far field pressurization likely caused one of the largest injection induced earthquakes by reactivating a large preexisting basement fault structure the mw 5 1 fairview oklahoma earthquake on 13 february 2016 and its associated seismicity produced the largest moment release in the central and eastern united states since the 2011 mw 5 7 prague oklahoma earthquake sequence and is one of the largest earthquakes potentially linked to wastewater injection this energetic sequence has produced five earthquakes with mw 4 4 or larger almost all of these earthquakes occur in precambrian basement on a partially unmapped 14 km long fault regional injection into the arbuckle group increased approximately sevenfold in the 36 months prior to the start of the sequence january 2015 we suggest far field pressurization from clustered high rate wells greater than 12 km from this sequence induced these earthquakes as compared to the fairview sequence seismicity is diffuse near high rate wells where pressure changes are expected to be largest this points to the critical role that preexisting faults play in the occurrence of large induced earthquakes

stochastic analysis of transport in a combined heterogeneous vadose zone groundwater flow system 1 first order analysis was used to investigate the effect of a few characteristics of the vadose zone and the solute source at the soil surface on the expected breakthrough curves btcs of tracer solutes in a combined unsaturated saturated spatially heterogeneous formation with a three dimensional statistically anisotropic structure the analysis is based on a stochastic continuum representation of the stationary and nonstationary eulerian velocity vectors in the unsaturated and saturated domains respectively and a general lagrangian description of the solute mass flux in steady state flow results of the present analysis suggest that the length scales and the flow characteristics of the spatially heterogeneous unsaturated zone that affect the travel time probability density function between the soil surface and the water table also affect the expected solute btc at a control plane located downstream in the groundwater the flow in the unsaturated zone might enhance the early arrival time and the spreading of the expected solute btc in the groundwater especially when the vertical extent of the unsaturated zone is relatively large when the unsaturated zone consists of relatively dry coarse textured stratified soil material and when the horizontal extent of the solute source in the direction of the mean groundwater flow is relatively large the effect of the characteristics of the vadose zone and the solute source at the soil surface on the expected solute btc in the groundwater decreases as the distance to the control plane increases and as the process of the solute breakthrough is more advanced the relatively good agreement between the results of the presentfirst order stochasticanalysiswiththeresultsofdetailed numericalanalysesofflow and transport in a three dimensional heterogeneous combined vadose zone groundwater flow domain suggests that the first order stochastic analyses may be sufficiently reliable to showappropriatetrendswhichmightoccurinrealisticcombinedvadosezone groundwater flow systems citation russo d and a fiori 2009 stochastic analysis of transport in a combined heterogeneous vadose zone groundwater flow system water resour res 45 w03426 doi 10 1029 2008wr007157

twin lake tracer tests transverse dispersion two natural gradient dispersion tests were performed at the chalk river nuclear laboratories in ontario in 1982 and 1983 during the field tests 131i was used to label the groundwater and its activity was measured in situ collecting continuous records of activity versus depth at selected times and of activity versus time at selected locations curves generated by a three dimensional analytical solution to the advection dispersion equation were fit to activity versus depth scans recorded at various locations in the test aquifer within the individual velocity regions the vertical dispersivities were 0 0006 and 0 0008 m with the arithmetic average 0 0007 m as calculated from the 1982 data the vertical dispersivity values calculated from 1983 data were 0 0014 and 0 0010 m for the high and intermediate velocity regions respectively with an arithmetic average 0 0012 m the increase in dispersivity was attributed to the error associated with the sampling and fitting procedures the average vertical dispersivity of the tracer test aquifer was an order of magnitude less than the average longitudinal dispersivity 0 0010 m versus 0 010 m for the intermediate velocity region within individual velocity regions the vertical dispersivity of the porous medium was independent of the travel distance of the tracer and was proportional to the velocity

characterization of aquifer heterogeneity by in situ sensing in analyzing groundwater flow and mass transport most commonly the heterogeneity of a geologic formation is quantified by the field mapping of the hydraulic conductivity distribution in this paper two alternative approaches are proposed according to the first nonparametric approach aquifer heterogeneity is characterized in terms of spatial variability in the concentration field generated in a natural gradient tracer test with a high energy gamma emitting radiotracer in situ sensing technology is used for mapping the concentration distribution and collected concentration versus depth profiles are correlated to produce the local scale geometric model of aquifer heterogeneities for further numerical groundwater flow and mass transport modeling in the second parametric approach heterogeneity is characterized in terms of spatial variability of the groundwater velocity rather than in terms of spatial variability of the hydraulic conductivity geostatistics is used to characterize the local scale velocity variation in terms of velocity integral scales in three orthogonal directions in the longitudinal along the mean flow and two transverse across the flow directions the velocity correlation volume is estimated as 16 68 2 0 22 m it defines the characteristic volume for the field scale groundwater flow and mass transport modeling it was concluded that the field mapping of aquifer structure by measuring concentrations and travel times of a radiotracer leads to a fundamentally new approach to the characterization of geologic heterogeneity and offers a reliable means for solving this complex problem of contemporary hydrogeology in quantitative terms

