体潮面应变理论值,其中6#8#组合为最优组合,与固体潮理论值相关系数高达0．9418,而伸缩仪组合与理论值相差较大,相关系数仅为0．7838。Venedikov调和分析显示,深井观测系统的内在质量优于洞体内伸缩仪的观测质量。     

Strain variation with progressive deformation in basement-involved trishear structures

Basement-involved structures associated with reverse, vertical and normal faults commonly involve non-parallel shear within a triangular deformation (trishear) zone located on the front limbs of the structures. Deformation within the trishear zone is characterized by shear gradients and an associated decrease in the dips of the beds in stratigraphically higher units. Geometric models suggest that the layer-parallel strain within the trishear zone depends on the type of fault (normal, reverse, or vertical), the dip and throw of the fault, the dip of the anticlinal or synclinal axial surfaces, and the distance of any unit above the initial tip of the trishear zone, located at the basement-sediment contact. At any given location, reverse faults typically show increasing layer parallel shortening, followed by decreasing layer parallel shortening and a transition to extension, with increasing throw. The transition from contraction to extension occurs at lower values of throw for stratigraphically lower units and also for faults with smaller dips. Vertical and normal faults exhibit increasing layer-parallel extension of all units with increasing throw, with larger extension for stratigraphically lower units. Experimental models suggest that the trishear zone can expand with increasing fault throw. The strain within the trishear zones is accommodated largely by secondary faults, which are rotated with progressive deformation. The strain variations in the experiments closely mimic those predicted by the geometric models for reverse, vertical, and normal faults.     

海原形变观测资料异常分析

对海原台CZB-1型竖直摆钻孔倾斜仪记录到的地表倾斜方向的异常变化进行了分析,同时对该台YRY-4型分量应变仪依据自检方法表现出的压缩及伸张性异常进行了提取,得出以上两测项观测资料在宁夏南部发生的3次Ms3．0级以上有感地震的2次地震前出现了一定的异常信息,与地震赢救蚺蕴。     

Characterization of landslide ground surface kinematics from terrestrial laser scanning and strain field computation

Assessment and mitigation of the risk induced by landslide activation need an appropriate phenomenon investigation, to obtain useful information about the failure processes. The first step is the complete kinematics characterization of the landslide ground surface, by evaluating the involved displacement and deformation patterns. A dense displacement field can be obtained from comparison of a series of multi-temporal observations performed by means of terrestrial laser scanning. Subsequently, the strain field can be computed from displacement vectors. In this paper, a modified least square technique is employed to compute the strain on the nodes of a regular grid (2D approach) or on the points of a digital terrain model (3D approach). Such a computation takes into account the displacements, their spatial distribution, as well as the measurement and modelling errors. A scale factor is introduced in order to emphasize the contributions of the experimental points on the basis of their distance from each computation point, and to recognize possible scale-depending behaviours. This method has been implemented in Matlab and applied on two landslides located in the northeastern Italian Alps (Lamosano and Perarolo di Cadore). The experiments show that different kinematics can be recognized, and the presence and influence of eventual discontinuities can be revealed.     

Refined models of gravitational potential energy compared with stress and strain rate patterns in Iberia

This study examines the role of gravitational potential energy (GPE) in generating second-order (spatial scale ∼10² km) variations in the Iberia stress and strain-rate patterns. We present a new map of present-day strain rate field derived from the secular velocity field computed using all available continuously operating Global Navigation Satellite Systems (GNSS) stations in Iberia. The estimated strain rate field is generally consistent with the tectonic framework of the Iberian region, even though sporadic sharp local variations downgrade its correlation with the regional stress patterns. Many of the sharp spatial variations in the strain rate map are consistent with local changes of deformation style determined by prevailing faults. To obtain a more accurate estimate of GPE we use new data on the structure of the crust and apply a thin sheet approach using a 3-D definition of deviatoric stress. The GPE is derived from two isostatically compensated models (GPEd and GPEe compensated by density and elevation adjustment, respectively) and from the truncated geoid (GPEg). The GPE stresses are then summed with the first-order stress field due to the Eurasia–Nubia (EU–NU) convergence and the results compared with both the stress and strain rate data. In agreement with previous studies, we find that the GPE does not significantly change the NW–SE average direction of the most compressive stress (SHmax) imposed by the EU–NU collision, its main effect being to cause spatially changing stress regimes. From the analysis of the different GPE models we find: (1) in the Pyrenees, the tectonic forces have a secondary role when compared to the GPE. In this region, the model that best correlates with observations is the one emphasizing the role of surface elevation as a source of GPE (GPEe); (2) in the Iberian Chain and the Betics, the GPE imposes NE–SW extension consistent with a strike-slip regime and is equally (GPEe) or more (GPEg) important than the tectonic forces. In these regions, both deep heterogeneities associated with mantle convection and elevation are important sources of GPE; (3) in western Iberia, the GPE differences work against dominant tectonic forces by reducing the SHmax magnitude. The GPEg model is the one that best predicts the average strike-slip regime in Galicia; and finally (4) in the Gulf of Cadiz the gravitational potential stresses have a minor role and the style of deformation is clearly controlled by the tectonic forces.     

