crosshole ip imaging for engineering and environmental applications induced polarization ip imaging is a promising tool in engineering and environmental studies application of this technique for near surface investigations has previously been limited by incomplete understanding of the physicochemical controls on the ip response together with a lack of appropriate methods for data inversion as laboratory studies have shown description of ip in terms of complex electrical conductivity enables access to various structural characteristics pertinent to practical issues such as subsurface lithology definition hydraulic permeability estimation or hydrocarbon contaminant mapping in particular analysis in terms of real and imaginary conductivity components offers improved lithological characterization since surface polarization effects are separated from electrolytic and surface conduction effects an occam type ip inversion algorithm based on complex algebra is described which accounts for these advances in ip interpretation by directly solving for complex conductivity results from crosshole applications at two case study sites demonstrate the suitability of the ip imaging approach for subsurface characterization in the first case study the imaging results correlate with the observed complex sequence of quaternary sediments at a waste disposal site characterization of the polarizability of these sediments offers significant value in lithological differentiation in the second case study the results of ip imaging at a hydrocarbon contaminated site illustrate the potential of the method in environmental studies the hydrocarbon location is clearly evident from the ip image and a markedly different response is observed at an uncontaminated region of the site by adopting empirical structural electrical relationships images of textural and hydraulic properties are estimated as a step toward improved quantitative characterization the success of the method for these contrasting applications supports further investigation into understanding the physical and chemical processes that control observed ip

assessment of groundwater contamination around active dumpsite in ibadan southwestern nigeria using integrated electrical resistivity and hydrochemical methods investigation of groundwater contamination due to leachate migration in a solid waste disposal site was done using both geophysical and hydrochemical methods the main goals were to delineate groundwater contamination due to leachate percolation and thus assessment of quality of groundwater from nearby hand dug wells bordering the dumpsite for drinking purpose a total of ten resistivity traverses were acquired within and outside the dumpsite using wenner configuration with constant electrode separation ranging from 5 to 25 m the 2d resistivity data were processed and inverted using res2dinv and res3dinv softwares respectively geochemical assessment of groundwater samples were carried out according to apha standards while hydrochemical facies of the sampled groundwater was evaluated using piper trilinear software the inverse resistivity models of the subsurface from 2d and 3d imaging revealed low resistivity value less than 10 m suspected to be leachate while 3d inverse sections allowed delineation of leachate weathered layer bedrock and seepage path from the dumpsite the extent of migration was more pronounced in the southern part of the dumpsite hence possible contamination of shallow groundwater system as dumpsite ages the results of physico chemical analyses showed the groundwater samples to be within the limits of who nsdwq for drinking purpose however higher values of concentrations of most analyzed parameters were noticed in well 1 due to its nearness to dumpsite and well 10 due to agricultural activities respectively interpretation of piper diagram showed cahco3 to be dominant facie in the area while alkaline earth metals text ca 2 text mg 2 and weak acids hco3 co3 are dominant cations and anions during both climatic seasons groundwater in the study area is of hard fresh and alkaline in nature

pacific north america plate boundary reorganization in response to a change in relative plate motion offshore canada 1 the transition from subduction in cascadia to the transform queen charlotte fault along western canada is often drawn as a subduction zone yet recent studies of gps and earthquake data from northern vancouver island are not consistent with that model in this paper we synthesize seismic reflection and gravity interpretations with microseismicity data in order to test models of 1 microplate subduction and 2 reorganization of the preexisting strike slip plate boundary we focus on the critical region of outer queen charlotte sound and the adjacent offshore on much of the continental shelf several million years of subsidence above thin crust are a counterindicator for subduction an undated episode of compression uplifted the southernmost shelf but subsidence patterns offshore show that recent subduction is unlikely to be responsible previously unremarked near vertical faults and a mix of extensional and compressional faults offshore indicate that strike slip faulting has been a significant mode of deformation seismicity in the last 18 years is dominantly strike slip and shows large amounts of moment release on the revere dellwood fault and its overlap with the queen charlotte fault the relative plate motion between the pacific and north american plates rotated clockwise 6 ma and appears to have triggered formation of an evolving array of structures we suggest that the paleo queen charlotte fault which had defined this continental margin retreated northward as offshore distributed shear and the newly formed revere dellwood fault propagated to the northwest

the winona basin structure and tectonics a compilation of published and new geophysical data from the winona basin off northern vancouver island has allowed a detailed interpretation of the sedimentary and tectonic history of the region to be made the basin is forming as a result of the asymmetric subsidence of a recently isolated lithospheric block that is slowly converging with the continental margin the crust beneath the basin is young 1 5 ma increasing in age from southeast to northwest and of normal oceanic thickness it is virtually non magnetic however probably because of its having been rapidly buried by turbidite sedimentation subsidence of the basin and uplift of the paul revere ridge began in the early pleistocene ca 1 8 ma and since that time up to 8 km of turbidite sediments has accumulated in the basin the nature of the fanning of the deposits suggests that the basin has been kept full throughout its history the minimum average supply rate necessary to accomplish this is about 70 106 mg year 1 this pleistocene ave

