, N. SURIYAARACHCHI

A magnetotelluric survey was conducted to map the lateral variation of resistivity with depth along ~9 km profiles across seven known hot springs of Sri Lanka for locating thermal waters within deep faults or hot dry rock that would help geothermal energy development. Data show three regions with resistivity less than 10 Ωm, two the vicinity of Kinniya hot spring, at depths ~1.5 and 2 km, and one at Kapurella at ~500 m. All three regions have 2D cross sections of a few hundred square metres. Three more regions with lower resistivity, 10- 100 Ωm, were located at depths beyond 10 km at Padiyatalawa, Mahaoya and Kinniya. Their cross sectional extent is limited to a few square kilometres. It is known that optimum geothermal sources at the spring sites can be lateral to the MT traverses, and that 3D MT surveys should be undertaken to locate the most favourable geothermal reservoirs. Though the larger detected sources are outside the economic depth of exploitation, results show their association with hot springs, which means under favourable connectivity and/or with induced hydro-fracturing, extraction of thermal water could be achieved at shallower depths