Geophysical exploration for groundwater resources over the volcanic rocks of the Troodos Ophiolite Complex, Cyprus

The volcanic rocks of the Troodos Ophiolite Complex in Cyprus represent a poor groundwater source. However in regions where groundwater systems are developed along fracture zones, water boreholes are capable of providing water for the local community, particularly for agriculture. In order to increase the success rate of water boreholes several geophysical methods were trialed to investigate their ability to locate and charaterise fracture zones. Azimuthal apparent resistivity (AZR), very low frequency electromagnetics (VLF) and audio-magnetotellurics (AMT) were applied at a number of test sites on the Upper and Lower Pillow Lava series and pillow lavas and dykes of the Basal Group. No distinct fracture zones were identified by the measurements. A conductive zone was identified over pillow lavas by AMT, but may have been due to a porous/more fractured layer or the conductive pillow lavas. The AZR results clearly demonstrate the heterogeneous nature of the Troodos volcanic rocks. Fracturing, where it has been identified, appears to be localised and to be of limited lateral extent. Azimuthal apparent resistivity is unlikely to be successful as a primary geophysical technique in the exploration for groundwater resources over the Troodos volcanic rocks. However it may be useful as a secondary technique, perhaps for tracing the strike of a known fracture zone which gives high water yields. Due to the conductive nature of the pillow lavas the resistivity contrast offered by any near-surface fracture zones will inevitably be small and likely to be below the detection limits of VLF.