induced polarization detection and mapping of contaminant plumes several laboratory and scaled model investigations suggest that organic contaminants affect the surface electrical properties of exposed soils rocks and therefore produce measurable induced polarization ip signatures however there is little field evidence of an ip methodology for contaminant mapping a2d time domain ip method is developed for mapping the fs12 contaminant plume at the massachusetts military reservation mmr located in cape cod massachusetts the fs 12 plume consists of approximately 265 m 3 of fuel that erupted from a broken underground pipeline in the early 1970s benzene and ethylene dibromide edb are the primary contaminants at fs 12 with concentrations exceeding the allowed maximum concentration levels mcl while other constituents of the plume did not exceed their mcl therefore the contaminants of interest are benzene and edb partly because of their health risk and partly because they present the highest concentrations 2400 and 1000 g l respectively among the plume constituents and are therefore more likely to be related to the polarization source ip data were acquired along a survey line that partially transects the plume extending over contaminated and uncontaminated zones and were inverted to give 2d resistivity and chargeability plots to 100 m depth and a horizontal extent of 400 m by separately inverting ip data derived from time windows located at short and long decay times a timedomain gross spectral chargeability difference is produced both the chargeability and gross spectral chargeability difference show good agreement with the known location of the plume from monitoring wells with the ip chargeability section suggesting contaminant distribution detail that cannot otherwise be inferred from the sparse borehole distribution

continental signature of a ridge trench triple junction northern vancouver island south of the juan de fuca pacific north america triple junction located off northern vancouver island there is subduction and to the north there is oblique convergence along the queen charlotte transform fault in the mid tertiary periods of extension including crustal thinning and volcanism formed queen charlotte basin heat flow on northern vancouver island 67 mw m2 is the same as in queen charlotte basin to the north but it decreases abruptly to the south over a distance of 70 km to an average value of 46 mw m2 compared to the rest of the island the northern island has more subdued topography a lower mean elevation slightly higher bouguer gravity values and lower seismicity late tertiary volcanics which occur only on the northern part of the island geochemically resemble the tertiary masset formation which formed during periods of extension in queen charlotte basin these data are consistent with a tertiary history including periods of extension for northern vancouver island similar to queen charlotte basin and distinguish it from the rest of vancouver island the southern boundary of this northern block extends northeastward from brooks peninsula approximately above the inferred northern edge of the subducted juan de fuca plate and parallel to a series of linear magnetic anomalies associated with a northeasterly trending fault zone the abrupt transition in observed heat flow is most likely associated with the edge of the subducted plate which produces large temperature differences at depths of 30 40 km the time constant for these thermal effects to reach the surface conductively indicates that this boundary has been stable over tens of millions of years and therefore the location of the subducting plate s northern edge must have been stationary or moving very slowly over this period consequently it is likely that the triple junction has been located on average for the last 40 myr off brooks peninsula

resistivity and induced polarization monitoring of salt transport under natural hydraulic gradients we demonstrate the use of resistivity induced polarization ip monitoring of salt transport under natural hydraulic loads electrical monitoring of saline tracer transport during forced injection has been demonstrated previously detection of tracer transport under natural hydraulic loading is difficult because neither the hydraulic load nor the tracer resistivity can be controlled in one study we identify the electrical response to salt transport in a dynamic beach environment resistivity ip imaging resolved the structure of the saltwater freshwater interface and evidence for tide induced groundwater transport resistivity increases in the near surface and at depth upbeach of the high tide mark accompanied by tidal transgression we attribute this to desaturation and decreasing salinity in the near surface and to decreasing salinity at depth despite tidal transgression monitoring of groundwater levels indicates a phase lag between the tide level and groundwater level supporting the electrical da

evidence for a two phase palmer land event from crosscutting structural relationships and emplacement timing of the lassiter coast intrusive suite antarctic peninsula implications for mid cretaceous southern ocean plate configuration 1 new analysis of the relationships between geological structural data and radiometric ages for the lassiter coast intrusive suite indicate that the collisional mid cretaceous palmer land event orogeny in the antarctic peninsula has had two kinematic phases forming an intersection orocline one of which can be related to cretaceous southern ocean plate motions both are compressional phases along the eastern palmer land shear zone phase 1 occurred at 107 ma with a principal paleostrain axis of 341 and is best expressed in southern palmer land although evident elsewhere on the antarctic peninsula phase 2 occurred at 103 ma with a principal paleostrain axis of 259 5 but is confined to between 68 s and 74 s a peak in lassiter coast intrusive suite magma emplacement rate was coeval with phase 1 whereas phase 2 may have coincided with a lull during phase 1 the allochthonous central and western domain terranes may have been transported to the gondwana margin represented by the para autochthonous eastern domain on board the phoenix plate or on board the south american plate the variable provenance indicators from the central and western terranes can be cited to support either or a combination of these scenarios the convergence direction evident from phase 2 structures cannot easily be reproduced in regional plate kinematic models this and the localized evidence for superposition of phase 2 structures on phase 1 structures suggests that phase 2 is unlikely to have occurred solely in response to changes in the kinematics of the large plates considered

