the effect of earth rheology and ice sheet size on fault slip and magnitude of postglacial earthquakes abstract moderate past and present day seismicity is observed in formerly deglaciated regions of north america and europe an understanding of the occurrence of these earthquakes is important for estimating the seismic risk within these areas as well as areas affected by recent ice sheet melting in particular greenland and antarctica we have developed a new finite element approach that allows us to estimate the fault throw for areas once covered by a continental ice sheet the simulation is initialized by loading a two dimensional earth model with an ice sheet the model incorporates a stress field consisting of rebound horizontal background and vertical stresses as well as a fault that can accommodate slip the sensitivity of fault throw and activation time is tested with respect to lithospheric and crustal thickness viscosity structure of upper and lower mantle and ice sheet thickness and width as well as fault location and angle single event seismic displacements of up to 18 5 m are obtained approximately equivalent to an earthquake with a moment magnitude of 8 5 the thickness of the crust and lithosphere are major parameters affecting the total magnitude of fault slip whereas the size of the ice sheet primarily affects the activation time most faults start to move close to the end of deglaciation and movement typically stops for our simulations after one thrusting reverse earthquake however in our simulations faults with a dip of 60 also show several fault movements before and after the end of deglaciation

the dibdibba aquifer system at safwan zubair area southern iraq hydrogeology and environmental situation the objective of this research is to study the environment and hydrogeology of the dibdibba aquifer system in the safwan zubair area southern iraq in relation to the study area s geology and anthropogenic activities ten groundwater samples were collected from safwan zubair geochemical data aquachem and gis arcmap 10 1 were used as tools to identify natural and anthropogenic factors that affect geochemical data we analyzed water samples for major cations and anions polycyclic aromatic hydrocarbons pahs total uranium tu and heavy metals pb ni cr cd v zn as se cu fe mn as well as the metalloid b groundwater composition in the area of study is classified into six types ca mg cl ca mg na cl ca mg cl so4 ca mg na cl so4 ca na mg so4 cl and mg ca cl so4 the groundwater is influenced by natural factors particularly the concentrations of tu and major ions the concentrations of tu and major ions in some water samples exceed limits for drinking water however the average of all examined heavy metals except for fe and b was within the limits for drinking water as well as the concentrations of pahs the potential use of this groundwater for drinking and irrigation is discussed

the greenland earthquake of 11 july 1987 and postglacial fault reactivation along a passive margin abstract intraplate earthquakes in many cases occur near continental margins this observation applies very well to the case of greenland a stable continental region with low seismicity the seismicity of greenland is nearly totally concentrated along the coastlines of the island where it is relatively free of ice cover on 11 july 1987 the largest greenland earthquake of instrumental record m b 5 5 m w 5 4 occurred in continental crust off the northeastern coast in the wandel sea waveforms of long and short period teleseismic p and long period teleseismic sh waves have been modeled to estimate the source parameters for this earthquake the focal mechanism determined is a normal faulting with a strike slip component strike 148 dip 59 and rake 131 the strike direction of one of the nodal planes was found to be consistent with the direction of the dominant structural trend observed in the area a previous normal faulting mechanism with very different strike directions for this event was found to have inferior waveform fit and is not consistent with the fault strike directions from the local geological setting the seismic moment of the july 1987 earthquake is 1 75 10 24 dyne cm the focal depth and stress drop are 5 km and 389 bars respectively the high stress drop may relate to the relatively long earthquake repeat time in the region the observed normal faulting of this earthquake can be interpreted as a rupture due to an extensional stress field at the forebulge outside of the ice sheet because of deglaciation flexure in the region another major earthquake 26 november 1971 m b 5 1 311 km to the south of the 11 july 1987 event was likewise determined to be normal faulting and can be explained as another event triggered by deglaciation in addition we find that the sparse general seismicity of greenland can also be related to postglacial rebound

stress field constraints on intraplate seismicity in eastern north america focal mechanisms of 32 north american midplate earthquakes mo 3 8 6 5 were evaluated to determine if slip is compatible with a broad scale regional stress field derived from plate driving forces and if so under what conditions stress regime pore pressure and frictional coefficient using independent information on in situ stress orientations from well bore breakout and hydraulic fracturing data and assuming that the regional principal stresses are in approximately horizontal and vertical planes 10o the constraint that the slip vector represents the direction of maximum resolved shear stress on the fault plane was used to calculate relative stress magnitudes defined by the parameterb s2 s3 s s3 from the fault stress geometry as long as the focal mechanism has a component of oblique slip i e the b axis does not coincide with the intermediate principal stress direction this calculation identifies which of the two nodal planes is a geometrically possible slip plane gephart 1985 slip in a majority of the earthquakes 25 of 32 was found to be geometrically compatible with reactivation of favorably oriented preexisting fault planes in response to the broad scale uniform regional stress field slip in five events was clearly inconsistent with the regional stress field and appears to require a localized stress anomaly to explain the seismicity significantly all five of these events occurred prior to 1970 when many regional networks were installed and their focal mechanisms are inconsistent with more recent solutions of nearby smaller events the frictional likelihood of the geometrically possible slip on the selected fault planes was evaluated in the context of conventional frictional faulting theory the ratio of shear to normal stress on the fault planes at hypocentral depth was calculated relative to an assumed regional stress field regional stress magnitudes were determined from 1 s s3 ratios based on the frictional strength of optimally oriented faults the basis for the linear brittle portion of lithospheric strength profiles 2 the computed relative stress magnitude b values and 3 a vertical principal stress assumed equal to the lithostat two end member possibilities were examined to explain the observed slip in these less than optimally oriented fault planes first the frictional coefficient was held constant on all faults hydrostatic pore pressure was assumed regionally and the fault zone pore pressure was determined since pore pressure is a measurable quantity with real limits in the crust p0 s3 this end member case was used to determine which of the geometrically possible slip planes were frictionally likely slip planes alternately pore pressure was fixed at hydrostatic everywhere and the required relative lowered frictional coefficient of the fault zone was computed slip in 23 of the 25 geometrically compatible earthquakes was determined to also be frictionally likely in response to an approximately horizontal and vertical regional stress field derived from plate driving forces whose magnitudes are constrained by the frictional strength of optimally oriented faults assuming hydrostatic pore pressure regionally the conditions for slip on these 23 relatively well oriented earthquake faults were determined relative to this regional crustal strength model and require only moderate increases in pore pressure between about 0 4 0 8 of lithostatic hydrostatic is about 0 37 of lithostatic or alternately moderate lowering 50 of the frictional coefficient on the faults which slipped superlithostatic pore pressures are not required focal mechanisms for the two other earthquakes with slip vectors geometrically consistent with the regional stress field however did require pore pressures far exceeding the least principal stress or extremely low coefficients of friction these events may reflect either local stress rotations undetected with current sampling or poorly constrained focal mechanisms the analysis also confirmed a roughly north to south contrast in stress regime between the central eastern united states and southeastern canada previously inferred from a contrast in focal mecha nisms between the two areas most central eastern united states earthquakes occur in response to a strike slip stress regime whereas the southeastern canadian events require a thrust faulting stress regime this contrast in stress regime with a constant maximum horizontal stress orientation determined by far field plate driving forces requires a systematic lateral variation in relative stress magnitudes superposition of stresses due to simple flexural models of glacial rebound stresses are of the correct sense to explain the observed lateral variation but maximum computed rebound related stress magnitude changes are quite small about 10 mpa and do not appear large enough to account for the stress regime change if commonly assumed stress magnitudes determined from frictional strength apply to the crust at seismogenic depths

deformation maps in grain size stress space as a tool to investigate mantle rheology abstract deformation maps have found widespread use in the study of the rheology of earth materials the usual procedure is to construct a map in stress temperature space from which predominant creep mechanisms strain rates and viscosities can be determined for a given grain size the rheology of polycrystals however depends strongly on grain size and consequently a fuller description would entail the construction of three dimensional stress grain size temperature diagrams as these do not display clearly the parameters of interest it is proposed to use deformation maps in stress grain size space at a given temperature in several situations of geodynamic interest grain size is a more critical parameter than temperature furthermore stress grain size maps have the advantages of simplicity and clarity for instance the boundaries between nabarro herring coble and power law creep are straight lines and so are constant strain rate and constant viscosity contours the triple point at which the three boundaries converge is under reasonable assumptions a function of temperature only and the slopes of the boundaries are independent of temperature it is therefore possible to project on a single map data for various temperatures the coordinates of the triple point contain all the necessary information for a synoptic representation of the rheology as an example deformation maps in stress grain size space are presented for olivine under laboratory and upper mantle conditions