Modeling the strain localization around an underground gallery with a hydro-mechanical double scale model; effect of anisotropy

This paper concerns the application of a finite element squared approach for modelling hydromechanical coupling in the simulation of gallery excavation in the context of radioactive waste repositories. The micromechanics of Callovo-Oxfordian claystone is modelled at the microscale, taking into account the interaction of different mechanical constituents and its interaction with pore fluid. In a framework of computational homogenization, the micromechanical behaviour is coupled to the macroscale boundary value problem of a poromechanical continuum with local second gradient paradigm. The simulations concern several cases of the “Transverse action” benchmark by Andra, in the context of which the model is used.     

The strain seismograms of P- and S-waves of a local event recorded by four-gauge borehole strainmeter

At a sampling rate of 100 samples per second,the YRY-4 four-gauge borehole strainmeters(FGBS) are capable of recording transient strains caused by seismic waves such as P and S waves or strain seismograms. At such a high sampling rate, data from the YRY-4 strainmeters demonstrate fairly satisfactory self-consistency. The strain tensor seismograms demonstrate the senses of motion of P waves, that is, the type of seismic wave travels in the direction of the maximum normal strain change. The observed strain patterns of S waves significantly differ from those of P waves and should contain information about the source mechanism. Spectrum analysis shows that the strain seismograms are consistent with conventional broadband seismograms from the same site.     

Hydrogeochemical study in the Main Ethiopian Rift: new insights to the source and enrichment mechanism of fluoride

The central Main Ethiopian Rift suffers a severe water quality problem, characterized by an anomalously high fluoride (F) content that causes an endemic fluorosis disease. The current study, conducted in the Ziway–Shala lakes basin, indicates that the F content exceeds the permissible limit for drinking prescribed by the World Health Organization (WHO; 1.5 mg/l) in many important wells (up to 20 mg/l), with even more extreme F concentration in hot springs and alkaline lakes (up to 97 and 384 mg/l respectively). The groundwater and surface water from the highlands, typically characterized by low total dissolved solids (TDS) and Ca (Mg)–HCO₃ hydrochemical facies, do not show high F content. The subsequent interaction of these waters with the various rocks of the rift valley induces a general increase of the TDS, and a variation of the chemical signature towards Na–HCO₃ compositions, with a parallel enrichment of F. The interacting matrixes are mainly rhyolites consisting of volcanic glass and only rare F-bearing accessory minerals (such as alkali amphibole). Comparing the abundance and the composition of the glassy groundmass with other mineral phases, it appears that the former stores most of the total F budget. This glassy material is extremely reactive, and its weathering products (i.e. fluvio/volcano-lacustrine sediments) further concentrate the fluoride. The interaction of these “weathered/reworked” volcanic products with water and carbon dioxide at high pH causes the release of fluoride into the interacting water. This mainly occurs by a process of base-exchange softening with the neo-formed clay minerals (i.e. Ca–Mg uptake by the aquifer matrix, with release of Na into the groundwater). This is plausibly the main enrichment mechanism that explains the high F content of the local groundwater, as evidenced by positive correlation between F, pH, and Na, and inverse correlation between F and Ca (Mg). Saturation indices (SI) have been calculated (using PHREEQC-2) for the different water groups, highlighting that the studied waters are undersaturated in fluorite. In these conditions, fluoride cannot precipitate as CaF₂, and so mobilizes freely without forming other complexes. These results have important implications for the development of new exploitation strategies and accurate planning of new drilling sites. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

中国大陆及周边地区的水平应变场

推导并建立了块体的两种弹性运动方程：块体的整体旋转与均匀应变方程和块体的整体旋转与线性应变方程. 应用统计学原理,使用西域、青藏和华北块体上的GPS站速度数据,对这两种弹性运动方程与刚体运动方程模拟块体站速度的无偏性和有效性进行了统计检验. 检验结果表明,块体的整体旋转与线性应变方程是描述块体运动的最优模型. 将中国大陆划分为10个块体,应用块体的整体旋转与线性应变方程和块体上的GPS站速度估计了各个块体上的旋转与应变参数,按照1°×1°的间距计算了中国大陆及周边地区上1005个点的应变参数,分析了中国大陆及周边地区应变场的基本特征. 用本文方法得到的主压应变方向与地质学方法和测震学方法得到的主压应力轴方向具有很好的一致性(华南块体除外).     

充液井孔中的相控线阵声波辐射器在地层中产生的声场

应用有限元法研究了充液井孔中的相控线阵声波辐射器在井外地层中产生的声场,探讨了增强声源向地层的某一特定方向辐射的声波能量的方法. 采用相控线阵声波辐射器并调节其参数可以控制由充液井孔向地层中辐射的声波能量的方向,使声源向地层中的某个特定方向辐射的纵波能量得到明显提高. 在井间地震勘探和反射声波成像测井等领域中应用相控线阵声波辐射器,将有利于增大探测深度、提高探测分辨率和接收信号的信噪比.