deformation and magnetization of the hudson valley eastern new york results of a study of calcite twinning and anisotropy of magnetic remanence in the onondaga limestone abstract results of a study of calcite twin analysis and anisotropy of anhysteretic remanent magnetization aarm for the onondaga limestone in the hudson valley fold and thrust belt hvb raise questions about the deformation history of this area and the nature of aarm two bedding parallel shortening directions are inferred from calcite twinning one normal to hvb fold axes nw se to ene wsw and the other at high angles to this direction nne ssw to n s two hypotheses are put forward to explain the inconsistent shortening direction 1 even during the initial stages of folding and thrusting in the hvb deformation was three dimensional in character 2 the hvb developed synchronous with main phase alleghanian deformation aarm results are consistent with the magnetic anisotropy being in part caused by the deformation associated with folding and thrusting this is a surprising result because the magnetization is presumably of diagenetic origin and it was acquired after folding

joint sets that enhance production from middle and upper devonian gas shales of the appalachian basin the marine middle and upper devonian section of the appalachian basin includes several black shale units that carry two regional joint sets j1 and j2 sets as observed in outcrop core and borehole images these joints formed close to or at peak burial depth as natural hydraulic fractures induced by abnormal fluid pressures generated during thermal maturation of organic matter when present together earlier j1 joints are crosscut by later j2 joints in outcrops of black shale on the foreland northwest side of the appalachian basin the east northeast trending j1 set is more closely spaced than the northwest striking j2 set however j2 joints are far more pervasive throughout the exposed devonian marine clastic section on both sides of the basin by geological coincidence the j1 set is nearly parallel the maximum compressive normal stress of the contemporary tectonic stress field shmax because the contemporary tectonic stress field favors the propagation of hydraulic fracture completions to the east northeast fracture stimulation from vertical wells intersects and drains j2 joints horizontal drilling and subsequent stimulation benefit from both joint sets by drilling in the north northwest south southeast directions horizontal wells cross and drain j1 joints whenever present then staged hydraulic fracture stimulations if necessary run east northeast i e parallel to the j1 set under the influence of the contemporary tectonic stress field thereby crosscutting and draining j2 joints

case study a 3d resistivity and induced polarization imaging from downstream a waste disposal site in brazil a contaminated site from a downstream municipal solid waste disposal site in brazil was investigated by using a 3d resistivity and induced polarization ip imaging technique this investigation purpose was to detect and delineate contamination plume produced by wastes the area was selected based on previous geophysical investigations and chemical analyses carried out in the site indicating the presence of a contamination plume in the area resistivity model has successfully imaged waste presence 31 mv v water table depth and groundwater flow direction a higher chargeability zone m 31 mv v outside wastes placement and following conductive anomaly was interpreted as a contamination plume normalized chargeability mn m confirmed polarizable zone which could be an effect of a salinity increase contamination plume and the clay presence in the environment

application of induced polarization and resistivity to the environmental investigation of an old waste disposal area waste disposal in dumpsites or even in sanitary landfills can generate contamination plumes in the subsurface the detection and delineation of the shape of the contaminant plume can be assessed using monitoring systems or different site investigation methods including geophysical methods this paper presents the results of a geophysical survey conducted to map the soil contamination produced by a waste disposal site located at a geological vulnerable area characterized by a trench that resulted from the collapse of sandy soils due to erosion this paper aims to show the improvement in mapping a waste deposit and the contamination produced in sandy soils by integrating resistivity and induced polarization methods the results of three survey lines performed to map the site are presented two across the deposit and one external to it and resistivity chargeability and normalized chargeability sections were generated the geoelectrical sections interpretation was integrated with information from monitoring wells to help the characterization of the waste area and to evaluate soil and groundwater contamination the results show that resistivity identifies the wastes the contaminated soil and the contamination plume but it does not distinguish these zones normalized chargeability on the other hand is more effective in distinguishing the areas with wastes from the areas impacted by the contamination plume

dc resistivity mapping of internal landfill structures two pre excavation surveys geophysical investigations using 2 d dc resistivity were carried out on old parts of two similar landfills with waste of different ages the data sets which included high data density in both vertical and horizontal directions were interpreted with 2 d smoothness constrained inversion the landfills were excavated after the surveying the objective was to test the capability of the resistivity method as a pre characterization technique the objectives were only partially fulfilled first the moisture content was the parameter that appeared to exert the dominant control over the resistivity distribution of the landfill the most important potential information that can be recovered is therefore an indication of the waste piles hydraulics second it was neither possible to estimate the amount of recoverable soils nor to correlate the type of waste with the resistivity models however discrete anomalies were identified and if specific materials are searched for the resistivity models indicate possible places to search