the geology of the steenkampskraal monazite deposit south africa implications for ree th cu mineralization in charnockite granulite terranes the ca 1100 ma namaqualand metamorphic complex is host to a number of vein type monazite apatite chalcopyrite magnetite deposits which cluster in a approximately 30 km 2 area 160 km south of the okiep copper district the largest of these veins at steenkampskraal has been mined intermittently since the late 1950s for thorium field relationships demonstrate that the monazite apatite vein of steenkampskraal is parallel to a sheared cuspate anticline strikingly similar to the well known steep structures of the okiep copper district quartz diorite and leucotonalite are found at the core of the anticline in direct contact with the monazite apatite vein and comprise the newly proposed roodewal suite this association is also represented by veins and or dikes of anorthosite norite enderbite and charnockite that have a regional distribution in the steenkampskraal area textural relationships indicate that monazite and orthopyroxene coexist in the charnockite veins and that monazite may be a minor constituent of the quartz diorite electron microprobe analyses of monazite from steen kampskraal and other localities display high tho 2 contents 8 8 8 wt whereas bulk rock ree analyses demonstrate a strong depletion in eu and high la yb ratios sm nd isotope data for the monazite ore and closely associated rocks indicate model ages of 1010 to 1278 ma chondritic uniform reservoir mantle chur or 1450 to 1770 ma depleted mantle resevoir dm the chur model age is preferred as it compares to a published u pb age of 1180 or 40 ma and to our new whole rock u pb age for the ore of 1150 or 15 ma age relationships coupled with the coexistence of orthopyroxene and monazite provide evidence that the mineralized veins of the newly proposed steenkampskraal monazite district formed under water undersaturated conditions in granulite facies t approximately 800 degrees 860 degrees c p approximately 5 6 kbars a finding inconsistent with the previously proposed hydrothermal model the new findings may indicate that the monazite apatite ore was deposited by h 2 o deficient mineralizing fluids of crustal metamorphic or mantle origin however the lithological mineralogical and structural features of the steenkampskraal monazite deposit resemble those of the silica poor magnetite ilmenite apatite rich rocks nelsonite of the koperberg suite in the okiep copper district although age of intrusion sm nd isotope systematics and composition of the mineralization present clear differences for the two areas the structural style and associated intrusive rocks of the roodewal and koperberg suites are very similar protracted fractionation of a rare metals enriched magma yielding anorthositic cumulates and p rich immiscible liquids is therefore proposed as a model for the steenkampskraal deposit and for the nelsonitc occurrences in the okiep copper district the ores of the steenkampskraal monazite district may consequently represent a separate class of polymetallic rare earth element ree mineralization with possible equivalents in other high grade terranes such as in madagascar in mozambique and in the southeastern united states

depth of penetration of lubricant fluids and water in queenston shale of southern ontario queenston shale is a rock formation located in southern ontario in canada that exhibits time dependent deformation behaviour induced by water penetration microtunnelling is an efficient technique that can be used to construct pipelines and tunnels in queenston shale in this technique lubricant fluids such as bentonite solution and polymer solution are utilized which can have a significant impact on the time dependant deformation i e swelling of queenston shale within their depth of influence a test procedure was developed in this research to investigate the depth of penetration of lubricant fluids and water in queenston shale these fluids were applied under pressure similar to that used in the microtunnelling process on queeenston shale specimens the depth of penetration of these fluids into the test specimens was monitored with time it was concluded that the penetration depth varied for the various fluids considered water had the deepest penetration into queenston shale based on the obs

osmotic model to explain anomalous hydraulic heads laboratory experiments have shown that compacted clays act as osmotic membranes when they separate aqueous solutions of unequal ionic concentration theoretically osmotically induced differential hydraulic pressure in groundwater systems can be relatively high the magnitude depends primarily upon concentration differences across the membrane type of ions type of clay and pore size in experiments thin compacted clay membranes commonly exhibit varying degrees of osmotic efficiency due to ion leak age through the clay in natural systems the membrane and the solution containers are not as distinct and well defined as they are in the laboratory moreover the membrane is commonly thick inhomogeneous and composite in a buried triassic basin at the savannah river plant near aiken south carolina it is suspected that osmosis causes the saline water in the basin center to be slightly geopressurized in relation to freshwater in the overlying coastal plain aquifer two wells have heads of 7 88 and 12 98 bars 114 3 and 188 3 psi above the head in the coastal plain aquifer the head in each of these wells approximates the osmotic equilibrium head calculated from solution concentration of water produced by each well 12 000 and 18 500 mg l respectively other wells penetrating the top and edge of the triassic basin probably penetrate a zone where ion leakage gives rise to less saline water thus these wells are not geopressurized

groundwater recharge history and hydrogeochemical evolution in the minqin basin north west china the minqin basin is a type area for examining stress on groundwater resources in the gobi desert and has been investigated here using a combination of isotopic noble gas and chemical indicators the basin is composed of clastic sediments of widely differing grain size and during the past half century over 10 000 boreholes have been drilled with a groundwater decline of around 1 m a 1 modern diffuse recharge is unlikely to exceed 3 mm a 1 as determined using unsaturated zone profiles and cl mass balance a small component of modern 50 a groundwater is identified in parts of the basin from 3h 3he data probably from irrigation returns a clear distinction is found between modern waters with median 18o values of 6 5 0 5 and most groundwaters in the basin with more depleted isotopic signatures radiocarbon values as pmc range from 0 6 to 85 modern but it is difficult to assign absolute ages to these although a value of 20 modern c probably represents the late pleistocene to holocene transition the 13c compositions remain near constant throughout the basin median value of 8 1 13c and indicate that carbonate reactions are unimportant and also that little reaction takes place there is a smooth decrease in 14c activity accompanied by a parallel increase in 4he accumulations from s n across the basin which define the occurrence of a regional flow system noble gas temperatures indicate recharge temperatures of about 5 6 c for late pleistocene samples which is some 2 3 c cooler than the modern mean annual air temperature and the recharge temperature obtained from several holocene samples groundwaters in the minqin basin have salinities generally below 1 g l and are aerobic containing low fe but elevated concentrations of u cr and se mean values of 27 5 5 8 and 5 3 g l 1 respectively nitrate is present at baseline concentrations of around 2 mg l 1 but there is little evidence of impact of high no3 from irrigation returns strontium isotope and major ion ratios suggest that silicate reactions predominate in the aquifer the results have important implications for groundwater management in the minqin and other water stressed basins in nw china a region so far destined for rapid development the large proportion of the water being used at present is in effect being mined and significant changes are urgently needed in water use strategy

re visiting the tectonics of the oceanic intraplate earthquake of march 25 1998 m 8 1 in the balleny sea offshore antarctica abstract the antarctic plate earthquake of march 25 1998 m 8 1 and its aftershocks are re visited to evaluate the role of the associated tectonics in stress concentration due to ambient horizontal crustal motion caused by deglaciation in antarctica using a numerical technique called the distinct element method a two dimensional structural model of the epicentral region is developed and tectonically loaded for a year along the inferred direction of the motion a spatial correlation is observed between the resulting locations of relatively high shear stresses and those of the main shock and associated aftershocks in particular seismicity is concentrated at and near the intersections of the main fault carey and gambier fracture zones where the shear stresses are significantly elevated and whose sign duplicate the inferred sense of movement along them the modeling results suggest that stress concentrations near pre existing intersecting fault and fracture zones due to a possible deglaciation induced horizontal crustal force may have been a cause of this enigmatic earthquake

postglacial rebound and the focal mechanisms of eastern canadian earthquakes a detailed numerical model of postglacial rebound for the eastern canadian arctic is described with special attention being paid to baffin island this numerical model is able to account for the observed uplift patterns as recorded by the relative sea level histories of discrete sites distributed throughout the study area these uplift patterns show regional trends so the same model can be used to interpolate between data sites and to estimate the uplift history at any arbitrary site within the study area by treating the lithosphere as a thin elastic plate spatial variations in the uplift pattern can be translated into estimates of lithospheric stress the model predicts the variations in uplift as a function of both space and time since deglaciation and can therefore be used to estimate the temporal evolution of lithospheric stress following deglaciation the stress so calculated is treated as a perturbation to an ambient stress field having its origin in other processes postglacial rebound is shown to

seismotectonics of northeastern united states and adjacent canada data for local earthquakes recorded by a network of stations in northeastern united states and adjacent canada were analyzed to study the seismicity the relationship between earthquakes and known faults the state of stress and crustal and upper mantle velocity structure in addition portable seismographs were deployed in the field to study aftershocks as a result accurate locations for about 364 local earthquakes 2 mb 5 and 22 focal mechanism solutions were determined a comparison of the spatial distribution of these events 1970 1979 with historical earthquakes 1534 1959 reveals that seismic activity in the northeast is relatively stationary in space those areas that have had little or no seismicity historically are relatively aseismic today whereas the historically active areas are also active today the instrumental locations historical seismicity and focal mechanism solutions show an internal consistency that help us distinguish two distinct seismogenic provinces 1 the adirondack western quebec province is a northwesterly trending zone of seismic activity about 200 km wide and at least 500 km long extending from the se adirondacks into western quebec canada thrust faulting on planes striking nnw to nw appears to predominate and the inferred axis of maximum horizontal compression is largely uniform and trends wsw nearly parallel to the calculated absolute plate motion of north america little or no seismicity is found where anorthosite outcrops at the surface correlations between gravity anomalies and earthquake locations suggest that seismic activity in this zone is localized to regions of steep ne or sw gradient in bouguer anomalies this zone does not appear to extend southeastward to boston as proposed by some workers 2 the appalachian province is a northeasterly trending zone of seismic activity extending from northern virginia to new brunswick canada highangle reverse or thrust faulting on n to ne trending planes appears to predominate the western margin of this province however appears to be relatively aseismic we attribute this relative lack of activity to one or more of the following the presence of igneous activity postdating rifting of africa from north america the occurrence of intense metamorphism during the acadian orogeny which may have annealed preexisting faults and the predominance of ductile as opposed to brittle deformation in the geologic past the inferred axis of maximum horizontal compression along the eastern margin of the appalachians is rather uniform and trends w wnw almost perpendicular to the magnetic lineations offshore we suggest that this w wnw compression reflects the gravitational force arising from horizontal density variations in the oceanic lithosphere as it cools and moves away from spreading centers

