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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Investigation of the groundwater system at Masaya Caldera,Nicaragua, using transient electromagnetics and numerical simulation
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Investigation of the groundwater system at Masaya Caldera,Nicaragua, using transient electromagnetics and numerical simulation

机译：使用瞬变电磁学和数值模拟研究尼加拉瓜马萨亚火山口的地下水系统

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The distribution of groundwater beneath Masaya Volcano, in Nicaragua, and its surrounding caldera was characterized using the transient electromagnetic method (TEM). Multiple soundings were conducted at 30 sites. Models of the TEM data consistently indicate a resistive layer that is underlain by one or more conductive layers. These two layers represent the unsaturated and saturated zones, respectively, with the boundary between them indicating the water-table elevation. A map of the TEM data shows that the water table in the caldera is a subdued replica of the topography, with higher elevations beneath the edifice in the south-central caldera and lower elevations in the eastern caldera, coinciding with the elevation of Laguna de Masaya. These TEM data, combined with regional hydrologic data, indicate that the caldera in hydrologically isolated from the surrounding region, with as much as 60 m of difference in elevation of the groundwater table across caldera-bounding faults. The water-table information and estimates of fluxes of water through the system were used to constrain a numerical simulation of groundwater flow. The simulation results indicate that basalt flows in the outer parts of the caldera have a relatively high transmissivity, whereas the central edifice has a substantially lower transmissivity. A layer of relatively high transmissivity must be present at depth within the edifice in order to deliver the observed flux of water and steam to the active vent. This hydrologic information about the caldera provides a baseline for assessing the response of this isolated groundwater system to future changes in magmatic activity.
机译：使用瞬变电磁法（TEM）表征了尼加拉瓜马萨亚火山下方的地下水分布及其周围的火山口。在30个地点进行了多次探测。 TEM数据模型始终显示出一层或多层导电层下面的电阻层。这两个层分别代表不饱和区和饱和区，它们之间的边界表示地下水位高程。 TEM数据图显示，破火山口中的地下水位是地形的柔和复制品，中南部破火山口的建筑物下方海拔较高，东部破火山口的海拔较低，与Laguna de Masaya的海拔高度一致。这些TEM数据与区域水文数据相结合，表明火山口与周围地区在水文上是隔离的，跨火山口的断层的地下水位高差高达60 m。地下水位信息和通过系统的水通量估算值被用来约束地下水流的数值模拟。仿真结果表明，在破火山口外部的玄武岩流具有较高的透射率，而中央建筑物的透射率明显较低。为了将观察到的水和蒸汽通量输送到主动通风口，必须在建筑物的深处存在一个相对较高的透射率层。有关破火山口的水文信息为评估该孤立的地下水系统对岩浆活动未来变化的响应提供了基线。

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