deformation history of the nw salient of the eastern ghats mobile belt india abstract the eastern ghats mobile belt of india displays fold thrust belt structure with a prominent salient on its nw margin the salient consists of lathore nappe and turekela klippe that have overthrust the craton to nw the rocks of the nappes have undergone granulite facies metamorphism and multiple phases of folding corresponding to the eastern ghats orogeny prior to thrusting as a result the granulites along the thrust are retrograded to amphibolites and the axial traces of the folds have been truncated against the thrust plane the basal decollement of the fold thrust belt is represented by the terrane boundary shear zone that defines the tectonic margin between the craton and the mobile belt it occurs as a ductile thrust affecting the cratonic basement as well as the mobile belt suggesting that the basement did not behave as a rigid body during thrusting thus the study area is comparable with the caledonide fold thrust belt further two large lateral ramps namely khariar and paikamal lateral ramps have been developed on the decollement at the lithological contact between tonalite trondhjemite gneisses granite gneisses and the latetectonic potassic granites of the craton fault bend folds associate with these ramps too it is suggested that the salient structure of the fold thrust belt is the combined result of 1 lateral ramps on the decollement and 2 differential displacement along the sole thrust due to lateral variation in detachment strength

early jointing in coal and black shale evidence for an appalachian wide stress field as a prelude to the alleghanian orogeny early ene striking joints present coordinates within both pennsylvanian coal and devonian black shale of the central and southern appalachians reflect an approximately rectilinear stress field with a dimension 1500 km this appalachian wide stress field awsf dates from the time of joint propagation when both the coal and shale were buried to the oil window during the 10 15 m y period straddling the pennsylvanian permian boundary the awsf was generated during the final assembly of pangea as a consequence of plate boundary tractions arising from late stage oblique convergence where maximum horizontal stress s h of the awsf was parallel to the direction of closure between gondwana and laurentia after closure the awsf persisted during dextral slip of peri gondwanan microcontinents when sh appears to have crosscut plate scale trans current faults at around 30 sup o following 10 m y of dextral slip during tightening of gondwana against laurentia the awsf was disrupted by local stress fields associated with thrusting on master basement decollements to produce the local orocline shaped alleghanian map pattern seen today

structure of the kingston orocline in the appalachian fold thrust belt new york the trend of the post taconic appalachian fold thrust belt changes at the city of kingston in the new york recess to the southwest of kingston fold thrust structures trend northeast southwest whereas to the north of kingston fold thrust structures trend due north to north northeast this paper discusses the structural geometry and origin of this change in trend detailed mapping 1 9 600 suggests that the fold thrust belt in the vicinity of kingston can be divided into three structural domains northern central and southern in the northern domain megascopic folds are open significant faults do not intersect the present day ground surface ordovician strata below the taconic unconformity are not extensively thrust over post unconformity strata and shortening is less than 5 in the southern domain shortening across the fold thrust belt is 30 numerous faults intersect the ground surface and ordovician strata are significantly thrust over postunconformity strata in the central domain there are numerous accommodation faults there are locally two noncoaxial spaced cleavages and strike slip lineations overprint dip slip lineations on many slip surfaces to explain the contrasts between domains we suggest that the bend at kingston is an intersection orocline created when northeast southwest trending structures of the kittatiny shawangunk segment of the appalachian fold thrust belt overprinted and reoriented older north south trending structures of the hudson valley fold thrust belt calcite twin strain gauge measurements indicate that there was less than 2 penetrative tangential stretching accompanying the development of this orocline

significance of dextral reactivation of an e w transfer fault in the formation of the pennsylvania orocline central appalachians 1 three hypotheses for orocline development including 1 primary plate boundary shape 2 arc rotation and 3 arc overprinting were evaluated for the formation of the pennsylvania orocline maryland usa using foliation intersection inflection axes preserved within porphyroblasts fia the distribution and the timing of sequences of fia data measured from garnet porphyroblasts within the loch raven formation are statistically the same across the pennsylvania orocline suggesting that all subregions of the arc have experienced the same deformation history this may suggest that the geometry of the paleocontinental margin controlled the basic shape of this orocline however if the orocline is treated as three separate regions defined by the sw we ne trending portions of its slightly staircase shaped outline a much higher proportion of the nne ssw trending fias set ii are preserved in the w e trending region than those to either side this geometric relationship could have resulted from wnw ese directed bulk stress causing a zone of dextral shear along what is now the w e trending portion of this orogen it appears that what could have been an early formed w e trending sinistral transform shear zone was preferentially dextrally reactivated during the taconian orogeny

