Resistivity Survey in the Alid Geothermal Area, Eritrea, a Joint Interpretation of TEM and MT Data

Abstract

A geophysical survey of the Mt. Alid geothermal area in Eritrea was performed in late 2008. The aim of the survey was to delineate the geothermal reservoir by the use of Transient Electro Magnetism (TEM) and Magnetotelluric (MT) resistivity soundings. The original plan was to cover the area of Mt. Alid and its nearest vicinity. The terrain, however, was very difficult for vehicles and bikes used for transportation of the equipment and inaccessible at times. The area to the west and southwest of the mountain was covered as well as the top of Mt. Alid, within the allotted timeframe. A total of 67 TEM and 52 MT soundings were performed in 24 days. The TEM and MT soundings were performed in the same place. The TEM revealed the shallow resistivity structure and MT the deeper part. The TEM data were also used for static shift correction in the MT data through a joined 1-D inversion of the two data sets.
A SW-NE lineament is detected at a depth interval of 500 metres to 2 km, and interpreted as a transform fault intersecting the geothermal reservoir which most likely controls the main upflow from the reservoir.
The surface on the southwest flanks of Mt. Alid has an area with exceptional vegetation in comparison to the barren dry volcanic landscape around. This indicates moisture and water in the ground that could be explained by steam flowing up from the geothermal reservoir.