etude petro structurale des chevauchements ductiles himalayens sur la transversale de l everest makalu nepal oriental tectonic and microtectonic data in eastern nepal indicate that the major observed thrusting 100 km on the main central thrust mct postdates the barrovian metamorphism of the high himalaya gneisses this result at variance with the famous reverse metamorphism model better explains the abnormal metamorphic superpositions in the himalayas and accounts for the lack of high pressure assemblages under the thick allochtonous high himalaya tibetan slab pressure and temperature estimates by microprobe analysis on plagioclase biotite garnet kyanite sillimanite and cordierite assemblages are presented for samples collected along the mct shear zone and across the gneiss slab in the everest makalu area since there is very little difference in pressure at the front of the slab kathmandu klippe and its root these estimates support the existence of important late metamorphic thrusting the decrease of pressure towards the top of the gneiss pile combined with a small temperature increase explains the k

polyphase metamorphism and the development of the main central thrust along a cross section through the lesser and higher himalayan units at the kishtwar window area north west india a polyphase barrovian type metamorphism has been delineated in relation to the development of the main central thrust mct in the metapelitic mineral assemblages three metamorphic phases have been distinguished a conditions up to amphibolite grade at moderate to high pressures alm rut ilm kya qtz characterize the m1 phase b pressure release and or temperature increase as a result of movement along the mct and the formation of gneiss domes in the higher himalaya as expressed by oriented n70 100 e fibrolite defines the m2 phase and c finally during uplift of the kishtwar window area a retrogressive m3 phase is characterized by the assemblage quartz muscovite chlorite both optically zoned and single stage garnets have been examined with the electron microprobe to determine their element partitioning normal zoning has been found in samples below the mct in the lesser himalaya indicating prograde growth during the m2 phase whereas tectonically above in the higher himalaya unit the garnets reveal double stage growth with a complex zoning pattern due to reaction partitioning during m1 and m2 and reverse zoning at their rims during the retrogressive m3 phase geothermometry on metapelites along a cross section through the mct zone and the higher himalaya imply distinct readjustments of garnet biotite exchange equilibria and indicate isothermal conditions 500 600 c throughout the section during the m3 retrogression pressure calculations gro an kya qtz and alm rut ilm kya qtz suggest a decrease in pressure towards the top of the section 6 7 5 to 4 5 5 kbar as corroborated by fibrolite replacing kyanite the spatially inverse metamorphism exposed within the lesser himalaya of the kishtwar window is regarded as a product of polyphase metamorphism combined with ongoing thrusting and shearing and is reflected by condensed m2 isograds around the kishtwar window

spatial delineation of groundwater salinity using deep time domain electromagnetic geophysical measurements a feasibility study 1 the objective of this study was to delineate the spatial distribution of fresh brackish and saline groundwater bodies as well as brine beneath the judea desert israel we used the deep time domain electromagnetic tdem geophysical system cycle 5m which provides the maximum exploration capability to depths 1 5 2 km below land surface the study was conducted at 21 locations at the desert plateau where fresh groundwater flows through the upper aquifers from the replenishment area at the judea mountains toward the dead sea springs in deeper aquifers brackish and saline groundwater bodies exist which originated from lakes and lagoons that existed at the dead sea rift valley during the pleistocene and pliocene respectively it was found that within carbonate formations fresh groundwater c 103 ppm total dissolved solids tds is characterized by a resistivity of more than 15 m brackish groundwater 103 c 104 ppm tds is characterized by 5 15 m saline groundwater 104 c 105 ppm tds is characterized by 0 5 5 m and brine 105 c ppm tds is characterized by less than 0 5 m