the use of velocity and conductivity data for the quantification of heterogeneity a comparison hydraulic conductivities of a portion of the twin lake aquifer are derived from grain size analyses performed at 3 cm vertical sampling intervals in four boreholes spaced l m apart correlation of conductivity logs between four boreholes leads to a geometrical model which corresponds closely to the spatial structure derived from the velocity field of previous tracer tests histogram and correlogram analyses of conductivities agree closely with those of velocities and the two data sets appear equally useful for characterizing the aquifer and its spatial variability using darcy s law flow velocities and conductivities are combined to calculate a theoretical hydraulic gradient comparison to gradients observed at the site reveals agreement on a large scale however differences exist in detail because observed piezometric heads fail to reflect small scale heterogeneity since these differences are significant for contaminant transport prediction it is recommended for future studies to directly measure flow velocities from a tracer experiment rather than to reply on head measurements and on darcy s law for the calculation of transport parameters

simulation of groundwater flow in a crystalline rock aquifer system in southern ghana an evaluation of the effects of increased groundwater abstraction on the aquifers using a transient groundwater flow model monitored groundwater level data well logs and aquifer data as well as the relevant surface hydrological data were used to conceptualise the hydrogeological system of the densu basin in southern ghana the objective was to numerically derive the hydraulic conductivity field for better characterization of the aquifer system and for simulating the effects of increasing groundwater abstraction on the aquifer system in the basin the hydraulic conductivity field has been generated in this study through model calibration this study finds that hydraulic conductivity ranges between a low of 2 m d in the middle sections of the basin and about 40 m d in the south clear differences in the underlying geology have been indicated in the distribution of aquifer hydraulic conductivities this is in consonance with the general assertion that the hydrogeological properties of the aquifers in the crystalline basement terrains are controlled by the degree of fracturing and or weathering of the country rock the transient model suggest aquifer specific storage values to range between 6 0 10 5 m 1 and 2 1 10 4 m 1 which are within acceptable range of values normally quoted for similar lithologies in the literature there is an apparent subtle decrease in groundwater recharge from about 13 of the annual precipitation in 2005 to about 10 3 of the precipitation in 2008 the transient model was used to simulate responses of the system to annual increment of groundwater abstraction by 20 at the 2008 recharge rates for the period 2009 2024 the results suggest that the system will not be able to sustain this level of abstraction as it would lead to a basin wide drawdown in the hydraulic head by 4 m by the end of the prediction period it further suggests a safe annual increment in groundwater abstraction by 5 under business as usual recharge conditions identification and protection of groundwater recharge areas in the basin are recommended in order to safeguard the integrity of the resource under the scenario of increased abstraction for commercial activities in the basin copyright 2012 john wiley sons ltd

equivalent vadose zone steady state flow an assessment of its capability to predict transport in a realistic combined vadose zone groundwater flow system 1 the applicability of an equivalent steady state vadose zone flow model to a realistic transient three dimensional heterogeneous combined vadose zone groundwater flow system was tested here two cases pertinent to semiarid regions and the presence or absence of an irrigated crop were analyzed and are presented in detail using the hydraulic properties from the bet dagan trench in addition the case of a more humid region characterized by additional summer precipitation and soils of different textures was analyzed and is discussed briefly results of the analyses suggested that when the water table is located at sufficiently large distance from the soil surface the vadose zone can be divided conceptually into two distinct zones a highly transient near surface zone and a deeper quasi steady state zone under these conditions an equivalent steady state influx obtained by averaging the cumulative flux of the net applied water over the relevant time period may provide a relatively good approximation of the cumulative water flux that crossed the water table as for solute transport in all cases examined the trajectories of the centroid of the solute plume and the mean and the standard deviation of the solute breakthrough curves at a given horizontal control plane cp expressed as functions of the cumulative flux crossing the pertinent horizontal cp associated with the transient flows were in relatively good agreement with their counterparts associated with the equivalent steady state flows particularly under noncropped conditions and when the soil texture is coarser the main finding of this study is that for the case in which the water table is located at sufficiently large distance from the soil surface equivalent steady state vadose zone flow may reconstruct the true solute btc or the solute travel time pdf at a horizontal cp located in the vicinity of the water table depth the latter finding applies to heterogeneous soils of different textures and to different atmospheric forcing conditions at the soil surface and in the presence or absence of vegetation and despite the fact that features of the transport unique to vadose zone transient flow induced by the temporal fluctuations in the water table depth cannot be reproduced by the equivalent steady state vadose zone flow