3d behaviour of contamination in landfill sites using 2d resistivity ip imaging case studies in portugal aiming at defining a valid spatial contamination model resistivity and induced polarization ip measurements were used to investigate contamination plumes in the vicinity of two municipal landfills ovar and ilhavo previous geophysical surveys and underground water samples confirmed the contamination however 2d resistivity ip surveys enabled in obtaining a more accurate spatial model the ovar survey consisted of two profiles with nine wenner soundings each the ilhavo survey was carried out along two individual lines using a wenner standard pseudo section in both situations negative ip values were found associated with positive ip values which can be explained mainly by 2d or 3d geometric effects caused by the presence of the conductive plumes the data were modelled using a 2d inversion program res2dinv and the resulting resistivity and chargeability distributions were displayed as pseudo sections the resistivity and chargeability pseudo sections define the contamination plumes and the sedimentary structure these case studies illustrate the advantages of 2d resistivity ip surveys for the mapping of shape and dimension of contamination associated with landfills

characterization of active and closed landfill sites using 2d resistivity ip imaging case studies in penang malaysia an interpretation approach for analysis of electrical resistivity and chargeability inverse models generated at two upgraded semi aerobic landfill sites was developed the inverse models produced from a 2d inversion program res2dinv were used to set up a grid of electrical resistivity and chargeability imaging at the landfill sites the investigations confirmed a high chargeability unit 70 ms depicting waste deposits and a saturated clayey layer while the leachate plume showed low resistivity 10 m and weak chargeability zone 20 ms moreover the ip responses of a diffused leachate plume downstream of a separate semi aerobic landfill site in a similar geological setting were evaluated obtaining an analogous result the ion dominated plume that exhibited a weak chargeability promoted membrane polarization rather than electrode polarization in its ip responses however the high concentration of ions in the diffused leachate restrained the ionic polarization diminishing the ip effects in host sediments the interpretation of the resistivity and chargeability profiles at the characterization sites allowed delineating the different zones of the subsurface strata in particular comparison of the leachate zones at the two locations revealed that the active landfill with a lesser proportion of waste deposits contained a greater accumulation of leachate than the closed site the results in this study support the effectiveness of contaminant plume monitoring through the joint application of resistivity and ip methods these non invasive rapid and cost effective geophysical techniques could lead to a promising reconnaissance tool for remediation or reclamation of solid waste disposal sites

seismotectonics of the explorer region 1 the explorer region offshore western canada is a tectonically complex area surrounded by the pacific north america and juan de fuca plates existing tectonic models for the region differ fundamentally proposed plate configurations range from multiple independent plate fragments to an explorer plate now fused to north america along the continental margin and cut by pacific north america transform faults in the west we present new seismological data constraining the region s current tectonics we use three component regional waveforms to determine the source parameters of 84 earthquakes with magnitude greater than 4 combined with 34 harvard centroid moment tensor solutions they represent the region s largest earthquake source parameter data set obtained by robust waveform modeling techniques in addition we perform joint epicenter determination to relocate larger earthquakes recorded since 1918 the source parameters and improved locations provide a consistent tectonic picture earthquake slip vector azimuths along the pacific plate boundary change smoothly and are significantly less northerly oriented than the pacific north america plate motion direction requiring an independent explorer plate the present day pacific explorer boundary is formed by transform faults subparallel to the revere dellwood wilson fault plate motion vectors indicate that the winona block is part of the explorer plate current explorer motion is more northerly than indicated by magnetic anomalies prior to 2 ma implying a recent change possibly coinciding with a northwestward ridge jump near explorer plate s northern end transferring the winona block from the pacific to the explorer plate in response to these plate motion changes the region north of the western sovanco fracture zone was assimilated into the pacific plate the region around the eastern sovanco fracture zone characterized by broadly distributed seismicity is composed of well defined sets of conjugate faults bounding rotating crustal blocks earthquake fault strikes agree with the dominant northwest southeast fault sets however the conjugate sets must be also active to fully accommodate present day explorer plate motion the sw portion of the strike slip nootka fault zone the explorer juan de fuca plate boundary is well defined by focused seismicity however its full extent under nootka island remains unresolved the explorer north america boundary shows sporadic low magnitude seismicity our explorer north america rotation pole predicts convergence varying from negligible at the boundary s northwest end to 2 cm yr at the se end this convergence can be accommodated either by subduction or by crustal thickening extending to the north american continent we favor subduction based on low deformation rates observed by onshore gps sites the present explorer plate system configuration is a result of stepwise reorientation of the explorer ridge system each step successively reducing the subduction rate relative to north america

