| Abstract |
The Allallobeda geothermal field is one of the three geothermal fields located in the Tendaho graben and the other two are Dubti and Ayrobera geothermal fields. The Tendaho graben is located in a topographic depression in the Afar region (NE Ethiopia), some 600 km from the capital city Addis Ababa. Radon soil geochemical study was conducted in the Allallobeda geothermal field in an area of 1.8 km from east to west by 2.2 km from south to north. The area was gridded one hundred by one hundred meters and the radon measurement was taken in Bq/m3 at every one hundred meters by digging one meter deep hole where the radon probe goes in. Temperature was recorded at 50 cm and 100 cm depth of the hole. Northing, Easting, Elevation, Date and Time were recorded at every point of the surveyed area. The aim of this study is to locate the Radon Soil gas measurement mainly applied to detect buried or hidden faults to understand the permeable zone and to pinpoint favorable structural locations for geothermal exploratory drilling aimed at tapping fluids from the deep-sited geothermal resource. As a result, total of 350 measurements were recorded. An SPSS statistical soft ware was applied to evaluate the basic characteristics of the data. Invariant statistical and graphical methods that are histogram and cumulative frequency diagrams were used to study each variable independently and give a visual representation of the data distribution able to highlight the presence of multiple populations. Even though the data display negatively skewed distribution, yet it is well approximated by log normal distribution known as normal curve or bell shaped curve. As a result 49.86% of the data represent the background, where as 25.4% represent the anomaly and 24.7% of the data represent the low values. The radon soil geochemical survey has enabled to reveal the distribution of buried faults, joints or fractures. The investigation confirms that the anomalous values are concentrated in the North-North-East / South-South-West (NNE/SSW) and North-South (NS) direction of the studied area. |