constraining permeabilities in a large scale groundwater system through model calibration abstract the range of field estimates of permeabilities in rocks of the atikokan research area ara canada has been reduced by calibrating a groundwater flow model of the ara the flow model was calibrated to the recharge component of the water balance and to measured freshwater heads in boreholes a good match between field and simulated recharge and between measured and simulated heads was obtained with two different permeability depth distributions that differed by up to two orders of magnitude in places solute transport simulation of the distributions of total dissolved solids tds chlorides cl and oxygen 18 18 o in groundwater in the area was performed to further refine the permeability estimates vertical average linear groundwater velocities from the calibrated flow model were used in one dimensional solute transport models of the system to generate depth concentration profiles of tds cl and 18 o recharge midline and discharge area models of both the fracture zones and the rock mass were employed the midline area is the narrow zone that separates the recharge downward flow area from the discharge upward flow area groundwater flow is essentially horizontal in the midline area envelopes formed by the simulated profiles that were created with the velocities of one simulation case more tightly enclosed the field data tds cl 18 o than those of another simulation case indicating that velocities of the former simulation case better represent the hydrodynamics of the real system the models demonstrate that the scatter of tds cl and 18 o field data for the ara is consistent with the groundwater flow model predictions and can be explained by the complexity arising from different hydraulic regimes recharge midline discharge and hydrogeologic environments fracture zones rock mass of the regional flow system solute transport simulation of hydrochemical constituents can aid in refining and constraining permeabilities in large scale groundwater systems

the 2016 mw5 1 fairview oklahoma earthquakes evidence for long range poroelastic triggering at 40 km from fluid disposal wells abstract wastewater disposal in the central u s is likely responsible for an unprecedented surge in earthquake activity much of this activity is thought to be driven by induced pore pressure changes and slip on pre stressed faults which requires a hydraulic connection between faults and injection wells however direct pressure effects and hydraulic connectivity are questionable for earthquakes located at large distances and depths from the injectors here we examine triggering mechanisms of induced earthquakes which occurred at more than 40 km from wastewater disposal wells in the greater fairview region northwest oklahoma employing numerical and semi analytical poroelastic models the region exhibited few earthquakes before 2013 when background seismicity started to accelerate rapidly culminating in the mw5 1 fairview earthquake in february 2016 injection rates in the 2 2 5 km deep arbuckle formation started to increase rapidly in 2012 about two years before the start of seismicity increase most of the injection activity was concentrated toward the northeast of the study region generating a relatively cohesive zone of pressure perturbations between 0 1 and 1 mpa much of the near injection seismicity was likely triggered by pressure effects and fault assisted pressure diffusion to seismogenic depth outside of the high pressure zone we observed two remarkably detached linear seismicity clusters which occurred at 20 to 50 km distance from the initial seismicity and 10 to 40 km from the nearest high rate injector semi analytical models reveal that poroelastically induced coulomb stress changes surpass pore pressure changes at these distances providing a plausible triggering mechanism in the far field of injection wells these results indicate that both pore pressures and poroelastic stresses can play a significant role in triggering deep and distant earthquakes by fluid injection and should be considered for seismic hazard assessment beyond the targeted reservoir

earthquake potential of the sichuan yunnan region western china abstract we estimate the seismic hazard potential in the sichuan yunnan region western china using three different approaches our first approach based on the assumption that the earthquake probability is proportional to the past seismicity rate uses a regional earthquake catalog to constrain the probability model a retrospective test shows that the forecasts have some predictive power for strong events occurred on fault segments with shorter earthquake recurrence time but not for that with longer recurrence time such as the longmenshan fault our second approach based on the assumption that the earthquake probability is proportional to crustal strain rate uses secular geodetic strain rate deduced from gps velocity data to constrain the probability model a retrospective test of the model with earthquake occurrence of the past 30 years shows that the model forecasted poorly however the model seems to forecast spatial intensity of earthquakes for the past 500 years reasonably well suggesting that the geodetic strain rate obtained at the decadal scale may still be a good indicator of long term earthquake activity in the region but only at a time scale of hundreds of years our third approach uses gps velocity data to determine the seismic moment accumulation rates on major faults and a historical earthquake catalog to estimate seismic moments released in the past comparison of the two yields estimates of present day seismic moments cumulated on major faults and a retrospective test shows some predictive power of the method our result suggests that numerous faults in the sichuan yunnan region have cumulated seismic moments capable of producing m 7 5 earthquakes including the xiaojiang jiali northern nujiang nandinghe and red river puer faults and the junction fault between the xianshuihe and ganzi yushu faults