seasonal reversals in groundwater flow direction and its role in the recurrent agwagune landslide problem a geophysical and geological appraisal the character of the shallow subsurface materials in the landslide and flood prone agwagune community has been investigated using geophysical electrical resistivity geological and geotechnical techniques arising from the continuous suffering of the people in the affected areas high occurrence rate and the desire to characterise the surficial materials two dimensional resistivity tomography vertical electrical sounding soil sampling and hydrodynamic monitoring were conducted results show that the surficial materials are dominated by two main lithologic units thin sandy materials with resistivity 30 m and thick argillaceous materials with resistivity 30 m particle size analyses confirm the dominance of argillaceous silty clay 56 2 and very fine 55 3 over arenaceous 9 2 materials bulk and particle densities of the surficial materials vary from 0 99 103 to 1 40 103 and 2 06 103 to 2 50 103 kg m3 respectively ph ec and porosity range from 4 46 to 6 68 8 0 to 23 0 ms cm and 34 0 to 60 0 respectively atterberg limits vary from 15 82 to 38 70 for liquid limit and 18 10 24 00 for plastic limit plasticity index varies from 11 92 to 15 70 shallow groundwater in the coastal area is always in hydrodynamic equilibrium with water inside the cross and efefa rivers and pond fields to sustain this equilibrium condition excess water inside the cross river is usually discharged into efefa river through both surface and underground flow processes however when water inside the cross river dries up a new hydraulic gradient which distorts the existing equilibrium is formed this results in the reversal of groundwater flow direction continuous flow of groundwater into the cross river channel crc without any corresponding recharge results in the formation of voids which gravitational force forces to collapse the collapsed materials usually roll toward the crc resulting in landslides models illustrating the main cause of the repeated landslide problem and suggested measures to minimise its occurrence rate have been included

electrical methods ves and ert for identifying mapping and monitoring different saline domains in a coastal plain region alt emporda northern spain summary the spatial variability through time of the degree of salinity of soils and groundwater is a major issue concerning the sustainable management of water resources the problem is accentuated in coastal plain areas where saline bodies of different origin coexist we present an extensive geoelectrical resistivity dataset collected in the alt emporda clastic coastal aquifer system ne spain integrating the results of field campaigns undertaken within a period of more than two decades the dataset is unique in the literature and comprises highly valuable information for the investigation of saline domains the joint application of vertical electrical sounding ves and electrical resistivity tomography ert methods allowed the identification of saline domains and monitoring their evolution through time geophysical data gathered during field campaigns in 1982 2002 and 2010 were calibrated and interpreted on the basis of soil and groundwater physico chemical analyses and hydrogeological stratigraphic and geomorphological data the results illustrate the potential of electrical resistivity methods at differentiating saline domains in coastal aquifer areas and at modelling their configuration and evolution although the ves data processing allows solving the one dimensional resistivity structure of the subsurface the inversion imposes a 1d layered model thus interpretation of two dimensional structures is subject to the interpolation between discrete measures in contrast ert data offer a continuous 2d image of the resistivity distribution both laterally and in depth given that the bulk resistivity of the medium is extremely sensitive to salt content the ert profiles permitted identifying and determining the geometry of hyper saline areas characterized by resistivities of less than 5 m the study demonstrates the efficiency of the electrical methods to map subsurface conductive zones and illustrates how the accurate knowledge of the hydrogeological pattern results critical to meet this objective

using dc resistivity method to characterize the geometry and the salinity of the plioquaternary consolidated coastal aquifer of the mamora plain morocco the direct current resistivity method was applied to the consolidated coastal plioquaternary aquifer of mamora plain located on the atlantic coast of morocco the aim is to determine the depth of the base of the saturated zone in the aquifer and to help in imaging lateral and vertical distribution of groundwater salinity the geoelectric survey showed four geoelectric formations with the following electrical resistivities from top to bottom 20 80 200 2000 200 300 and 5 70 ohm m the latter designates the basement of the aquifer constituted of marls and sandy marls the mean resistivity of 250 ohm m designates the aquifer formation it decreases to less than 25 of its initial values for the soundings near the shore reflecting the oceanic impact on the aquifer formation resistivity the contour map shows that the basement of the saturated zone in the aquifer is deeper in the northwest near the sebou river estuary with values up to 70 m below sea level this results in a larger thickness of the saturated zone of the aquifer leading to a consequent hydraulic potential on the other hand it has been deduced that the extent of marine intrusion inside the continent can be governed by human activities natural properties and substratum geometry of the aquifer as well as by ecological factors an optimal network of electrical soundings has been proposed for the monitoring of saltwater intrusion

evolution of saline waters and brines in the benue trough nigeria abstract hydrogeochemical assessment of 40 saline waters and brines from 20 locations within the lower southern and middle regions of the benue trough nigeria are presented and discussed in terms of genesis of the primary salinity and subsequent hydrochemical evolution the total dissolved ions range from 5263 to 88 800 mg l and 5148 to 47 145 mg l in the lower and middle region respectively the saline waters and brines are characteristically na cl type enriched in ca and sr on the one hand and depleted in mg and so 4 on the other relative to the seawater evaporation trend ionic ratios na cl br systematic and divalent cations suggest two likely sources of primary salinity a fossil seawater source and dissolution of halite however water rock interaction involving mg uptake by clay minerals and possibly dolomitization during diagenesis appear to be responsible for further modification of the primary chemistry a conceptualized hydrogeological flow model for the brines is presented