two and three dimensional electrical resistivity imaging at a heterogeneous remediation site geometrically complex heterogeneities at a decommissioned sour gas plant could not be adequately characterized with drilling and 2d electrical resistivity surveys alone in addition 2d electrical resistivity imaging profiles produced misleading images as a result of out of plane resistivity anomalies and violation of the 2d assumption accurate amplitude and positioning of electrical conductivity anomalies associated with the subsurface geochemical distribution were required to effectively analyze remediation alternatives forward and inverse modeling and field examples demonstrated that 3d resistivity images were needed to properly reconstruct the amplitude and geometry of the complex resistivity anomalies problematic 3d artifacts in 2d images led to poor inversion fits and spurious conductivity values in the images at depths close to the horizontal offset of the off line anomaly three dimensional surveys were conducted with orthogonal sets of wenner and dipole dipole 2d resistivity survey lines the

structure and origin of the fleurieu and nackara arcs in the adelaide fold thrust belt south australia salient and recess development in the delamerian orogen abstract the regional map pattern of structural trends in the early paleozoic adelaide fold thrust belt of south australia resembles an upright letter s in general structures in the fold thrust belt verge toward the gawler craton to the west so the northern curve nackara arc of the s is a salient whereas the southern curve fleurieu arc is a recess the map view axial trace of the nackara arc coincides with the thickest portion of the adelaidean late proterozoic basin and the map view axial trace of the fleurieu arc coincides with the intersection between the adelaidean and kanmantoo cambrian basins our structural analysis of the adelaide fold thrust belt demonstrates that the cross sectional structural geometry of the nackara arc contrasts markedly with that of the fleurieu arc in the nackara arc the belt consists of open detachment folds that probably formed above an evaporite hosted decollement whereas in the fleurieu arc the belt consists of an imbricate fan of basement involved thrusts further the foreland edge of the nackara arc coincides with a blind ramp whose strike parallels fold axes of the arc whereas the foreland edge of the fleurieu arc coincides with emergent thrusts that cut obliquely across earlier formed folds of the arc in the transition region between the two arcs the fold thrust belt consists of an intensely sheared basal duplex overlain by open folds structural contrasts between the nackara and fleurieu arcs indicate that the two curves did not form in the same way we present a model for development of these curves based on a comparison of their structural features to those of curves in other fold thrust belts and based on previous studies of curve formation using sandbox analogs we suggest that curvature of the nackara arc reflects the control of basin stratigraphy on the width of a fold thrust belt while curvature of the fleurieu arc reflects oroclinal bending of the fold thrust belt when it impinged on the southeastern corner of the gawler craton our model explains the structural contrast between the two arcs and illustrates correlations between fold thrust belt curve formation and pre deformational basin geometry

factors controlling slip lineation orientation on thrust fault planes abstract the presence of multiple sets of curved and or non coaxial slip lineations on a single fault surface suggests changing stress conditions during the movement history of the fault curved slip lineations suggest a progressive change in the stress field during a single displacement event whereas non coaxial slip lineations suggest periodic reactivation of a fault under different stress conditions if the direction of slip is assumed to reflect the direction of maximum shear stress acting on a pre existing fault changes in only the relative magnitudes of principal stresses acting on the thrust sheet are sufficient to cause changes in slip lineation orientation consequently curved and or non coaxial slip lineations simply may record temporal changes in principal stress magnitudes resulting from syntectonic erosion changes in tectonic stress magnitude and ramping of thrusts to shallower depths we illustrate that a decrease in overburden or an increase in the magnitude of tectonic stress results in a progressive up dip rotation of slip lineations on a fault surface a rotation which could be misinterpreted as indicating polyphase deformation caused by changes in regional displacement directions changes in pore pressure do not influence the trajectory of slip on a fault surface but rather affect the conditions governing the likelihood for slip to occur

deformation of the proterozoic somanpalli group pranhita godavari valley south india implication for a mesoproterozoic basin inversion abstract the proterozoic somanpalli group originally deposited in a nw se trending fault controlled basin in the pranhita godavari valley pg valley suffered contractional deformation as recorded in nw se trending large scale folds imbricate thrusts second order semibrittle shear zone and smaller folds faults and cleavage three distinct structural stages dominated respectively by folding thrusting and strike slip faulting in that order can be recognized from overprinting relationships in outcrops the local ene wsw fold axis azimuth and cleavage strike is related to variation in the original depositional strike controlled by e w transfer faults rejuvenated as sinistral strike slip zones during the main contractional deformation a late extensional event possibly occurring during the upper proterozoic or mesozoic gondwana has been superimposed locally on the earlier fabric of the fold thrust belt the nw se trending folds and thrusts in the somanpalli group demonstrate the presence of a hitherto unrecognised compressional regime records of which occur in a 200 km stretch along the eastern margin of the pg valley the somanpalli group may be correlated with the mesoproterozoic pakhal group 1350 ma since the former is overlain by grossly undeformed and unmetamorphosed rocks of the neoproterozoic sullavai group a mesoproterozoic basin inversion in this region is suggested