numerical simulations of twin lake natural gradient tracer tests a comparison of methods the primary objectives of the twin lake experiments have been to study geologic heterogeneities and field scale dispersion and to provide data for developing and evaluating groundwater flow and transport models the experiment reported here was undertaken in 1987 1988 to expand the studies of heterogeneity and dispersion from a 40 m scale investigated in 1983 to a full 270 m scale from the point of tracer injection to the groundwater discharge zone the hydrogeologic setting the experimental and analytical methods and the interpretation of experimental data are the topics of discussion in this paper the 1983 and 1987 1988 tracer tests were used to evaluate the predictive abilities of various numerical groundwater flow and transport models the modeling is done along the mean flow direction in the vertical plane the two dimensional finite element modeling was successful in simulating the hydraulic head distribution but not the groundwater motion or the tracer transport in addition owing to the advection dominated nature of the groundwater flow the transport simulation suffered from numerical dispersion significant improvements in simulations were obtained using method of characteristics and random walk based computer models the influence of dimensionality on the transport simulation was evaluated by comparing the two and three dimensional random walk simulations it was found that over the first 40 m along the mean flow path the three dimensional simulation does not reproduce the plume migration any better than the two dimensional simulation does random walk simulations of the transport observed in the 1983 and 1987 1988 tests are also done on the basis of the advection dispersion equation and tracer test derived velocities without invoking the concept of hydraulic conductivity and darcy s law these simulations were found to be superior to simulations based on the coupled flow and transport models it was also found that the simulated hydraulic head distribution is insensitive to spatial variations in hydraulic conductivity and the simulated groundwater velocity distribution is inappropriate for transport modeling it was concluded that the advection dispersion models of the local scale transport perform better in predicting the tracer migration at the twin lake aquifer using measured velocities rather than velocities simulated by a flow model

twin lake tracer tests setting methodology and hydraulic conductivity distribution following evaluation of three potential sites a fluvial sand aquifer with high 0 7 1 6 m d 1 linear average groundwater flow velocities was instrumented with a fully penetrating injection well and 82 monitoring installations over a 40 m flow path length two natural gradient tracer migration experiments have employed pulse injections of a nonreactive radioisotope 131i in a study of hydraulic conductivity structure and dispersive characteristics of the flow system the use of a gamma emitting radionuclide in these experiments allowed measurement of tracer distribution by scanning fully penetrating boreholes with a scintillation detector this technique provided many advantages in data collection over conventional tracers including unprecedented resolution of the vertical distribution of tracer measurements without pumping and the attendant concerns for flow system perturbation and minimal manpower for sample analysis tracer breakthroughs at monitors along the axis of flow revealed the presence of heterogeneities in aquifer hydraulic conductivity at two scales over the 40 m path length six regions with hydraulic conductivities substantially different from adjacent strata were identified thicknesses of these regions varied from 0 2 to more than 3 m their lateral extents in the direction of groundwater flow ranged from 15 m to more than 40 m smaller strata with an average thickness of 0 34 m and lengths of less than 10 m were detected within all six of the hydraulic conductivity regions but there was no evidence of increases in local dispersivity with increased transport distance as a result of these variations the six hydraulic conductivity regions do however have measurable effects on whole aquifer dispersion stratification characteristics of the tested aquifer believed to have been deposited in a sandy braided river are consistent with those observed in similar modern environments estimation of the magnitude and spatial structure of hydraulic conductivity variations in aquifers of concern would be greatly aided by studies of the stratification characteristics in well exposed modern or lithified sedimentary analogues

high rate injection is associated with the increase in u s mid continent seismicity an unprecedented increase in earthquakes in the u s mid continent began in 2009 many of these earthquakes have been documented as induced by wastewater injection we examine the relationship between wastewater injection and u s mid continent seismicity using a newly assembled injection well database for the central and eastern united states we find that the entire increase in earthquake rate is associated with fluid injection wells high rate injection wells 300 000 barrels per month are much more likely to be associated with earthquakes than lower rate wells at the scale of our study a well s cumulative injected volume monthly wellhead pressure depth and proximity to crystalline basement do not strongly correlate with earthquake association managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes

