The role of soil gas radon survey in exploring unknown subsurface faults at Afamia B dam, Syria

摘要

The purpose of this work is to determine a possible connection between anomalous radon values and some expected subsurface geological faults at Afamia B dam which is currently suffering a serious problem of large leakage through its bedrocks. A total of 82 soil gas radon sampling points were measured, using direct active method, over an area of 300 x 300 m which almost covers the entire surface of the reservoir basin. The results revealed a reasonable correlation between the geometric pattern of radon anomalies and the probable orientation of some underlying tectonic lineaments. Abnormal radon values, with peak signals of about 2-5 times higher than the background level, led to the detection of two probable fractured zones, denoted as F-1 and F-2. The data analysis suggests that the leakage of water from Afamia B dam almost runs vertically downwards along N60E trending fault zone F-2. Such a fault is very likely extending down within the Neogene formation to reach the permeable karstic carbonate rocks of Cretaceous at depth, forming large conduits through which the water of the reservoir is possibly drained off. This suggestion was in agreement with the general direction of the groundwater flow in the study area which indicates clearly that the supposed fractured zone F-2 may represent a catchment area for groundwater, and thereby it may constitute the most important structural element concerning the leakage problem of Afamia B reservoir.