possible mesozoic age of ellenville zn pb cu ag deposit shawangunk mountains new york ore textures epithermal open space filling of permian structures of the alleghanian orogeny and largely postorogenic mineralization of the ellenville new york composite zn pb cu ag vein system provide permissive evidence for post permian mineralization isochron ages determined by 40ar 39ar laser fusion techniques for k bearing liquid inclusions in main stage quartz from the ellenville deposit additionally suggest a mesozoic time of mineralization associated with extensional formation of the newark basin the best 40ar 39ar total fusion age range is 165 30 to 193 35 ma the mesozoic 40ar 39ar age agrees with that of many other dated northern appalachian zn pb cu ag deposits with near matching lead isotope ratios and adds new evidence of jurassic tectonism and mineralization as an overprint to late paleozoic tectonism at least as far north as ellenville lat 41 43 n

basalt geochemistry of the explorer ridge area northeast pacific ocean forty two fragments of young fresh basalts dredged from the explorer ridge paul revere ridge fracture zone and dellwood knolls have been analysed for 34 major minor and trace elements and 87sr 86sr ratios have been determined in seven of the fragments the explorer ridge basalts have major element compositions similar to most mid ocean ridge basalts morb particularly to the iron rich basalts of the southern juan de fuca ridge the basalts exhibit variability in trace element content largely attributable to crystal fractionation at low pressure with respect to morb the incompatible minor and trace elements are weakly to strongly enriched in the explorer samples and are most strongly enriched in basalts from explorer deep adjacent ridge segments erupt basalts with variable incompatible element concentrations and ratios this could be an indicator of a chemically heterogeneous mantle source or may be the result of intermittent injection of enriched magmas from a hotspot beneath explorer deep

comparison of fry strain ellipse and ams ellipsoid trends to tectonic fabric trends in very low strain sandstone of the appalachian fold thrust belt abstract in moderately to highly strained sandstones both the long axis of the bedding parallel finite strain ellipse as calculated by the normalized fry method and the projection of the long axis of the ams ellipsoid on the plane of bedding align well with local structural grain trends of cleavage folds and faults this relationship implies that results of both 2d fry and ams analyses represent the local layer parallel tectonic strain component do both methods provide comparable results for very low strain sandstone e g

deformation history of the roanoke recess appalachians usa the evolution of the roanoke recess is controversial because agreement is lacking about the timing and continuity of deformation increments because it may or may not have behaved like an adjacent salient and recess because while many salients have been investigated few recesses have and because the role of blind thrusts is unclear to gain insight into these controversies we estimated shortening directions shortening magnitudes and relative timing in the recess from map scale folds outcrop scale stylolites and grain scale solution structures and twins the key results from combining these new data with previous work are as follows 1 the deformation history around the roanoke recess is most simply described as temporally continuous with deformation migrating northeastward while the primary shortening direction rotated counterclockwise from n directed to almost w directed 2 consequently the roanoke recess did not deform in the symmetrical manner of the adjacent pennsylvania salient nor with the two step history of the kingston recess further to the north in the appalachians 3 the timing and magnitude of shortening increments are sufficient to necessitate a blind thrust under the present surface rocks of the inner recess throughout the deformation history

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

a 3 d resistivity investigation of a contaminated site at lernacken sweden a contaminated site at lernacken in southern sweden formerly used for sludge disposal was investigated using a 3 d resistivity imaging technique the data acquisition was carried out using a roll along technique for 3 d data acquisition that allows using standard multielectrode equipment designed for engineering and environmental applications the technique allows for the measurement of large true 3 d resistivity data sets and data were measured using two perpendicular electrode orientation directions with only one layout of the cables the data were plotted as two sets of pseudo depth slices using the two electrode orientation directions which resulted in markedly different plots the complete data set was inverted to form a resistivity depth model of the ground using a 3 d least squares smoothness constrained inversion technique the results obtained were compared to other geophysical and background data and a good agreement was found the results show that the 3 d roll along technique in combination with 3 d inversion can be highly useful for engineering and environmental applications however multichannel measurement equipment is necessary to speed up the data acquisition process for routine application