groundwater flow modeling and particle tracking for chemical transport in the southern voltaian aquifers groundwater is the major source of water supply for most uses in the rural settlements in ghana a groundwater flow model was calibrated for some aquifers of the southern voltaian sedimentary system under steady state conditions the objective was to determine estimates of the hydraulic conductivities of the different hydrostratigraphic units of the southern voltaian and the distribution of recharge from precipitation data on the stable isotopes of oxygen and hydrogen from the study area suggest that groundwater recharge in the area is from rainfall the calibrated steady state model suggests that aquifer hydraulic conductivities in the study area range from 1 19 to 6 3 m day hydrostratigraphic unit specific hydraulic conductivities are discussed the calibrated recharge ranges from 3 81e 05 m day to 6 0e 04 m day which represents 0 9 6 of the precipitation in the form of rainfall six distinct flowpaths have been defined using particle tracking the particle tracking simulation suggests travel times in the range of 380 to 5 199 years from recharge areas to discharge areas along the flowpaths identified a contaminant dropped at the recharge areas in the central sections of the model area would travel at these rates along the flowpaths assuming that advection is the dominant transport process inverse geochemical modeling indicates the dissolution of albite k feldspars and anorthite respectively along flowpaths i and iv the inverse modeling along flowpaths i and iv suggest the dissolution of albite k feldspar and anorthite respectively at 1 085e 06 3 16e 08 and 3 168e 07 mmol year

the impeller meter for measuring aquifer permeability variations evaluation and comparison with other tests a knowledge of the variation of horizontal hydraulic conductivity with vertical position k z is important in understanding the transport and dispersive properties of aquifers using an impeller meter to measure the discharge distribution in a screened well while pumping at a constant rate is a promising technique for obtaining the k z function such an application is described herein and the resulting k z functions are compared with those obtained previously using tracer tests and multilevel slug tests impeller meter data were the most convenient to obtain and tracer data the most difficult the k z functions obtained by the three methods were not identical but quite similar overall this similarity between both borehole tests and the larger scale tracer test showed that nonstationary hydraulic conductivity trends in a stochastic hydrologic sense exist in the test aquifer the impeller meter method was better able to detect the higher k layers than was the multilevel slug approach overall the results suggest that a practical strategy for fitting impeller meter tracer or multilevel slug test data to a given aquifer is to use the selected testing procedure to obtain a dimensionless distribution and then a standard pumping test to measure combining both types of information enables dimensional values for k z to be calculated in low permeability aquifers or near the bottom of a test well the fluid velocity due to pumping may be below the stall velocity of an impeller thus there is a definite need for the commercial development of more sensitive flow measuring devices such as heat pulse flowmeters hess 1986 which will extend the resolution of this field method

the spatial footprint of injection wells in a global compilation of induced earthquake sequences fluid injection can cause extensive earthquake activity sometimes at unexpectedly large distances appropriately mitigating associated seismic hazards requires a better understanding of the zone of influence of injection we analyze spatial seismicity decay in a global dataset of 18 induced cases with clear association between isolated wells and earthquakes we distinguish two populations the first is characterized by near well seismicity density plateaus and abrupt decay dominated by square root space time migration and pressure diffusion injection at these sites occurs within the crystalline basement the second population exhibits larger spatial footprints and magnitudes as well as a power law like steady spatial decay over more than 10 kilometers potentially caused by poroelastic effects far reaching spatial effects during injection may increase event magnitudes and seismic hazard beyond expectations based on purely pressure driven seismicity

earthquake potential in and around china estimated from past earthquakes 1 we present an earthquake potential estimate for magnitude 5 4 or larger earthquakes for china the potential is expressed as the rate density or the probability per unit area magnitude and time and it is based on smoothed seismicity we constructed a special earthquake catalog which combines previous catalogs covering different times after deriving regression relationships we estimated moment magnitudes for some events then we used the special catalog for constructing our smoothed seismicity model and testing it retrospectively using maximum likelihood we estimated the completeness threshold the b value and the corner magnitude we adopted a kind of gutenberg richter distribution with modifications at higher magnitude and assumed a uniform b value and upper magnitude limit derived from the special catalog from smoothed seismicity we estimated local a values we have begun a prospective test finding that earthquakes since the beginning of 2000 are quite compatible with the model

southern california deformation southern california is one of the most seismically active places in the united states and has therefore been of long standing interest to geoscientists in their perspective jackson et al discuss recent work to collect geodetic data on the motion and earthquake potential of the faults in southern california