固体潮应变各向异性研究

钻孔应变仪的观测过程中发现潮汐应变响应存在方向各向异性, 推测是受到台站附近断层影响导致的。 我们对此展开数值模拟研究, 讨论软弱断层对潮汐变形传播的影响。 我们的研究结果证实了软弱断层的存在确实能够产生能够观测到的各向异性现象。 同时我们还发现其各向异性变化对断层弹性参数较为敏感。 观测到的部分地震震前反映固体潮应变各向异性的潮汐因子"玫瑰图"变化有可能是由于台站附近断层在震前的性质变化引起的。     

网格剖分及其精度和计算量分析

网格剖分程度直接影响着地震波正演数值模拟的计算精度及其计算量.以均匀介质模型为例,分析不同网格大小对波场模拟精度和计算量的影响,得出精细化网格剖分是实现高精度地震波正演模拟的有效方法,然而其计算量较大.以均匀倾斜介质模型为例,探讨倾斜地层网格剖分问题,数值实例分析不同震源频率对不同网格剖分方案引起的波场传播精度的影响,...     

裂隙弱度参数的波场特征

本文将Schoenberg线性滑移裂隙介质理论应用到HTI(LSD)介质的弹性波波场数值模拟之中.主要针对描述裂隙状态的2个裂隙参数——法向弱度EN和切向弱度ET对波场的影响进行了有限元模拟.模拟结果揭示了EN主要影响快波而ET主要影响慢波的波场特征,通过EN和ET变化对应的裂隙含水程度说明了EN对裂隙中的流体敏感而ET主要反映裂隙本身的弹性特征.裂隙参数的这个性质对于该理论在裂隙探测和裂隙含流体检测方面的进一步应用具有重要意义.通过数值模拟进一步说明,对于裂隙介质而言,EN和ET比Thomsen参数的物理意义更为明确和直观.     

基于辛格式奇异核褶积微分算子的地震标量波场模拟

本文在对地震波场进行模拟时,采用辛差分格式对波动方程进行时间离散,采用奇异核褶积微分算子对波动方程进行空间离散.该方法尽管增加了一些计算量,但提高了计算精度和稳定性;相对于其他非辛算法,它是全局保结构的,并且具有较强的长时间跟踪能力.该方法为解决大尺度、长时程地震波场的高精度模拟问题提供了一种新的、有效的选择.     

Accuracy of numerical simulations of contaminant transport in heterogeneous aquifers: A comparative study

This work deals with a comparison of different numerical schemes for the simulation of contaminant transport in heterogeneous porous media. The numerical methods under consideration are Galerkin finite element (GFE), finite volume (FV), and mixed hybrid finite element (MHFE). Concerning the GFE we use linear and quadratic finite elements with and without upwind stabilization. Besides the classical MHFE a new and an upwind scheme are tested. We consider higher order finite volume schemes as well as two time discretization methods: backward Euler (BE) and the second order backward differentiation formula BDF (2). It is well known that numerical (or artificial) diffusion may cause large errors. Moreover, when the Péclet number is large, a numerical code without some stabilising techniques produces oscillating solutions. Upwind schemes increase the stability but show more numerical diffusion. In this paper we quantify the numerical diffusion for the different discretization schemes and its dependency on the Péclet number. We consider an academic example and a realistic simulation of solute transport in heterogeneous aquifer. In the latter case, the stochastic estimates used as reference were obtained with global random walk (GRW) simulations, free of numerical diffusion. The results presented can be used by researchers to test their numerical schemes and stabilization techniques for simulation of contaminant transport in groundwater.     