gravity induced soft sediment deformation in glaciomarine sequences of the upper proterozoic port askaig formation scotland large numbers of post depositional deformation structures in the form of downward penetrating sandstone bodies are identified on well exposed diamictite surfaces of the glaciogenic upper proterozoic port askaig formation scotland on the garvellach islands downfolds irregular dykes and a polygonal network of wedges are composed predominantly of massive fine to medium grained sandstone these structures occur towards the top of crude coarsening upward glaciomarine sequences of massive diamictite stratified diamictite variably cross stratified sandstone and conglomeratic lags massive diamictites record the dominance of pelagic sedimentation and ice rafting succeeding lithofacies indicate the increasing importance of marine traction currents these sequences are repeated in the port askaig formation and by comparison with late cenozoic glaciomarine sequences may have formed in response to changing water depths during basin subsidence downfolds dykes and a polygonal wedge network appear to be genetically related expressions of subaqueous gravitational loading and intrusion of sand into low strength diamict acting in response to reverse density gradients created by coarsening upward glaciomarine sedimentation analogues are provided by published laboratory investigations analysis of the regional tectonic setting of the formation suggests the importance of seismic shock as a triggering agent the subaqueous deformation model presented in this paper is of considerable significance for reconstruction of late proterozoic palaeoenvironments because the downward penetrating sandstone structures of the port askaig formation are widely reported to be indicative of the former presence of subaerial permafrost this paper stresses the importance of identifying the lithofacies sequence in which structures occur as a guide to deformational environment

four seismogenic environments in eastern canada abstract although the seismogenic environments in eastern canada have some common features the respective seismotectonic environments are influenced by local features the seismotectonic environment in four seismogenic regions are described in order to illustrate how local features are reacting with the ambient plate tectonic stress a common feature to modify the nature of the seismic activity the charlevoix earthquakes are occurring along steeply dipping planes formed during the opening of lapetus ocean in the proterozoic perturbed by a meteor impact during the paleozoic and reactivated by the opening of the present day atlantic ocean in the mesozoic theoretical curves of maximum shear stress versus depth based on a wet upper crust and a wet quartz rheology in the lower crust for which the heat flow is 1 0 hfu 42 mw m2 can account for the depth distribution of earthquakes in this region potential trigger mechanisms are gravitationally induced stress water infiltration and vertical shear strain changes approximately 3 10 8 yr due to post glacial rebound the unusually deep focus 29 km of the m 5 9 saguenay earthquake of 1988 could be due in part to the lower heat flow in this region as compared with that in the charlevoix region which is about 70 km to the east the miramichi earthquake sequence is occurring on conjugate faults within an intrusion at depths shallower than 10 km theoretical curves of maximum shear stress versus depth based on a wet quartz rheology in the lower crust for which the heat flow is 1 5 hfu can account for this depth distribution the steep gradient in the vertical ground movement rate 5 10 8 yr in the epicentral area which is probably due to post glacial rebound is a potential trigger mechanism for favorably oriented faults the normal fault seismic regime along northeastern baffin island can be explained by a combination of topography and post glacial rebound which can generate horizontal extensional stresses capable of overcoming the ambient compressional plate tectonic stress post glacial rebound stress can act as a trigger mechanism for the ne dipping faults in this region in the grand banks region there is seismic evidence indicating that the slump that caused the destructive tsunami also generated the strong seismic m 7 2 signals but double couple solutions that satisfy certain criteria are not ruled out the absence of surface faulting especially in the epicentral regions of large earthquakes is not properly understood but several possibilities are near surface layering that could mask the underlying fault offsets and a spatiotemporal variation in the ambient plate tectonic stress field as knowledge of the causative factors of eastern canada earthquakes and also the data base for empirical earthquake scaling relations increase an overview of the seismotectonics of these mid plate earthquakes should be enhanced

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

viscoelastic membrane tectonics the theory of membrane tectonics proposed by turcotte and oxburgh 1973 to explain intraplate tensional features and earthquakes and developed by turcotte 1974 for an elastic lithospheric membrane is extended to the case of a viscoelastic lithosphere such an extension may be expected to seriously modify the theory since for all lithospheric viscosities except the very highest the time scale for viscous relaxation is comparable to the time scale for changes in plate curvature it is found that for most viscosities considered the membrane stresses generated by changes in plate curvature do not exceed 10 bars we conclude that either the effective viscosity of the lithosphere is much higher than indicated by most studies or membrane tectonic stresses play a secondary role in the generation of intraplate features and earthquakes

late cretaceous to recent tectonic evolution of the north german basin and the transition zone to the baltic shield southwest baltic sea abstract in this study we investigate the late cretaceous to recent tectonic evolution of the southwestern baltic sea based on a dense grid of seismic reflection profiles this area covers the baltic sea sector of the salt influenced north german basin and its transition to the salt free baltic shield across the tornquist zone the upper cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high resolution time structure maps of the main horizons i e the upper cretaceous tertiary and pleistocene the upper cretaceous and tertiary layers reveal numerous significant faults throughout the study area several of these faults propagate upwards across the unconsolidated pleistocene sediments and occasionally penetrate the surface the salt influenced north german basin reveals three major fault trends nw se n s and nne ssw several of these faults are located directly above basement sub salt faults and salt pillows the majority of these faults are trending n s to nne ssw and parallel the direction of the gluckstadt graben faults in the salt free tornquist zone we identify two major shallow fault trends which are nw se and ne sw the majority of these faults are located above basement faults following the direction of the tornquist zone we conclude that generally basement tectonics controls activation and trends of shallow faults if salt is present the ductile salt layer causes a lateral shift between the sub and supra salt faults major plate reorganisation related to the africa iberia europe convergence and the subsequent alpine orogeny caused reactivation of pre existing faults and vertical salt movement in the late cretaceous the change of stress orientation from ne sw to a nw se during neogene caused another phase of fault and salt tectonic reactivation we explain that the ice sheet loading and or present day stress field may have acted in combination causing the recent tectonics and upward extension of the faults

axial flow hydraulic pulse testing of an argillaceous limestone lindsay limestone is an argillaceous limestone encountered in southern ontario canada the lindsay formation is regarded as a suitable geologic medium for the construction of a deep geologic repository for storing low to intermediate level nuclear waste the lindsay limestone is a nodular argillaceous rock with very low permeability requiring the use of hydraulic pulse tests for the measurement of its permeability characteristics the paper describes the triaxial testing facility the theoretical basis for the test and the procedures used to analyze the experimental results for estimating the permeability of the lindsay limestone the results are compared with the data available in the literature

microseismicity in the mid st lawrence valley charlevoix zone quebec abstract previous seismicity studies of the charlevoix zone of the mid st lawrence valley have defined the extent of the active zone continued monitoring of this zone has yielded more hypocenters that together with the previous data give a more detailed picture of the hypocentral distribution of the microactivity a more definite correlation can now be made with the known structure in this region and the faults of the st lawrence valley in general the cumulative data permit a definition of lateral boundaries of the seismic activity range of focal depths and anomalous nonseismic zones it is also possible to make a correlation with the normal faults that were probably associated with the paleorifting of the st lawrence valley but are now under compression in this seismically active region part of these preexisting partially sealed faults were most likely weakened again at the time of formation of the charlevoix impact structure

uppermantle anisotropy and the oceanic lithosphere rayleigh wave and love wave dispersion data for oceanic paths cannot be satisfied by an isotropic uppermantle and it is incorrect to invert these two datasets independently for separate isotropic structures available phase and group velocity data are inverted for oceanic structure as a function of age taking into account anelastic dispersion sphericity and anisotropy the resulting models are quite different from previous results which ignore the above effects and the extra parameters involved in proper anisotropic inversion the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age and an anisotropic low velocity zone with an age dependent anisotropy the lid or seismic lithosphere reaches a maximum thickness of 50 km which is about one half the thickness obtained in previous isotropic or pseudo isotropic inversions the seismic lithosphere therefore may be comparable in thickness to the elastic or flexural lithosphere raising the possibility that both are controlled by effects other than temperature stress and time such as mineralogy crystal orientation or partial melting the velocities in the low velocity zone are higher than inferred by previous surface wave studies

a snow sensor experiment in dronning maud land antarctica in january 2000 nine snow sensors were deployed in dronning maud land antarctica along a 355 km transect from kvitkuven near the shelf edge via the finnish research station aboa to the amundsenisen plateau the purpose was to test a sensor system for spatio temporal variations in temperature across the snow air interface and snow accumulation ablation which includes atmos pheric net balance and migrating snow dunes in the dry snow conditions environmental static electricity interfered with data transfer several sensors were disabled early while the longest record reached 6 months along the main transect the year 2000 mass balance ranged from 52 to 221 mm w e largely following spatial patterns seen by other researchers the level increased toward the edge of the ice sheet unloading of drifting snow as the slope flattens rather than increased snowfall as previously thought may be responsible for this at the hogisen ice dome site the mass balance was 897 mm w e possibly due to unloading of wind blown snow as katabatic winds are locally forced uphill this mechanism is important to maintain such topographic features along the antarctic ice sheet margin major precipitation events occurred at 3 5 week intervals and much of the precipitation fell before mid june the daily signal in temperature disappeared after the autumn equinox then the spectrum displayed a broad peak at synoptic frequencies potential temperature decreased towards the shelf edge displaying a pattern consistent with strong inversions and suggesting that strong evaporative cooling is associated with the katabatic winds