salinity mapping of coastal groundwater aquifers using hydrogeochemical and geophysical methods a case study from north kelantan malaysia integrated hydrogeochemical and geophysical methods were used to study the salinity of groundwater aquifers along the coastal area of north kelantan for the hydrogeochemical investigation analysis of major ion contents of the groundwater was conducted and other chemical parameters such as ph and total dissolved solids were also determined for the geophysical study both geoelectrical resistivity soundings and reflection seismic surveys were conducted to determine the characteristics of the subsurface and groundwater contained within the aquifers the ph values range from 6 2 to 6 8 indicating that the groundwater in the study area is slightly acidic low content of chloride suggests that the groundwater in the first aquifer is fresh with an average concentration of about 15 8 mg l and high geoelectrical resistivity 45 ohm m on the other hand the groundwater in the second aquifer is brackish with chloride concentration ranging from 500 mg l to 3 600 mg l and very low geoelectrical resistivity 1 000 mg l the groundwater in the third aquifer is fresh with chloride concentrations generally ranging from 2 mg l to 210 mg l and geoelectrical resistivity of greater than 45 ohm m fresh and saltwater interface in the first aquifer is generally located directly in the area of the coast but for the second aquifer both hydrogeochemical and geoelectrical resistivity results indicate that the fresh water and saltwater interface is located as far as 6 km from the beach the considerable chloride ion content initially suggests that the salinity of the groundwater in the second aquifer is probably caused by the intrusion of seawater however continuous monitoring of the chloride content of the second aquifer indicated no significant changes with time from which it can be inferred that the salinity of the groundwater is not affected by seasonal seawater intrusion schoeller diagrams illustrate that sulphate concentrations of the groundwater of the second aquifer are relatively low compared to those of the recent seawater therefore this result suggests that the brackish water in the second aquifer is probably from ancient seawater that was trapped within the sediments for a long period of time rather than due to direct seawater intrusion

groundwater investigation in kuala selangor using vertical electrical sounding ves surveys integrated geoelectrical and hydrochemical surveys were used to investigate and delineate different types of groundwater in the kuala selangor alluvial aquifer previous hydrogeological borehole investigation showed that this aquifer contains several types of groundwater in relation to its salinity the high salinity of the groundwater in some areas is believed to be due to either saltwater intrusion from the nearby sea or river infiltration during high tide season the vertical electrical sounding ves method was employed to study and map the subsurface variation of resistivity in the area for each sounding measurement a total spread length of 300 m was obtained with a vertical depth penetration of about 60 to 75 m chemical analysis of the groundwater samples taken from both shallow and deep boreholes was carried out for the water quality determination a total of 45 ves stations were succesfully established along three parallel roads with a direction almost perpendicular to the coastal line the distance between stations varies from 1 to 2 km with a maximum length of about 60 km surveyed line results of the vertical electrical soundings as well as the hydrochemistry of the groundwater samples show that the soil and groundwater in the study area can be grouped into fresh and brackish water zones the subsurface resisitivity sections derived from the ves study suggest that the area is dominated by brackish soil and groundwater zones especially in the area towards the coast this result appears to agree well with the groundwater pumped from boreholes scattered around in the area water drawn from boreholes near the coast showed higher salinity compared to the water pumped from inland boreholes chloride values greater than 250 mg l are considered to represent the brackish zones whilst values less than 250 mg l represents zones of fresh soil and groundwater

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

gold predictivity mapping in french guiana using an expert guided data driven approach based on a regional scale gis the realistic estimation of gold mining in french guiana requires including the numerous illegal gold washing activities in predictivity mapping the combination of a classical approach based on the algebraic method of knox robinson and groves with innovative processing grid type geochemical and radiometric data as well as cluster analysis technique provides a better understanding of the structure of studied mineralized areas

