Application Of Integreated Geophysical Methods For The Evaluation Of Thermal Centers And Their Structural Controls In Bokunazareth Main Ethiopian Rift

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In this work combined Vet1ical Electrical Sounding (VES), Dipole-Dipole profiling andrnmagnetic surveys are carried out around the Boku thermal area near Nazareth town, The analysisrnof the results obtained from the integrated geophysical methods has provided useful infOlmationrnregarding the electrical characteristics of the subsurface, which is related to the thickness andrndepth ranges of the different subsurface layers. The physical propelty distribution, which isrnobtained by these surveys, is analysed with pal1icular significance for thermal water andrnstructural controls.rnNine Vel1ical Electrical Sounding (VES) measurements using the Schulumberger configurationrnalong two pm'aBel profiles were calTied out. The field apparent resistivity data is plotted againstrnelectrode separation and initial model parameters for each sounding station are obtained usingrntwo layer master curves and the auxilimy point charts. For quantitative evaluation of thernresistivity soundings, the field data were fed to an iterative computer program, In this programrnthe apparent resistivities obtained as a function of electrode spacings are converted to truernresistivities as a function of depth, Using the initial model parameters obtained from curvernmatching, the computer program iteratively modifies the resistivities to obtain the best fit with thernfield data for the layer thickness chosen for the model.rnBased on the inversion, a five-layered geoelectric section is obtained along the first profilernexcept at YES 2, which has got a three-layer em1h stmcture. A unique distribution of subsurfacernresistivity has been obselved at YES 4 and on the second profile. This unique subsurfacernresistivity is charactelised by a velY low resistivity value for the large electrode separation. Thisrnbehaviour may actually be associated with the high conductance of the deep layers. The locationrnof the Baku thelmal centre, which is between the position of YES 5 and 6, has a four and fivernlayered earth stmcture. From the geoelectric section it is expected that a fault zone may be thestructural contact zone, A pattem of velY l~w resis:tivity: V~IJe' IS' observ'ed at' th~ position' ofrnYES2, which is bounded by a velY high resistivity value at the position ofVES 1 and YES 3. Arnlithological contact zone may be expected around the location of YES 1 and YES 2. The samernresistivity difference is observed between YES 5 and YES 6. YES 4 has shown a typical nature,rnwhich is characterised, by a velY low resistive zone. To ensure the real elech'ical behaviour of thernarea an additional geophysical method such as gravity methods may be more valuable.rnThe second profile consists of YES 7,8 and 9 and YES 7 has a seven layered earthrnsh'ucture, YES 8 has a tlu'ee layered ealth structure and YES 9 had a four layered eatth structure.rnAlong profile 2 the interesting behaviour is the velY low resistive zones for the large electrodernseparation which indicates the deep structural and geological features of the study area.rnThe dipole- dipole profiling psedosection section has been carded out only along the firstrnprofile. Here also, very low resistive zone is investigated around the location of the first segment,rnwhich is the position of YES 1, 2 and 3. Also velY low resistive zone is investigated around YESrn5 and·6 that is the Boku thelmal centre. Segment two of the profiling pseudosection generallyrnindicates a high resistive zone.rnThe magnetics survey shows generally qualitative information. A velY low magnetic responsernis observed around the location of YES 1 for the first profile. Along the second profile a velY lowrnmagnetic response is observed around the location of YES 2 and YES 5, which might bern'.' associated with the fault or fracture in the area. Again profile 3 has shown a velY low magneticrnresponse around the position ofVES.

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Application Of Integreated Geophysical Methods For The Evaluation Of Thermal Centers And Their Structural Controls In Bokunazareth Main Ethiopian Rift

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