upper crustal stresses and vertical stress migration in eastern canada diversified phenomena are contributing to our knowledge of various aspects of the stress field and the origin of the crustal stresses in eastern canada both in situ stress measurements to 2100 m and earthquake fault plane solutions in the upper crust 5 20 km indicate that the maximum horizontal stress is greater than the vertical absence of earthquakes in the lower crust 20 km implies a comparatively lower deviatoric horizontal stress in this layer stress directions as determined from both in situ measurements and earthquake fault plane solutions indicate an overprint confined to the ene octant which correlates with the direction predicted by modeling of plate tectonic stresses thus spreading mid atlantic ridge stress is considered to be one of the important contributors to the stress field in eastern canada viscoelastic relaxation of this stress is considered to enhance the deviatoric stress level in the upper crust while simultaneously reducing that in the lower crust the crust acts as a stress guide within which stresses in the upper crust that are lost through brittle failure i e earthquake stress drop can be replenished from the lower crust moreover the directionality predicted by modeling of spreading mid atlantic ridge stress is maintained incomplete postglacial rebound also contributes to deviatoric compression other possible contributors to the upper crustal stress field are basal drag and membrane stress but the relative contributions from these sources are not properly understood

analysis and interpretation of borehole hydraulic tests in deep boreholes principles model development and applications a review of the literature on hydraulic testing and interpretive methods particularly in low permeability media indicates a need for a comprehensive hydraulic testing interpretive capability physical limitations on boreholes such as caving and erosion during continued drilling as well as the high costs associated with deep hole rigs and testing equipment often necessitate testing under nonideal conditions with respect to antecedent pressures and temperatures in these situations which are common in the high level nuclear waste programs throughout the world the interpretive requirements include the ability to quantitatively account for thermally induced pressure responses and borehole pressure history resulting in a time dependent pressure profile around the borehole as well as equipment compliance effects in low permeability intervals a numerical model was developed to provide the capability to handle these antecedent conditions sensitivity studies and practical applications are provided to illustrate the importance of thermal effects and antecedent pressure history it is demonstrated theoretically and with examples from the swiss nationale genossenschaft fur die lagerung radioaktiver abfalle regional hydrogeologic characterization program that pressure changes expressed as hydraulic head of the order of tens to hundreds of meters can result from 1 to 2 c temperature variations during shut in packer isolated tests in low permeability formations misinterpreted formation pressures and hydraulic conductivity can also result from inaccurate antecedent pressure history interpretation of representative formation properties and pressures requires that antecedent pressure information and test period temperature data be included as an integral part of the hydraulic test analyses

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle

does rapid change in ice loading modulate strain accumulation and release in glaciated tectonically active regions there are major glaciated regions of the world that are also seismologically active changes in the thickness of ice due to glacier surges advances or retreats produce stress changes that may be a significant fraction of the tectonic stress accumulated during an earthquake cycle the changes in ice loading can affect both the normal and shear stress on a fault with stresses being enhanced or reduced depending on glacier and fault geometry the stress change has a nearly instantaneous elastic component and a longer time scale viscoelastic component thus i propose that glacier motion can produce geodetically significant horizontal and vertical crustal displacements and can affect strain strain rate and the time of occurrence of earthquakes in regions that are not tectonically active rapid ice motion can also produce locally significant and geodetically detectable crustal deformations

some seismological and geometric features of intraplate earthquakes to understand the nature and cause of intraplate earthquakes we carried out a systematic search for common features associated with them various geological geophysical and seismic data were analyzed and geometric and seismic parameters were compared for 29 intraplate events m 4 5 occurring worldwide the results suggest that intraplate earthquakes occur by the reactivation of pre existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion two styles of faulting were observed for type a earthquakes observed in the eastern united states eastern china western europe and west africa deformation occurs by strike slip motion on steeply dipping faults type b events are usually associated with thrust or normal faulting and were observed in eastern canada fennoscandia australia and peninsular india focal depths did not explain the differences between type a and type b earthquakes rather the differences are due to the perturbation of a regional stress field by a local stress field the regional stress field for type a events is primarily due to ridge push forces the method of stress perturbation varied from region to region the earthquakes in the type b category were further divided into three subcategories type b1 occurring in eastern canada and fennoscandia type b2 occurring in australia peninsular india and central brazil and type b3 occurring in the gulf coast of the u s the inferred causes of the perturbing stresses are deglaciation intracontinental resistive forces resulting from the collision of plates and the deposition of a large thickness of sediments respectively type a events were found to be associated with intersecting faults and generally supported the intersection model of talwani 1988 and had analogs in plate boundary events

reply to comment by hampel et al on stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle reply to comment by hampel et al on stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle

recent cross formational fluid flow and mixing in the shallow michigan basin ground water with total dissolved solids tds ranging from 10 to 50 g l exists at depths between 90 and 140 m in devonian oil bearing formations in the shallow michigan basin of southwestern ontario these formations comprise mainly limestone and dolomite and the sources of the saline ground water have not been identified previously isotopic and major ion data from ground water from devonian oil bearing formations in southwestern ontario indicate that the highest salinity fluids were emplaced locally from depths of several hundred meters during the later stages of or following the wisconsinan glaciation saline water and petroleum were also emplaced into overlying pleistocene clay rich glacial deposits isostatic rebound leading to fracturing and enhanced formation permeability due to matrix expansion was probably the primary mechanism that enabled these saline fluids to migrate into discrete areas of the devonian and pleistocene formations the geochemical data presented here support a model involving cross formational fluid flow from depth occurring vertically on the scale of several hundred meters since glaciation the hydrogeologic regime in this shallow basinal system must therefore be viewed as dynamic rather than static to depths of at least 500 m over a time frame of 100 000 yr 54 refs 10more figs 2 tabs less

the eco geomorphological roles of rocky deep crevices for water supply on arid zone mountain slopes case study mehriz yazd iran rocky slope landscapes are widely distributed on arid land mountains where there are many restoration and forestation project sites this study has surveyed the role of deep crevices and stone layers for supplying water to establish trees and shrubs on arid lands rocky slopes the research was concentrated on the layers of limestone granite and andesite in central iran thirty transects each 25 m long were randomly laid out throughout the studied lithologic units correlation of vegetation cover percentage and abundance of trees were studied along with crack dimensions including width depth and length categorized into three classes large medium and low sizes along those transects the amount of ec ph organic materials caso4 caco3 soil texture n p k and soil moisture content in the cracks were also measured the results showed significant differences p 0 05 among crack properties vegetation cover and life forms in the study units also the vegetation cover and life forms have positive significant relationships with increase of crevice width as well as length and depth of each lithologic unit the findings demonstrated that the inherent potential of limestone rocky slopes with deep layers is higher than other rocky units for restoration and afforestation in this arid region

regional hydrogeology of the silurian and ordovician sedimentary rock underlying niagara falls ontario canada abstract due to concern over the potential for widespread groundwater contamination in the sedimentary rock underlying the niagara falls area this study was done to investigate the hydrogeology of the silurian and ordovician stratigraphy underlying the upper niagara river and the eastern niagara peninsula seven boreholes up to 150 m deep were drilled instrumented with multiple packer casing tested for permeability sampled for inorganic and organic solutes and monitored for hydraulic head to provide data for a conceptual model of regional groundwater flow results show that there are at least three distinct groundwater flow regimes in the bedrock the uppermost regime consists of fracture zones in the guelph and lockport formations within which hydraulic conductivity hydraulic head measurements and geochemical analyses indicate active groundwater circulation primarily discharging towards the niagara gorge and escarpment underlying the lockport formation are an overpressured high hydraulic head regime in the clinton upper cataract lower queenston formation and an underpressured low hydraulic head regime in the lower cataract upper queenston formation in both regimes geochemical analyses and permeability measurements indicate very old and saline groundwater which probably has undergone minimal migration since pre pleistocene time the implication based on the study so far is that potential groundwater contamination below the bottom of the lockport formation is probably not significant in the niagara falls area except adjacent to the niagara gorge where vertical permeability in the lower flow regimes may be enhanced

what caused the march 25 1998 antarctic plate earthquake inferences from regional stress and strain rate fields we investigate possible driving forces behind the occurrence of the 1998 antarctic plate earthquake we determine first a regional strain rate field associated with the accommodation of relative plate motion and second a vertically averaged minimum deviatoric stress field associated with lithospheric gravitational potential energy differences and deglaciation of the antarctic ice cap we find that the mechanism of this event is inconsistent with strain orientations inferred from kinematic modeling of a diffuse zone of deformation within the triple junction region stress perturbations associated with deglaciation cannot be ruled out as a triggering mechanism for this event

can deglaciation trigger earthquakes in n america a spherical self gravitating viscoelastic earth model is used to calculate the spatial and temporal evolution of the glacially induced lithospheric stress and fault stability in north america the predicted onset time of a pulse of earthquake activities the mode of failure and the magnitude of instability are investigated for three sites with different distance from the former ice margin it is found that glacial unloading is able to trigger paleo earthquakes within the ice margin near charlevoix 47 5 n 70 1 w and in wabash valley 38 5 n 87 w outside the ice margin however rebound stress decays away from the former ice margin thus glacial unloading is unlikely to have triggered the large m8 earthquakes in new madrid 36 6 n 89 5 w