stress origins and earthquake potentials in cascadia focal mechanism solutions for shallow earthquakes throughout the cascadia plate system indicate that the primary regional stress is northerly compression even though the juan de fuca plate generally is thought to be subducting n50 e this compressional stress is pervasive throughout the gorda juan de fuca explorer plate system and much of the adjoining section of north american plate modeling using a discrete element code shows that this stress primarily is due to the pacific plate being driven into the gorda block and juan de fuca plate at the mendocino and blanco fracture zones this plate collision causes compression of the offshore plate system northward through the 45 w trending vancouver island and leads to transfer of northerly compression into the overriding plate the northerly compression in the cascadia plate system has caused large crustal earthquakes in the regions of vancouver and northern california and may be capable of causing large earthquakes also in and offshore of washington and oregon several independent lines of evidence confirm that the cascadia subduction interface is coupled strongly and that subduction primarily must be accompanied by significant earthquakes rather than occurring aseismically for numerous earthquakes within the subducted plate focal mechanisms indicate extensional stresses that trend downdip these earthquakes reflect plate extension that is due to sinking of the more deeply subducted plate and to plate motion being resisted at the shallow subduction interface the slab pull force of the sinking plate also can lead to earthquakes at the shallow subduction interface and the potential exists for m 7 5 8 0 subduction earthquakes to occur at segments of the subduction boundary at washington and vancouver and less frequently so at segments of the subduction boundary at oregon the in plate driving forces of the offshore cascadia plate system do not appear to contribute significantly to regional stresses stresses and earthquakes at the cascadia province primarily result from the action of the pacific plate on the gorda juan de fuca explorer plate system a transfer of this action into the overriding north american plate and the independent sinking and slab pull force of the subducted oceanic lithosphere

seismicity and rates of relative motion on the plate boundaries of western north america summary the consistency of earthquake data and plate tectonic models and other estimates of fault slip may be tested by estimating rates of motion from the earthquakes using the concept of seismic moment the contribution of individual events may simply be summed but a generally better estimate of long term average slip rate is obtained by integration over magnitudefrequency of occurrence relations estimates of fault motion rates associated with earthquakes are possible within about a factor of 2 using this approach if the major sources of uncertainty are given careful consideration e g incompleteness and inaccuracies in the earthquake data empirical moment magnitude relations and the effect of their stochasticity fault widths or depth extents the recurrence relations maximum magnitudes and the form of truncation at the maximum magnitude a formulation for the recommended magnitude density truncation is developed application of the latter method to the earthquake data of the offshore transform faults of the juan de fuca ridge system the queen charlotte fault zone and the northern vancouver island area in each case gives good agreement with rates from plate tectonic models for the southern san andreas fault and gulf of california area there is also good agreement with previous estimates obtained by summing the contributions of individual events however the displacement rate in the margin convergence zone of southern british columbia washington and oregon computed from the seismicity is at least a factor of 10 lower than from plate models and from other convergence estimates and primarily aseismic slip is suggested the fault motions as a function of time computed from the seismicity records have also been plotted and compared to the longterm average rates the plots permit estimates of the minimum present accumulated elastic strain and show if there are any temporal relations among earthquake displacements on different fault zones

orocline timing through joint analysis insights from the ibero armorican arc abstract the timing and kinematics of oroclinal bending in the core of the ibero armorican arc iaa has recently been constrained using paleomagnetic data from the cantabrian zone in northern iberia this study analyzes the joint patterns present in rock units deposited pre syn and post oroclinal bending systematic changes in the orientations of tensional joint sets in superimposed stratigraphic units are interpreted to record the progressive stages of oroclinal bending in the core of the iaa time constrains for joint set development are constrained by the known ages of the bounding unconformities that limit the studied stratigraphic units joint azimuth variability in the pre orocline rocks neoproterozoic to pre upper carboniferous is comparable to the present arc curvature of the orocline about 180 the joints in the syn orocline rocks upper pennsylvanian or stephanian 304 to 299 ma show a lower azimuthal variability that is comparable to about 50 70 of the total curvature seen in pre orocline rocks finally post orocline rocks permian contain joints that have uniform azimuths for each set across the entirety of the present day arc together these spatially and temporally distinct joint sets suggest that rotations in the cantabrian zone took place in the upper pennsylvanian during a ca 10 ma time period which agrees well with previous paleomagnetic arguments the data also provides supporting evidence for oroclinal bending by rotation around vertical axes of an initially linear or nearly linear orogenic belt and finally these data highlight the potential power in using tectonic joint sets for constraining thrust belt kinematics in curved orogenic systems when unconformity bounded stratigraphic sequences are present that are coeval with orocline development

integrated earth resistivity tomography ert and multilevel sampling gas a tool to map geogenic and anthropogenic methane accumulation on brownfield sites soil gas emissions of methane and carbon dioxide on brownfield sites are usually attributed to anthropogenic activities however geogenic sources of soil gas are often not considered during site investigation and risk management strategies this paper presents a field study at a redeveloped brownfield site on a flood plain to identify accumulations of methane biogas trapped in underlying sediments the investigation is based on a multidisciplinary approach using direct multi level sampling measurements and earth resistivity tomography resistivity imaging was applied to evaluate the feasibility of identifying the size and spatial continuity of soil gas accumulations in anthropogenic and naturally occurring deposits as a result biogas accumulations are described within both anthropogenic deposits and pristine organic sediments this result is important to identify the correct approaches to identify and manage risks associated with soil gas emissions on brownfield and pristine sites the organic rich sediments in quaternary fluvial environments of sao paulo basin in particular the tiete river biogas reservoirs can be generated and trapped beneath geogenic and anthropogenic layers potentially requiring the management of brownfield developments across this region