Rowberry Matt D, Martí Xavi, Frontera Carlos, Van De Wiel Marco J, Briestenský Miloš
Institute of Rock Structure & Mechanics, Czech Academy of Sciences, V Holešovičkách 41, 182 09, Prague 8, Czech Republic.
Institute of Physics, Czech Academy of Sciences, Cukrovarnická 10, 162 53, Prague 6, Czech Republic.
J Environ Radioact. 2016 Jun;157:16-26. doi: 10.1016/j.jenvrad.2016.02.023. Epub 2016 Mar 4.
Cave radon concentration measurements reflect the outcome of a perpetual competition which pitches flux against ventilation and radioactive decay. The mass balance equations used to model changes in radon concentration through time routinely treat flux as a constant. This mathematical simplification is acceptable as a first order approximation despite the fact that it sidesteps an intrinsic geological problem: the majority of radon entering a cavity is exhaled as a result of advection along crustal discontinuities whose motions are inhomogeneous in both time and space. In this paper the dynamic nature of flux is investigated and the results are used to predict cave radon concentration for successive iterations. The first part of our numerical modelling procedure focuses on calculating cave air flow velocity while the second part isolates flux in a mass balance equation to simulate real time dependence among the variables. It is then possible to use this information to deliver an expression for computing cave radon concentration for successive iterations. The dynamic variables in the numerical model are represented by the outer temperature, the inner temperature, and the radon concentration while the static variables are represented by the radioactive decay constant and a range of parameters related to geometry of the cavity. Input data were recorded at Driny Cave in the Little Carpathians Mountains of western Slovakia. Here the cave passages have developed along splays of the NE-SW striking Smolenice Fault and a series of transverse faults striking NW-SE. Independent experimental observations of fault slip are provided by three permanently installed mechanical extensometers. Our numerical modelling has revealed four important flux anomalies between January 2010 and August 2011. Each of these flux anomalies was preceded by conspicuous fault slip anomalies. The mathematical procedure outlined in this paper will help to improve our understanding of radon migration along crustal discontinuities and its subsequent exhalation into the atmosphere. Furthermore, as it is possible to supply the model with continuous data, future research will focus on establishing a series of underground monitoring sites with the aim of generating the first real time global radon flux maps.
洞穴氡浓度测量反映了一场持续竞争的结果，这场竞争使通量与通风及放射性衰变相互较量。用于模拟氡浓度随时间变化的质量平衡方程通常将通量视为常数。尽管这种数学简化回避了一个内在的地质问题，但作为一阶近似是可以接受的：进入洞穴的大部分氡是由于沿地壳不连续面的平流而呼出的，而这些不连续面的运动在时间和空间上都是不均匀的。本文研究了通量的动态性质，并将结果用于预测连续迭代的洞穴氡浓度。我们数值模拟过程的第一部分着重于计算洞穴气流速度，而第二部分则在质量平衡方程中分离出通量，以模拟变量之间的实时依赖性。然后就可以利用这些信息得出一个用于计算连续迭代的洞穴氡浓度的表达式。数值模型中的动态变量由外部温度、内部温度和氡浓度表示，而静态变量由放射性衰变常数和一系列与洞穴几何形状相关的参数表示。输入数据记录于斯洛伐克西部小喀尔巴阡山脉的德里尼洞穴。这里的洞穴通道沿着东北 - 西南走向的斯莫莱尼采断层的分支以及一系列西北 - 东南走向的横向断层发育。三个永久安装的机械引伸仪提供了断层滑动的独立实验观测数据。我们的数值模拟揭示了2010年1月至2011年8月期间的四个重要通量异常。这些通量异常中的每一个之前都有明显的断层滑动异常。本文概述的数学程序将有助于增进我们对氡沿地壳不连续面迁移及其随后向大气中呼出的理解。此外，由于可以为模型提供连续数据，未来的研究将集中于建立一系列地下监测站点，旨在生成首批实时全球氡通量图。