the great march 25 1998 antarctic plate earthquake moment tensor and rupture history we use broadband body and mantle wave data to study the 1998 antarctic intraplate earthquake the centroid moment tensor cmt has a large non double couple component there exist two pure double couple constrained solutions that fit the data almost equally well the frequent practice of taking the best double couple gives a far from optimal solution we use p and sh body waves to determine the rupture parameters of the first and larger of the two observed subevents the best rupture plane with strike 96 dip 69 and rake 18 is compatible with only one of the two cmt solutions strike 96 dip 64 rake 23 centroid location 63 1 s 148 4 e 10 km depth centroid time 0313 02 ut and m0 1 3 1021 n m mw 8 0 the first subevent is a simple primarily westward propagating 140 km rupture of 45 s duration with average velocity 3 km s 1 it has a seismic moment of 1 2 1021 n m mw 8 0 with 75 of its moment released between 10 and 27 s and a stress drop of 240 bars the rupture is physically bounded by two fracture zones at 147 5 e and 150 e the second subevent lasted from 70 to 90 s on a fault extending from 210 to 270 km west of the epicenter with a moment of 0 3 0 6 1021 n m mw 7 6 7 8 this is a spectacular example of dynamic stress triggering over a 100 km separation distance with a time delay of 40 s the complex pattern of aftershocks is primarily controlled by preexisting fracture zones on the ocean floor

isostasy and the ambient state of stress in the oceanic lithosphere two conditions are normally considered to be characteristic of the state of stress in a system in local isostatic equilibrium the first is that the stress is hydrostatic below some depth the level of compensation and the second is that above that depth there are no vertical shear stresses in the case of a planar two dimensional mid ocean ridge these two conditions suffice to determine the stress completely except for the normal component parallel to the ridge but to determine that component an additional assumption is required it is proposed here that an appropriate additional assumption is that in unflexed regions where the stress is due only to the elevation of mid ocean ridges the deviatoric stress in the oceanic lithosphere is a minimum the unique state of deviatoric stress consistent with this assumption is horizontally compressive in a direction perpendicular to the axes of mid ocean ridges with a magnitude in old ocean basins of a few hundred bars in agreement with oceanic intraplate earthquake mechanisms at any given distance from the ridge the stress is maximum at the seafloor and it decreases with depth at about the same rate as the cooling of the lithosphere so that the entire thermal boundary layer may be regarded as acting to support the global square root of age topography of the oceans

monitoring well into abandoned deep well disposal formations at sarnia ontario a 300 m deep monitoring well was completed to the detroit river group of formations in sarnia ontario to evaluate the potential near surface impacts resulting from previous deep injection of industrial waste detailed logging testing and sampling were performed to evaluate the vertical distribution of industrial waste and to determine hydraulic conductivity and hydraulic head in the disposal horizon and in the confining formations results of hydraulic testing indicate the hydraulic conductivity of the disposal formation is 2 10 9 to 2 10 7 m s and that of most of the confining shale and limestone formations is less than 1 10 10 m s analyses of groundwater samples and results from other studies show that industrial waste characterized by elevated phenol concentrations is present in a 10 m horizon in the lucas dolomite disposal formation at 192 m depth waste is also likely present within 2 3 m thick high permeability limestone layers at 74 and 123 m depth in the confining units of the hamilt

dependence of horizontal stress magnitude on load dimension in glacial rebound models summary it has been proposed that the deglaciation of the northern hemisphere triggered large earthquakes within intraplate environments and in this paper we examine this hypothesis by evaluating quantitatively the stress state in the lithosphere produced by time dependent surface loads a series of models demonstrate the dependence of horizontal incremental stress in an elastic plate overlying an inviscid or viscoelastic mantle on the lateral extent of a load applied at the surface the horizontal stress is largest when the dominant wavelength that is twice the diameter of the load is close to eight times the elastic thickness of the plate when the mantle is inviscid and for the particular viscosity model employed in this paper close to 12 times the elastic thickness for a viscoelastic mantle at wavelengths close to the critical wavelength the horizontal incremental stress may be up to six times as large as the vertical incremental stress for appropriate earth model parameters amplification of horizontal stress is close to maximum for ice loads with a radius of 280 km comparable to the dimensions of the former ice sheet over great britain this amplification may be sufficiently large that loading by small ice sheets can lead to failure on marginally stable faults in contrast to the behaviour for large ice sheets the models also predict greater fault instability for fennoscandia than for the larger laurentide ice sheet consistent with the observation of large postglacial faults in northern sweden the model is used to predict the stability of faults and style of faulting due to rebound stresses in the absence of a background tectonic stress field since the last glacial maximum 18 000 years ago in northern europe within the formerly glaciated region thrust faulting is predicted to occur at the end of deglaciation and normal faulting is predicted to occur in peripheral regions for the entire period since the last glacial maximum

new insights into the geology of the namaqua tectonic province south africa from ion probe dating of detrital and metamorphic zircon abstract an ion microprobe study in the western part of the namaqua natal tectonic province of south africa provides new insights into ages of sedimentation magmatism and metamorphism in the bushmanland terrane concordant u pb ages and discordia regressions are reported for three samples and in combination with secondary electron microscope images th u ratios and rare earth element analyses of different zircon age domains are used to distinguish several igneous and metamorphic events detrital zircon grains from the tectono stratigraphic lowermost part of the kamiesberg subgroup louisrus formation yielded ages between 1200 and 1250 ma and formed before a first tectono thermal event at 1187 ma in contrast detrital zircon grains from a metapelitic granulite from the top of the subgroup bitterfontein formation were deposited during a previously unrecognized sedimentation stage after 1157 ma and after this first tectono thermal event therefore at least parts of the supracrustal rocks in the bus

a comparison of observed and theoretical postglacial relative sea level in atlantic canada two extreme models of late wisconsinan ice cover in atlantic canada and the northeastern u s a are shown to produce postglacial relative sea level curves that bracket existing field observations at six sites throughout the region this suggests that the true late wisconsinan ice distribution is probably intermediate to the two contrasting reconstructions proposed both ice models predict the existence of four relative sea level zones an innermost zone closest to the centre of glaciation in which relative sea level falls continuously throughout postglacial time an outermost zone in which it rises continuously and two transitional zones in which it first falls and then rises in varying proportions according to the distance from the ice margin the distinctive forms of the relative sea level curves are probably representative of each of the zones and are unlikely to be significantly perturbed even by large local ice readvances they therefore establish patterns with which future field data are expected to conform the form that the geological record of relative sea level change is likely to take within each zone is discussed and promising settings for the collection of new data are proposed the common practice of separating relative sea level into an isostatic and a eustatic component is analysed and shown to be incorrect as usually applied the practice is also shown to be unnecessary because the models discussed in this paper predict changes in relative sea level that can be compared directly with the observations

supernormal fluid pressures in sedimentary rocks of southern ontario western new york state fluid pressures up to 1 7 times greater than hydrostatic have been measured in argillaceous paleozoic rocks of low permeability in southern ontario and western new york state these supernormal formation fluid pressures were measured at depths of 50 310 m using submersible pressure transducers with straddle packers and multiple packer casings isolating the test intervals measurements were obtained over periods of 7 46 months following casing installations the pressure measurements from 11 monitoring wells are compiled and supporting hydrogeologic data for 5 selected wells are used as examples to illustrate the occurrence of supernormal fluid pressures in the ordovician silurian and devonian sedimentary sequence of southern ontario and western new york state possible explanations for the occurrence of supernormal fluid pressures in sedimentary rock are evaluated considering the available geologic and hydrogeologic information obtained from the monitoring wells based on this review it is hypothesized

induced stresses and fault potential in eastern canada due to a realistic load a preliminary analysis summary in order to understand the causal relation between postglacial rebound and earthquakes a simple disc load model is used to 1 calculate stresses induced in the lithosphere and mantle by glacial loading melting and postglacial rebound and 2 evaluate the effect of glacial loading rebound on the failure potential for earthquakes in the upper crust the dependence of the failure potential and the actual mode of failure on the coefficient of friction the ambient tectonic stress magnitude direction the stress due to the overlying rocks and lithospheric thickness are investigated prominent features of this paper are the inclusion of 1 a viscoelastic mantle and thus the migration of stress and 2 the ambient tectonic stress and overburden stress contributions in the calculation of the total stress field it is assumed that throughout the earth there are optimally oriented pre existing virtual faults that are initially close to but not at failure thus a time dependent quantity called dfsm related to the coulomb mohr failure criterion can be defined such that a negative value of dfsm would advocate faulting or earthquake activities whereas a positive value of dfsm would promote stability the results indicate that under all combinations of tectonic stress magnitude and overburden stress crustal loading promotes fault stability directly underneath the load upon the removal of the load thrust faulting is predicted within the ice margin if the horizontal stress s induced by the overburden is greater than or equal to the vertical component s of the overburden stress 121 where sjs under this condition theory predicts that faulting or earthquake activity should have reached a maximum immediately after deglaciation if the horizontal stress induced by the overburden is less than the vertical component of the overburden stress 1 l then theory predicts fault stability within the ice margin the theory predicts fault instability both north and south of the ice margin the mode of failure however is completely determined by the value of i the trade off between the tectonic stress magnitude and the overburden stress parameter 1 is also investigated it is shown that a larger tectonic stress magnitude can be used to compensate a smaller value of 1 the results of this analysis show that variations in the coefficient of friction lithospheric thickness and a ductile zone below the upper crust do not significantly affect the above conclusions

will earthquake activity in eastern canada increase in the next few thousand years knowledge of whether earthquake activity will increase in the next few thousand years is important for the planning of nuclear waste repositories assuming that fault instability portends earthquak