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

benue trough and benue chain it is suggested that the benue trough may have been initiated by the extension of the equatorial oceanic fracture zones onto the continent during the early stages of the separation of africa and south america a transcurrent movement along deep seated faults of the basement is responsible for the structure of the trough after a period of extension characterized by the sedimentary infilling of the trough and igneous activity the trough is turned into a chain through a short phase of compression a discrete pattern of en echelon folds and the strain pattern deduced from the analysis of large scale and microfracturing correspond to a n s to n160 e direction of compression coupled to a sinistral transcurrent movement along a ne sw direction the difference in age of the folding phase in the northern and southern parts of the chain indicates a diachronous nature for this tectonic event in relation to the wrench regime the tertiary evolution of the trough marked by a tensional regime resulting in an e w extension is to be related to the cameroon volcanic line

the use of vertical electrical sounding resistivity method for the location of low salinity groundwater for irrigation in chaj and rachna doabs a geoelectrical resistivity survey using vertical electrical sounding ves was conducted at chaj doab land between rivers jhelum and chenab pakistan and rachna doab land between rivers chenab and ravi pakistan with the objective of investigating groundwater conditions a total of 90 sites were selected with 43 sites in chaj and 47 sites in rachna doabs the resistivity meter abem terrameter sas 4000 sweden was used to collect the ves data by employing a schlumberger electrode configuration with half current electrode spacings ab 2 ranging from 2 to 180 m and the potential electrode mn from 1 to 40 m the field data were interpreted using the interpex ix1d computer software and the resistivity versus depth models for each location was estimated the outputs of subsurface layers with resistivities and thickness presented in contour maps and 3 d views by using surfer software were created a total of 102 groundwater samples from nearby hydrowells at different depths were collected to develop a correlation between the aquifer resistivity of ves and the electrical conductivity ec of the groundwater and to confirm the resulted geophysical resistivity models from the correlation developed it was observed that the groundwater salinity in the aquifer may be considered low and so safe for irrigation if resistivity 45 m and marginally fit for irrigation having resistivity between 25 and 45 m the study area has resistivities from 3 9 to 2 222 m at the top of the unsaturated layer between 1 21 and 171 m in the shallow aquifers and 0 14 152 m in the deep aquifers of the study area the results indicate that the quality of groundwater is better near the rivers and in the shallow layers compared to the deep layers

assessment of the state of soils shallow sediments and groundwater salinity in abi cross river state nigeria abi area in nigeria borders the salinity enriched lower benue trough lbt and plans are currently underway to extend large scale irrigation facilities under construction in the lbt to abi area in order to generate baseline soil and water salinity information about abi area under non irrigation condition integrated information from constrained analyses of vertical electrical sounding data two dimensional electrical resistivity tomographies and laboratory analyses of soil and water samples were used to assess and map the spatial salinity distribution existence of widespread heterogeneities in the distribution of soil and water salinity between the shaly and sandy materials that dominate the shallow geology of the area was observed minimum values of water electrical conductivity wec and total dissolved solids tds were observed to be 19 2 s cm and 13 mg l respectively in the sandstone dominated areas maximum values of wec and tds were observed to be 931 0 s cm and 624 mg l respectively within the shale dominated areas soil electrical conductivity was observed to vary from 5 0 s cm in the sandstone areas to 14 0 s cm in the shale dominated areas minimum and maximum soil ph observations were 4 53 in the shale dominated area and 6 55 in the sandstone dominated area respectively these results show that the water and soil resources in the area vary from fresh to slightly saline and non saline to high salinity levels respectively consequently both resources are still good for agricultural purposes

electrical resistivity and seismic refraction tomography to detect buried cavities near surface cavities can pose serious hazards to human safety especially in highly urbanized town centres the location of subsurface voids the estimation of their size and the evaluation of the overburden thickness are necessary to assess the risk of collapse in this study electrical resistivity tomography ert and seismic refraction tomography data are integrated in a joint interpretation process for cavity location in the city of rome ert is a well established and widely employed method for cavity detection however additional information provided by seismic refraction tomography is capable of eliminating some potential pitfalls in resistivity data interpretation we propose that the structure of the cavities defined by ert can be used as a base to optimize seismic refraction tomography investigations within the framework of a joint interpretation process data integration and the insertion of a priori information are key issues for reducing the uncertainties associated with the inversion process and for optimizing both acquisition procedures and computation time herein the two geophysical methods are tested on both synthetic and real data and the integration of the results is found to be successful in detecting isolated cavities and in assessing their geometrical characteristics the cavity location inferred by geophysical non invasive methods has been subsequently confirmed by direct inspection

