Lerwick Observatory Monthly Magnetic Bulletin: August 2018

[摘要] ThevolcanicrocksoftheTroodosOphioliteComplexinCyprusrepresentapoor groundwatersource.Howeverinregionswheregroundwatersystemsaredevelopedalongfracturezones,waterboreholesarecapableofprovidingwaterforthelocal community,particularlyforagriculture.Inordertoincreasethesuccessrateofwater boreholes several geophysical methods weretrialed to investigate their ability to locate and charaterise fracture zones.Azimuthal apparent resistivity (AZR), very low frequencyelectromagnetics(VLF)and audio-magnetotellurics (AMT) were applied at a number of test sites on the Upper andLower Pillow Lava series and pillowlavas and dykes of the Basal Group. No distinct fracture zones were identified by the measurements. A conductive zone was identified over pillowlavas by AMT, but may have been due to a porous/more fractured layer or the conductive pillowlavas.TheAZRresultsclearlydemonstratetheheterogeneous nature of theTroodos volcanic rocks. Fracturing, where it has been identified, appears tobelocalisedandtobeoflimitedlateralextent.Azimuthal apparentresistivityis unlikelytobesuccessfulasaprimarygeophysicaltechniqueintheexplorationfor groundwater resources over theTroodos volcanic rocks. However it may be useful as a secondarytechnique,perhapsfortracingthestrikeofaknownfracturezonewhich gives high water yields. Due to the conductive nature of the pillowlavas theresistivity contrast offered by any near-surface fracture zones will inevitably be small and likely tobe below the detection limits of VLF.

[发布日期] 2000-01-01 [发布机构] British Geological Survey

[学科分类] 地球科学(综合)

[关键词] Geophysics;groundwater;Troodos Ophiolite;Cyprus