hydrocarbon generation as a mechanism for overpressuring in rocky mountain region overpressured reservoirs are present in the deeper parts of most basins in the rocky mountain region a variety of conditions can cause overpressuring however most high pressures in the region are caused by present day or recently active oil and gas generation or generation in the last few million years in low permeability rock successions that still contain organic matter capable of yielding thermally generated hydrocarbons rocks with above normal pressure range from devonian to tertiary and commonly are associated with low permeability tight reservoirs most of the overpressuring occurs in cretaceous and tertiary rocks overpressuring in rocks older than cretaceous is rare and where present only occurs in strata with very rich hydrocarbon source beds such as the d vonian mississippian bakken formation most organically lean pre cretaceous source beds are no longer capable of yielding enough hydrocarbons to maintain abnormal pressure nearly all overpressured reservoirs and source rocks have temperatures of approximately 200 f 93 c or higher in addition available data indicate that hydrocarbon related overpressuring does not generally occur if vitrinite reflectance ro values are less than 0 6 in oil prone strata or less than 0 7 in gas prone strata overpressured gas bearing strata generally have ro values of 0 8 or higher maximum reservoir pressures are about equal to the fracture gradient pressure in the reservoir rocks some vertical fractures in reservoir rocks are probably caused by rapid expulsion of hydrocarbons from the source beds high pressures in the rocky mountain region means that the rock succession is gas or oil saturated and discrete hydrocarbon water contacts are generally not present classical concepts of hydrodynamics do not appear to be applicable to these overpressured successions the optimum depths for exploration are generally the upper 1 000 2 000 ft 305 610 m of the overpressured succession

uranium in groundwater of the al batin alluvial fan aquifer south iraq this study focuses on identifying concentrations species spatial distribution and potential sources of uranium u in groundwater in al batin area south of iraq although few studies reported elevated concentration of u in groundwater in some parts of the al batin alluvial fan a comprehensive investigation of u in the groundwater of the entire fan is still missing so far to achieve this goal 43 groundwater samples are collected for major cations and anions trace elements total organic carbon and total inorganic carbon analyses u concentrations range between 0 1 and 98 g l with an arithmetic average of 16 g l the spatial distribution of u in groundwater shows an increase eastward and northeastward with some anomalies uo2 co3 22 uo2 co3 34 and uo2 hpo4 22 are the dominant u species according to phreeqc simulations spearman correlation analysis n 43 p 0 01 shows a positive correlation between u and k hco3 ca mg al si and rare earth elements ree well depth on the other hand had a negative correlation r 0 65 at p 0 01 with u indicating that u is dominant in more shallow groundwater this study assumes a geogenic source of u from the arabian shield in saudi arabia derived by flood plain and trapped in the east and northeast of the study area under reduced conditions of the neighbor marshes the release of uranium into the groundwater can be explained by three hypotheses the first hypothesis is desorption of u sorbed onto ferric minerals e g hematite magnetite and goethite the second hypothesis is desorption of u from clay minerals in mudstone lenses within the aquifer the third hypothesis is the release of u from the carbonate lattice structure due to the replacement with ca the relatively high eh and the elevated concentrations of so42 ca2 and na in groundwater are appropriate conditions to release u load of the supposed sources into groundwater

an updated global earthquake catalogue for stable continental regions reassessing the correlation with ancient rifts summary we present an updated global earthquake catalogue for stable continental regions scrs i e intraplate earthquakes that is available on the internet our database contains information on location magnitude seismic moment and focal mechanisms for over 1300 m moment magnitude 4 5 historic and instrumentally recorded crustal events using this updated earthquake database in combination with a recently published global catalogue of rifts we assess the correlation of intraplate seismicity with ancient rifts on a global scale each tectonic event is put into one of five categories based on location i interior rifts taphrogens ii rifted continental margins iii non rifted crust iv possible interior rifts and v possible rifted margins we find that approximately 27 per cent of all events are classified as interior rifts i 25 per cent are rifted continental margins ii 36 per cent are within non rifted crust iii and 12 per cent iv and v remain uncertain thus over half 52 per cent of all events are associated with rifted crust although within the continental interiors i e away from continental margins non rifted crust has experienced more earthquakes than interior rifts no major change in distribution is found if only large m 6 0 earthquakes are considered the largest events m 7 0 however have occurred predominantly within rifts 50 per cent and continental margins 43 per cent intraplate seismicity is not distributed evenly instead several zones of concentrated seismicity seem to exist this is especially true for interior rifts taphrogens where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category of the four rifts taphrogens that have experienced the largest earthquakes seismicity within the kutch rift india and the east china rift system may be controlled by diffuse plate boundary deformation more than by the presence of the ancient rifts themselves the st lawrence depression canada besides being an ancient rift is also the site of a major collisional suture thus only at the reelfoot rift new madrid seismic zone nmsz usa is the presence of features associated with rifting itself the sole candidate for causing seismicity our results suggest that on a global scale the correlation of seismicity within scrs and ancient rifts has been overestimated in the past because the majority of models used to explain intraplate seismicity have focused on seismicity within rifts we conclude that a shift in attention more towards non rifted as well as rifted crust is in order

metal enrichment in the groundwater of the arid environment in south africa this paper presents the enrichment tendency and spatial distribution of metals in the groundwater which is pumped out from the granitic aquifers in south africa groundwater is the sole source of water supply for the local community in the study area namaqualand and hence it was necessary to understand the controlling geochemical processes and interrelationship of metals in the groundwater the geochemical association of metals has been assessed based on the geostatistical methods the results show that geochemical processes such as oxidation leaching and evaporation besides water rock interaction are very important in controlling metal enrichment in the groundwater from highly mineralized rocks the metal enrichment index for selected toxic metals in groundwater increases in the order of cd u cr pb the observed enrichment trend could be considered as a result of mineralization of basement rocks which is facilitated by active geochemical process in the arid environment the lack of aquifer flushing due to negligible recharge helps the metals to concentrate at shallow groundwater zones supported by severe evaporation process

possible effects of erosional changes of the topographic relief on pore pressures at depth formation fluid pressures are said to be anomalous or abnormal if they differ from hydrostatic for the depth considered explanations of the origin and maintenance of anomalies seldom include the possibility of delayed adjustment of subsurface pore pressures to erosional modifications of the topographic relief yet the present paper shows that it is entirely possible for subaerial erosion to generate pore pressure changes at great depths by cross formational energy transfer in realistic field conditions conversely pressures may survive changes in the topography and be in a transient state for hundreds to millions of years thus appearing anomalous at the time of observation according to calculations for the red earth region in alberta canada present pore pressures in the devonian immediately above the precambrian basement at a depth of approximately 1400 meters may have been induced originally by erosionally shaped topography during pliocene times 12 to 1 m y b p but be adjusting now to new boundary conditions created by the erosional exposure of the sub cretaceous unconformity a 12 adjustment may already have taken place during the last 300 thousand years leaving nearly 90 of pliocene age pressures to survive to date as slowly decaying transient pressure relicts of the geologic past in view of the possible erosional effects on pore pressures demonstrated in this paper the question of anachronous formation pressures may deserve consideration in problems related to deep basin hydrology including regional groundwater resource development migration and accumulation of hydrocarbons radioactive waste isolation dating of various geologic events and so on

mineral virginia earthquake illustrates seismicity of a passive aggressive margin 1 the august 2011 m 5 8 mineral virginia earthquake that shook much of the northeastern u s dramatically demonstrated that passive continental margins sometimes have large earthquakes we illustrate some general aspects of such earthquakes and outline some of the many unresolved questions about them they occur both offshore and onshore reaching magnitude 7 and are thought to reflect reactivation of favorably oriented generally margin parallel faults created during one or more wilson cycles by the modern stress field they pose both tsunami and shaking hazards however their specific geologic setting and causes are unclear because large magnitude events occur infrequently microseismicity is not well recorded and there is little if any surface expression of repeated ruptures thus presently active seismic zones may be areas associated with higher seismicity over the long term the present loci of activity that migrates or aftershock zones of large prehistoric earthquakes the stresses causing the earthquakes may result from platewide driving forces glacial isostatic adjustment localized margin stresses and or dynamic topography the resulting uncertainties make developing cost effective mitigation strategies a major challenge progress on these issues requires integrating seismic geodetic and geological techniques

to what extent is the present seismicity of norway driven by post glacial rebound abstract the seismicity of scandinavia is low to intermediate in intensity and with magnitudes that rarely exceed 5 5 even so the seismicity is characterized by a great diversity in space and time related to the fact that its driving forces or sources of stress are multiple and also diverse in nature the dominant driving forces range from plate related such as ridge push through regional to local ones such as topography all however are somehow related to lateral inhomogeneities in lithospheric structure whereas it was earlier assumed that the post glacial uplift was the main cause for the seismicity of scandinavia we now conclude that the uplift may at most be playing a minor role along the coastal stretch of northern norway there are still some indications that the seismicity which is often shallow normal faulting and swarm related may be related to the still remaining glacial isostatic adjustment the flexuring that is needed to explain such behaviour could however also be related to erosion and sedimentation processes it will take more work to separate these potential driving forces