assessment of the reliability of 2d inversion of apparent resistivity data the reliability of inversion of apparent resistivity pseudosection data to determine accurately the true resistivity distribution over 2d structures has been investigated using a common inversion scheme based on a smoothness constrained non linear least squares optimization for the wenner array this involved calculation of synthetic apparent resistivity pseudosection data which were then inverted and the model estimated from the inversion was compared with the original 2d model the models examined include i horizontal layering ii a vertical fault iii a low resistivity fill within a high resistivity basement and iv an upfaulted basement block beneath a conductive overburden over vertical structures the resistivity models obtained from inversion are usually much sharper than the measured data however the inverted resistivities can be smaller than the lowest or greater than the highest true model resistivity the substantial reduction generally recorded in the data misfit during the least squares inversion of 2d apparent resistivity data is not always accompanied by any noticeable reduction in the model misfit conversely the model misfit may for all practical purposes remain invariant for successive iterations it can also increase with the iteration number especially where the resistivity contrast at the bedrock interface exceeds a factor of about 10 in such instances the optimum model estimated from inversion is attained at a very low iteration number the largest model misfit is encountered in the zone adjacent to a contact where there is a large change in the resistivity contrast it is concluded that smooth inversion can provide only an approximate guide to the true geometry and true formation resistivity

delineation of saltwater intrusion into the freshwater aquifer of lekki peninsula lagos nigeria recently the deterioration of water quality in the coastal zones of lekki peninsula area of lagos due to saltwater infiltration into the freshwater aquifer has become a major concern with the aim of providing valuable information on the hydrogeologic system of the aquifers the subsurface lithology and delineating the groundwater salinity vertical electrical resistivity ves sounding survey was carried out utilizing surface schlumberger electrode arrays and electrode spacing varying between 1 and 150m the dc resistivity surveys revealed significant variations in subsurface resistivity also the ves resistivity curves showed a dominant trend of decreasing resistivity with depth thus increasing salinity in general the presence of four distinct resistivity zones were delineated viz the unconsolidated dry sand a having resistivity values ranging between 125 and 1 028 m represent the first layer the fresh water saturated soil zone b having resistivity values which correspond to 32 256 m is the second layer the third layer zone c is interpreted as the mixing transition zone of fresh with brackish groundwater the resistivity of this layer ranges from 4 to 32 m while layer four zone d is characterized with resistivities values generally below 4 m reflecting an aquifer possibly containing brine the rock matrix salinity and water saturation are the major factors controlling the resistivity of the formation moreover this investigation shows that saline water intrusion into the aquifers can be accurately mapped using surface dc resistivity method

origin of the inverted metamorphism of the lower himalayas central nepal abstract the southern slope of the central nepal himalayas is divided geologically by the main central thrust zone into the underlying midland metasediment zone lower himalayas in the south and the overlying himalayan gneiss zone higher himalayas in the north the former zone consists of a thick pile of various kinds of metasediments folded into an anticlinorium and the latter zone consists of high grade crystalline rocks with a north dipping homoclinal structure and is further overlain by the tethys himalayas composed of non or slightly metamorphosed tethyan sediments the main central thrust zone shows a characteristic lithology such as calcareous schist quartzite phyllitic schist and augen gneiss and is intensely mylonitized the mineral composition and paragenesis of the rocks in the present area indicate an inverted metamorphism from the midland metasediment to the main central thrust zones that is the metamorphic grade of the midland metasediment zone increases upward toward the thrust zone from the chlorite to the biotite zones of the greenschist facies and the greenschist amphibolite transitional zone is attained in the thrust zone the himalayan gneiss zone is apparently much higher in metamorphic grade than the thrust zone on the basis of the compositional zoning of garnets and muscovite compositions however it is concluded that the himalayan gneisses suffered a polymetamorphism the younger metamorphism resulted in a retrograde metamorphism of the himalayan gneisses together with the above mentioned inverted metamorphism and an anatectic melting in depth this was caused by shear heating due to the thrust movement along the main central thrust zone during the alpine tectonism the older metamorphism which seems to be precambrian in age was much higher in metamorphic grade than the younger one and formed the pyrope rich cores of garnets in the himalayan gneisses the maximum metamorphic temperature of 550 c estimated from the mineral paragenesis in the thrust zone is compatible with that caused by shear heating due to the thrusting with thrusting velocity of 5 10 cm yr maximum stress of 300 bars and thrusting distance of 250 km bird 1978