Influence of spatial variations of microtopography and infiltration on surface runoff and field scale hydrological connectivity

Surface runoff on agricultural fields arises when rainfall exceeds infiltration. Excess water ponding in and flowing through local microtopography increases the hydrological connectivity of fields. In turn, an increased level of hydrological connectivity leads to a higher surface runoff flux at the field boundaries. We investigated the functional hydrological connectivity of synthetical elevation fields with varying statistical properties. For this purpose, we developed an object-oriented ponding and redistribution model to which Philip’s infiltration model was coupled. The connectivity behaviour is determined by the presence of depressions with a large area and spatial organization of microtopography in rills or channels. The presence of microdepressions suppresses the effect of the spatial variation of infiltration properties. Connectivity behaviour of a field with a varying spatial distribution of infiltration properties can be predicted by transforming the unique connectivity function that was defined for a designated microtopography.     

基于二次场的海洋可控源电磁法三维有限元正演

根据库伦规范势的定义,推导出关于磁矢量势和电标量势的偏微分方程,为了克服由电流源引起的奇异性和数值模拟计算困难,将电磁总场分解为一次场和二次场,一次场由基于Schelkunoff势函数的一维正演算法得到,二次场由有限元法计算得到,实现了海洋可控源电磁法三维有限元正演算法。通过一维数值模拟实例,验证该算法的计算精度。然后,利用该算法对带海底地形的三层储层模型进行正演,分析了海底地形对海洋控源电磁场各分量产生的影响。     

Hydraulic modeling of flood pulses in the Middle Bussento Karst System (MBSKS), UNESCO Cilento Global Geopark,southern Italy

Karst systems provide water for domestic and industrial uses and for generating hydropower, but they can also create fluvial hazards, such as upstream back‐flooding and downstream karst flash‐flood events. However, these hazards are difficult to foresee due to the complex recharge‐discharge processes as well as the lack of information on the inside of the system, which has often not been completely surveyed by speleologists or explored by boreholes. To overcome these difficulties, hydro‐chemical data from the monitoring system in the Middle Bussento Karst System (MBSKS), one of the first Experimental Karst Systems in southern Italy, were recorded and previously discussed. Based on shared background in flood karst hydraulic modeling, this paper describes the conceptual premises and rationale of a general‐purpose hydraulic model that is suitable both for the MBSKS and for other Mediterranean, multi‐recharge, mature, conduit‐dominated karst systems. To test the reliability of the model, simulations of time–space behavior and response are performed using natural and artificial flood pulses “as tracers”, considering a “pulse” as a significant variation in water quantity and/or quality. The results of the model explain the interactions between allogenic, autogenic, and anthropogenic recharges from differentiated sources and phreatic conduit systems. These results also clarify the overall response of karst springs at typical time scales of flood pulses. Table acronym name     

Using constrained inversion of gravity and magnetic field to produce a 3D litho‐prediction model

Geologically constrained inversion of gravity and magnetic field data of the Victoria property (located in Sudbury, Canada) was undertaken in order to update the present three‐dimensional geological model. The initial and reference model was constructed based on geological information from over 950 drillholes to constrain the inversion. In addition, downhole density and magnetic susceptibility measured in six holes were statistically analysed to derive lower and upper bounds on the physical properties attributed to the lithological units in the reference model. Constrained inversion of the ground gravity and the airborne magnetic data collected at the Victoria property were performed using GRAV3D and MAG3D, respectively. A neural network was trained to predict lithological units from the physical properties measured in six holes. Then, the trained network was applied on the three‐dimensional distribution of physical properties derived from the inversion models to produce a three‐dimensional litho‐prediction model. Some of the features evident in the lithological model are remnants of the constraints, where the data did not demand a significant change in the model from the initial constraining model (e.g., the thin pair of diabase dykes). However, some important changes away from the initial model are evident; for example, a larger body was predicted for quartz diorite, which may be related to the prospective offset dykes; a new zone was predicted as sulfide, which may represent potential mineralisation; and a geophysical subcategory of metabasalt was identified with high magnetic susceptibility and high density. The litho‐prediction model agrees with the geological expectation for the three‐dimensional structure at Victoria and is consistent with the geophysical data, which results in a more holistic understanding of the subsurface lithology.