moment tensors state of stress and their relation to post glacial rebound in northeastern canada summary in the stable craton of northeastern canada moderate seismicity as well as glacial isostatic adjustment gia has been observed we investigate five earthquakes with moment magnitudes between 3 6 and 4 1 that have occurred in northern hudson bay since 2007 which may be triggered by gia focal mechanisms of the earthquakes are determined using a waveform fitting procedure for surface waves in which the best double couple mechanism is obtained through a grid search over strike dip and rake all events exhibit a thrust fault mechanism in general agreement with mechanisms of previously analysed earthquakes in that area stress inversion results incorporating our new mechanisms as well as previously published results exhibit significant differences from previously calculated stresses from gia models for the first time maximum horizontal stress direction shmax is compared to the modelled stress values for northeastern canada we find that the maximum horizontal stress direction strikes roughly nnw sse in contrast to previously inferred ne sw orientation of shmax our results indicate that the local stress field in northern hudson bay deviates from regional stresses resulting from the existence of a roughly e w oriented zone of faulting which is not included in existing gia models

triassic to recent tectonic evolution of a crestal collapse graben above a salt cored anticline in the gluckstadt graben north german basin abstract in this study we investigate faulting above a salt wall in the gluckstadt graben north german basin two supra salt faults are mapped from coast to coast over a distance of 6 9 km based on offshore and onshore seismic data these faults form a ca 2 km wide crestal collapse graben and pierce the seafloor salt wall evolution started in the early late triassic to early jurassic due to regional extension and resulting sub salt faulting the salt wall was eroded following exposure to costal and sub aerial erosion by the regional mid late jurassic to early cretaceous uplift late cretaceous to early paleogene compressional tectonics reactivated the vertical salt movement and shortened the salt wall creating a salt cored anticline with the crestal collapse graben above the supra salt faults were reactivated between the late eocene and middle miocene when the principal horizontal stress orientation changed from a ne sw to a nw se the present day orientation stratigraphic data indicate that these faults moved mainly in the cenozoic several observations strongly suggest that the faults continued developing during the pleistocene until today i the pleistocene unconformity is concave upwards and cut by faults ii growth strata within the marine holocene deposits above the graben imply recent tectonic movements iii onshore high resolution p wave vibroseis data of the south eastern eckernforde bay suggest about 10 m of faulted holocene strata and iv marine seismic data show the faults piercing the seafloor we suggest that the recent salt tectonics and upward propagation of supra salt faults resulted from differential ice sheet loading that effect on the salt wall stopped once ice grew over the whole structure at which time the wall subsided because of ice loading the salt wall and faults were reactivated again once the ice front retreated so that the ice loaded only one side of the structure

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

groundwater flow and radioactivity in namaqualand south africa the namaqualand area is located in the northern cape province of south africa which is characterised by arid climate where groundwater is the only source of water supply for local communities extensive groundwater sampling was carried out in the area and the physico chemical parameters inorganic constituents stable isotopes and trace metals were measured the hydrochemistry of the area indicates dissimilar groundwater composition due to complex geochemical processes where groundwater flow takes place from catchment f30a to the catchment d82b and the chemistry is controlled primarily by redox reaction dissolution and mixing processes the br cl ratio revealed that the salinity in the area is derived from seawater mixing halite dissolution and atmospheric deposition sea aerosol spray under excessive evaporative condition due to climatic aridity groundwater salinity shows increasing trend isotope results show the presence of shallow weathered zone and deep fracture controlled circulating groundwater in the crystalline basement aquifer of the area in comparison to the south african water quality standard the results obtained for gross alpha activity which could be derived from uranium isotopes show that 41 of the reported data in the area fall above the drinking water limit

the interaction of katabatic winds and the formation of blue ice areas in east antarctica blue ice areas bias are an extreme example of a local mass balance gradient and are furthermore reasonably stable in time and space owing to local feed back mechanisms a meteorological experiment performed in and around a blue ice area in dronning maud land east antarctica showed that during driftingsnow conditions surface wind speed over the blue ice behind the mountain barrier is equal to that away from the mountains when corrected for surface roughness and stability this implies that use of diagnostic katabatic wind models to estimate divergence of drifting snow can be extended to the situation where nunataks are involved in preventing the drifting snow from passing which is the case for most bias a diagnostic model is tested for a two dimensional profile in terre adelie after which it is applied to entire east antarctica the present order of magnitude estimate shows that areas sensitive to blue ice formation appear where precipitation is low and mean annual wind speed is high i e in dronning maud land and the drainage basin of lambert glacier the results appeared to be especially sensitive to a change in inversion strength a decrease in inversion strength weakens the katabatic flow and thus the amount of snowdrift transport reducing the area where bias can develop

soft sediment deformation at the base of the neoproterozoic puga cap carbonate southwestern amazon craton brazil confirmation of rapid icehouse to greenhouse transition in snowball earth stratigraphic and isotopic data identify the lower 45 m of the araras group on the southwest margin of the amazon craton as a neoproterozoic platform cap carbonate deposited below wave base upon varanger glacial diamictites of the puga formation the basal beds consist of moderately deep water pinkish dolomudstone with stratiform to wavy fenestral microbialites locally cut by tube like structures and fenestral nonmicrobial planar laminites with tepee like features above the basal carbonates are deep water bituminous lime mudstones with alternating thin calcite crusts and lime mudstone laminae commonly disrupted by calcite crystal fans pseudomorphs after aragonite the basal contact of the puga cap exhibits soft sediment deformational structures principally load casts that are here attributed to rebound induced seismicity acting upon both recently deposited carbonate sediments and underlying unconsolidated diamictite these features constitute the first clearly recognized sedimentological evidence for the rapid change from icehouse to greenhouse conditions as postulated in the snowball earth model of neoproterozoic glaciation

fault geometry and earthquakes in continental interiors abstract although large earthquakes in continental interiors are much less frequent than those along plate boundaries they have been responsible for a disproportionate amount of destruction i present a testable model for strain accumulation and seismicity in the upper crust of continental interiors intersecting faults provide a focus for strain build up resulting in local pockets of high strain accumulation rigid plates typically deform at strain rates 10 10 to 10 9 strain yr 1 but at intersecting fault zones strain accumulates at anomalously high rates of 10 8 to 10 7 strain yr 1 i e the strain rates are comparable with those at plate boundaries the resulting large earthquakes are associated with relatively short return times hundreds of years typically one of the intersecting faults appears to split and to offset the other main fault defined as a fault on which the larger offset occurs forming two parallel strands separated by a jog i also observe a rotation of one leg of the main fault with respect to the other the region of intersection is usually associated with intense fracturing increased microseismicity and uplift

generation accumulation and resource potential of biogenic gas biogenic gas is generated at low temperatures by decomposition of organic matter by anaerobic microorganisms more than 20 of the world s discovered gas reserves are of biogenic origin a higher percentage of gases of predominantly biogenic origin will be discovered in the future biogenic gas is an important target for exploration because it occurs in geologically predictable circumstances and in areally widespread large quantities at shallow depths in rapidly accumulating marine sediments a succession of microbial ecosystems leads to the generation of biogenic gas after oxygen is consumed by aerobic respiration sulfate reduction becomes the dominant form of respiration methane generation and accumulation become dominant only after sulfate in sediment pore water is depleted the most important mechanism of methane generation in marine sediments is the reduction of co2 by hydrogen electrons produced by the anaerobic oxidation of organic matter co2 is the product of either metabolic decarboxylation or chemical decarboxylation at slightly higher temperatures the factors that control the level of methane production after sediment burial are anoxic environment sulfate deficient environment low temperatu e availability of organic matter and sufficient space the timing of these factors is such that most biogenic gas is generated prior to burial depths of 1 000 m in marine sediments most of the biogenic gas formed can be retained in solution in the interstitial pore waters because of higher methane solubility at the higher hydrostatic pressures due to the weight of the overlying water column under certain conditions of high pressures and or low temperatures biogenic methane combines with water to form gas hydrates biogenic gas usually can be distinguished from thermogenic gas by chemical and isotopic analyses the hydrocarbon fraction of biogenic gas consists predominantly of methane the presence of as much as 2 of heavier hydrocarbons can be attributed to admixture of minor thermogenic gas due to low temperature degradation of organic matter the amounts of hydrocarbon components other than methane generally are proportional to temperature age and organic matter content of the sediments biogenic methane is enriched in the light isotope 12c dgr13c1 lighter than 55 ppt owing to kinetic isotope fractionation by methanogens the variations in isotopic composition of biogenic methane are controlled primarily by dgr13c of the original co2 substrate which reflects the net isotopic effect of both addition and removal of co2 the methane isotopic composition also can be affected by mixing of isotopically heavier thermogenic gas the possible complicating factors require that geologic chemical and isotopic evidence be considered in attempts to interpret the origin of gas accumulations accumulations of biogenic gas have been discovered in canada germany italy japan trinidad the united states and ussr in cretaceous and younger rocks at less than 3 350 m of burial and in marine and nonmarine rocks other gas accumulations of biogenic origin have undoubtedly been discovered however data that permit their recognition are not available

chemical osmosis reverse chemical osmosis and the origin of subsurface brines abstract calculations using recently tabulated values of density and osmotic coefficient for nacl h2o indicate that overpressuring is more than adequate to overcome chemical osmosis and drive reverse chemical osmosis in sedimentary sequences the best demonstrated overpressuring mechanism is the rapid deposition of fine grained sediments the dehydration of gypsum contributes to overpressuring for brief time intervals at shallow depths whereas water evolved during the protracted conversion of smectite to illite is probably a subordinate but continuing contributor to overpressuring at greater depth occurrences of overpressuring in sedimentary sections older than cretaceous indicate that post depositional mechanisms such as tectonic compression and aquathermal pressuring must also operate the latter may be of major importance in geothermal areas with adequate low permeability seals and a nontrivial contributor in areas of normal geothermal gradient because of shales that sharply decrease normal fluid flow the strongest arguments for the importance to present day brine compositions of membrane concentration of sea water solutes are 1 1 the correlation of d values of water molecules of pore fluid with those of local meteoric water 2 2 the need for major sources of mg2 and cl in apparently evaporite free basins even where dissolution of halite is a major contributor of solute reverse chemical osmosis still operates to leak relatively dilute water of the associated diagenetic chemical reactions that of mg2 with limestone to form dolomite is particularly effective in generating concentrated cl brines rich in ca2 it decreases the concentration of mg2 increases that of ca2 and decreases those of both so42 and co32 by precipitating caco3 and caso4 because of the ca2 common ion effect