integrated geophysical geochemical and hydrogeological investigation of shallow groundwater resources in parts of the ikom mamfe embayment and the adjoining areas in cross river state nigeria information generated from geophysical geochemical and hydrogeological data has been used in assessing the groundwater resource potential quality and usability and in mapping flow directions within the shallow subsurface of the mamfe embayment cross river state nigeria the electrical resistivity technique in which the schlumberger s vertical electrical sounding field procedure has been adopted was the geophysical method employed lithology logs from drilling records discharge rates static water level information were the hydrogeological information utilized while the geochemical techniques involve analyses of water samples apparent resistances were measured using different resistivity meters including oyo mcohm model 2115 abem terrameter sas300b and sas1000 models and igis ssp ats mrp model with maximum current electrode separation reaching 1 km in some communities geological information was used as control in the modelling and interpretation of all geophysical data the physico chemical parameters of the water samples from the different water sources in the area were determined using different analytical techniques and in some cases by in situ direct measurement of some parameters measured values of electrical conductivity static water level available aquifer discharge information and calculated sar and na were integrated into the geophysical and hydrogeological results the shallow subsurface of the area is segmented into four hydrogeological provinces crystalline basement province cbp cross river plain province crpp nkporo afikpo shales province nasp and alluvial buried river province abrp with localized groundwater flow patterns results indicated that the alluvial discharge rate of 3 83 l s fractured sandstone discharge rate of 2 43 l s and basement discharge rate of 1 80 l s aquifers are more yielding than the aquifers in areas covered with deformed shales discharge rate of 0 62 l s and siltstone aquifers discharge rate of 0 97 l s the aquifer horizons are inhomogeneous and anisotropic with topography and lithology exerting significant influence on groundwater flow direction however there appears to be some high yielding aquifers at depths greater than 100 m in the crpp areas although researches on their distribution are still ongoing precipitation is the major source of recharge and the water is enriched with na k ca2 mg2 text hco 3 cl text so 4 2 and text no 3 throughout the year graphical analyses of hydrochemical data using piper and stiff diagrams show that ca mg co3 hco3 is the dominant water facies results from ec sar and na show that the water is fresh and belongs to the good to excellent class and is therefore suitable for domestic agricultural and industrial use

a new tectonic model for the cameroon line central africa abstract the cameroon line a major geological feature in central africa has been considered successively as a series of horsts and grabens a continental rift and a mega shear zone it is marked out by about 60 anorogenic complexes and a dozen volcanic centres all of which have alkaline affinity remote sensing allows us recognition of the main lineament trends n70 n s n135 and e w while autocorrelation analysis reveals a major fault zone striking n30 in western cameroon and n15 in the northern region a mega left lateral shear zone is the model that best accounts for the fracture pattern and associated features such as linear and circular structures alignment of subvolcanic complexes syntectonic leucogranites marking out older shear zones and vein dykes the n70 adamawa fault zone a pan african fracture reworked during albian aptian times is the only shear zone of continental scale that could have initiated en echelon mega tension gashes within the cameroon line during a cainozoic left lateral transcurrent movement

three dimensional geophysical anatomy of an active landslide in lias group mudrocks cleveland basin uk a geoelectrical investigation of a slow moving earth slide earth flow in lower jurassic lias group rocks of the cleveland basin uk is described these mudrock slopes are particularly prone to failure and are a major source of lowland landslides in the uk but few attempts have been made to spatially or volumetrically characterise the subsurface form of these slides the primary aim of this study was to consider the efficacy of fully three dimensional geoelectrical imaging for landslide investigation with reference to a geological setting typical of lias group escarpments the approach described here included a reconnaissance survey phase using two dimensional electrical resistivity tomography ert resistivity mapping self potential sp profiling and mapping followed by a detailed investigation of an area of the landslide using three dimensional 3d ert and self potential tomography spt interpretation of the geophysical data sets was supported by surface observations aerial lidar and differential gps geomorphological surveys and intrusive investigations boreholes and auger holes the initial phase of the study revealed the existence of a strong sp signature at the site consistent with a streaming potential source and established the relationships between the main geological units the geomorphologic expression of the landslide and the resistivity of the materials in and around the study area the 3d spt model generated during the second phase of the study indicated drainage patterns across the landslide and preferential flow from the low permeability mud rocks into the underlying more permeable sandstone formation because of favourable resistivity contrasts between the clay rich whitby mudstone formation landslide material and the underlying staithes sandstone formation the volumetric 3d ert image allowed a number of surface and subsurface landslide features to be identified and spatially located these included the lateral extent of slipped material and zones of depletion and accumulation the surface of separation and the thickness of individual earth flow lobes and the dipping in situ geological boundary between the whitby mudstone and staithes sandstone bedrock formations