stress relief buckles in the mcfarland quarry ottawa six quarry floor buckles in a west end ottawa bedrock quarry are described and a semi quantitative estimate of the stress field is inferred from them the maximum principal stress component is hori

development of abnormal and subnormal pressures in reservoirs containing bacterially generated gas burial of reservoirs containing a bacterially generated gas phase may lead to pressures that are above equal to or below hydrostatic the pressures that develop depend on the way in which the gas bearing volume is connected to or isolated from its surroundings where a noncompacting volume is totally isolated subnormal pressures will develop this approximates the situation in chalks which have high porosities but low permeabilities and often contain underpressured gas low pressures develop because the thermal pressuring of the gas with depth occurs at a lower rate than the increase in hydrostatic pressure and because the gas dissolves in the water when the gas bearing volume is freely connected to surrounding normally pressured sediments the gas pressures remai hydrostatic but the volume of gas steadily diminishes as it dissolves in the pore water if gas occupies 40 of the pore volume at 1 000 ft 305 m it will all be in solution by 4 600 ft 1 402 m and a gas phase will no longer exist water must flow in to replace the dissolving gas or the rock must compact this is the situation for normally compacting shales when the gas is in an isolated but variable volume system such as a compacting shale pressure rises above hydrostatic due to sediment loading this mechanism likely has produced many of the shallow sands charged with high pressure gas that are a drilling hazard in many offshore areas

surface winds over the antarctic continent a review surface winds over antarctica often classified as katabatic are intimately related to the orientation and steepness of the underlying ice terrain such flows result primarily from the strong radiational cooling of the sloping ice surface which creates a downslope directed horizontal pressure gradient force it is possible to diagnose the time averaged near surface streamline patterns of cold air drainage currents using recently compiled detailed antarctic ice topography maps and appropriate estimates of the strength of the surface temperature inversion the resulting streamlines agree with available observations and illustrate the high degree of nonuniformity of gravity driven flows off the ice sheets in certain interior sections negatively buoyant air from a large catchment area drains through a restricted section of coastline such confluence zones represent regions of enhanced supplies of cold air and are shown to be related to anomalously strong katabatic winds implications for sea ice formation are discussed

effect of viscosity structure on fault potential and stress orientations in eastern canada summary previous investigations of the causal relationship between postglacial rebound and earthquakes in eastern canada have focused on the mode of failure and the observed timing of the pulse of earthquake faulting activity following deglaciation in this study the observational database has been extended to include observed orientations of the contemporary stress field and the rotation of stress since deglacial times it is shown that many of these observations can be explained by a realistic ice history and a viscoelastic earth with a uniform 1021 pa s mantle the effects of viscosity structure on the above predictions are also examined it is shown that since most of the above observations are found within the ice margin they are not very sensitive to lithospheric thickness also the inclusion of a 25 or 50 km ductile layer within the lithosphere will not decouple the seismogenic upper crust high viscosity 1022 pa s in the lower mantle is rejected by the stress orientation and rotation observations a low viscosity 6 times 1020pa s upper mantle with 1 6 times 1021 pa s in the upper part of the lower mantle and 3 times 1021 pa s in the lower part of the lower mantle below 1200 km depth has been found to give predictions that are in general agreement with the observations

magnetotelluric interpretation of crustal and mantle structure in the grenville province summary accurate determinations of depths and conductivities of electrical structures in shield regions are often difficult because of the inhomogeneity of the uppermost crust a magnetotelluric mt station bat in the grenville province of the precambrian shield in eastern canada has been in operation since 1975 for time dependency studies of electrical resistivity changes related to earthquakes the mt response of the station displays low skew with small to moderate anisotropy one dimensional inversion of the apparent resistivity and phase reveals two well defined conductors in the crust one at 10 km and the second at the base of the crust the latter has a resistivity less than 50 m these results are substantiated by three additional mt stations located up to 40 km distant data from other new mt stations and from stations previously published in the literature are compared with two dimensional computer model results and with the three dimensional analogue scale model results of dosso et al while additional data for periods less than 100 s would be desirable the results from a number of the mt stations are not inconsistent with a widespread occurrence of a conducting zone at the base of the crust in the grenville the inversion analysis also indicates the existence of a conductor at some depth greater than 100 km with a resistivity less than 30 m this may coincide with a seismic low velocity zone observed in the mantle under the canadian shield

hydrogeology of sedimentary basins abstract hydrogeologic environments in sedimentary basins are as variable as are the different types of basins important hydrologic characteristics can be used to distinguish the different types of basin 1 the topographic setting as determined by the geologic and structural history of the basin 2 permeability distribution within the basin and 3 potential energy distributions and flow mechanisms these parameters control residence times of waters rates and directions of saline groundwater flow and the origin and chemical composition of the saline waters the gulf coast and palo duro basins texas exemplify two end member types of sedimentary basins the gulf coast basin is a relatively young tertiary age basin which is presently compacting fluid movement is from the overpressured undercompacted sediments up the structural dip or up fault zones into the hydrostatic section natural fluid pressures are either hydrostatic or overpressured the palo duro is an older paleozoic age basin that has been tectonically uplifted fluid flow is gravity driven from topographically high recharge areas to discharge in topographically low areas fluid pressures are subhydrostatic fluids discharge more easily than they are recharged not all flow is derived by a simple recharge discharge model brines may flow from other basins into the palo duro basin and waters may discharge from the palo duro basin into other basins areal differences in the chemical composition of the basin brines may be the result of different origins

the october 2005 georgian bay canada earthquake sequence mafic dykes and their role in the mechanical heterogeneity of precambrian crust on 20 october 2005 at 21 16 utc a moderate earthquake mn 4 3 occurred in an area of low seismicity within georgian bay approximately 12 km north of thornbury ontario 44 67 n 80 46 w despite its moderate magnitude it was exceptionally well recorded and is of particular interest because of its location 90 km from a proposed long term storage facility for low and medium level nuclear waste no damage was reported but ground shaking was felt to a distance of 100 km within 24 hours after the mainshock four portable seismograph systems were in stalled in the epicentral region in total eight events were recorded over a 4 day period including a foreshock and six aftershocks the unusually rich dataset from this moderate earthquake sequence enabled robust determination of hypocentral pa rameters including well constrained focal depths for most events for the mainshock we estimated a seismic moment of m0 4 5 10 14 n m and corner frequency of 3 7 hz based on a spectral fit using brune s source model least squares waveform inversion of p and s phases yielded a double couple focal mechanism with a reverse sense of slip and northwest striking nodal planes the reverse mechanism and mid crustal focal depths 10 12 km are characteristic in general of more abundant seismicity located 200 km northeast of this event in the western quebec seismic zone these parameters differ however from shallow 2 6 km earthquakes with predominantly strike slip mechanisms observed near lake erie 200 km to the south we attribute this north south change in rupture mechanism to variations in crustal stress induced by postglacial isostatic rebound aeromagnetic data in and around the epicentral region reveal prominent northwest striking lineations caused by precam brian mafic dykes under midcrustal conditions the dyke material is mechanically stronger than generally more felsic upper crustal host rocks we propose that where large dykes are favorably oriented with respect to the stress field they may strongly influence the locations of intraplate earthquake rupture in shield regions

modeling of the thermo hydro mechanical chemical response of sedimentary rocks to past glaciations abstract thermo hydro mechanical chemical thmc coupled processes that have resulted from long term past climate changes and glaciation cycles in the sedimentry rocks of southern ontario are investigated a conceptual numerical model has been developed to solve four coupled partial differential equations pdes which represent hydraulic thermal mechanical and chemical processes the finite element method is used to solve the pdes under transient surface boundary conditions imposed by past glaciation cycles to predict the hydraulic mechanical thermal and geochemical responses of the geological system the results show that past glaciations have a significant impact on the hydraulic gradient and pressure vertical effective stress and salinity profiles and a limited effect on the permafrost depth the predicted results show good agreement when compared with the field data for the total dissolved solid rock strength and quality the results show relatively good agreement with the anomalous pore water pressure profile in the field the modeling results indicate that the infiltration depth of glacial melted water is less than 300 m and are consistent with the field observation of total dissolved solids at the level of a deep geological repository dgr for low and intermediate level radioactive wastes being planned in these rock formations a safety factor of 6 9 is predicted against failure by using hoek brown failure envelopes while a low safety factor of 0 83 is predicted at the shallower level of the silurian salina formation it is found that solute transport at the middle and upper ordovician formations are diffusion dominated at depths of 300 m or more and controlled by diffusion advection above 300 m based on the results obtained the modeling of a past glaciation can be used with reasonable confidence in predicting the impact of future glaciations related to the long term safety and stability of the proposed dgr in the sedimentry formation however for site specific conditions thmc modeling is very sensitive to material properties and sensitivity analysis is required for future model development