experiments on surface deformation arising from a subsurface fracture laboratory model simulation of large scale earth processes is rarely undertaken because of scale effects nonlinearity and questions of representativeness with respect to the real case hydraulic

frequency and magnitude biases in the fryberger model with implications for characterizing geomorphically effective winds abstract the fryberger model uses standardized wind data to estimate regional aeolian sediment drift potential dp which allows for interpretation and classification of aeolian dune landscapes this paper identifies systematic frequency and magnitude biases in the model that result from i variations in wind direction sector range which affects frequency bin size for determining percent occurrence of transporting winds and ii use of wind speed class mid point values over more statistically representative values e g mean median or minimally classified whole knot wind speeds in the magnitude weighting factor for dp calculations the significance of these biases is tested using unclassified data from stanhope prince edward island canada frequency bias resulting from wind data aggregation into direction sectors of varying size produces statistically significant discrepancies in dp and rdp estimates for this dataset when 36 point 10 s of degree data are reduced to 16 sectors cardinal directions receive one extra direction class and the magnitude of dp and rdp values decreases by 1 4 and 2 8 respectively compared to 16 equal 22 5 sectors derived from original data this results from under representation of intermediate direction classes for this dataset the effects on rdd less than 1 and directional variability ratio rdp dp are insignificant magnitude biases result from the use of the wind speed class mid point values instead of other statistically representative measures of wind speed in dp calculations in that wind speed distributions are often positively skewed mid point values yield an over estimate of total dp by as much as 34 and rdp by up to 22 for this dataset over those derived using mean median and whole knot minimally classified values this difference is statistically significantly at both the individual wind speed direction category level and at the aggregate directionally summed level and causes rdp vectors to shift 3 5 to the south though the impacts of these frequency magnitude biases are site specific and modest the effects on rdp estimation may be more significant in complex i e multi modal wind regimes and or in environments with more frequent high magnitude winds from the cardinal directions given the increased availability of more precise unclassified wind data most of these systematic frequency magnitude biases can be avoided recommendations on reducing inaccuracies imposed by these biases include i using to the degree wind data where available and categorizing into 16 equal 22 5 direction sectors ii using either wind speed class statistical mean values or minimally classified whole knot values in dp calculations and iii recognizing that converting 36 point 10 s of degrees data to 16 direction classes may introduce a frequency bias toward the cardinal directions and will cause inaccuracies in dp and rdp estimates of an amount that depends on the wind regime further research is needed to assess the implications of such biases in different wind regimes and into the influence of localized supply and transport limiting factors on regional scale assessments of dune morphodynamics and mobility these findings are also relevant for other applications that use categorized wind speed direction data such as dust or contaminant plume dispersion modelling

interseismic stress accumulation at the locked zone of nankai trough seismogenic fault off kii peninsula abstract a primary source of stress variation prior to great subduction zone earthquakes is the tectonic loading due to plate convergence we have calculated the elastic stress around the locked zone accumulated during an interseismic period numerically using a 2d plane strain finite element model in the nankai trough off kii peninsula and examined its dependence on elastic properties and some boundary conditions for the modeling we used the geometry of subducting plate interface determined previously through seismic surveys and the physical properties that were obtained through iodp scientific drilling offshore kii peninsula to construct a physically realistic model a dislocation along the plate interface is calculated from a 5 m displacement imposed on one side of the subducting plate with the locked zone defined at a depth of 10 to 25 km along the plate interface calculated shear stress is maximized at the downdip edge of the locked zone decreases exponentially seaward and is almost zero near the updip edge maximum shear stress is primarily proportional to the young s modulus of the overlying section comparing the maximum shear stress with the average stress drop for subduction earthquakes 3 4 mpa the most appropriate young s modulus and poisson s ratio ranges are 50 70 gpa and 0 3 respectively which are in good agreement with previous estimations from observed vp vs the stress accumulated during one seismic cycle can be reasonably explained by a linear elastic model with an appropriately sized locked region we found that the envelope of simulated horizontal displacement on the surface agrees well with gps velocity data which also supports this inference disturbance near the updip edge is no larger than 0 1 mpa of stress or 0 1 radian of tilt which are difficult to detect with current borehole measurement techniques and likely complex borehole conditions

longevity of aeolian megaripples abstract megaripples are distinguished from regular ripples by their larger dimensions and bimodal grain size distributions the interplay between wind grain size and ripple morphology height and wavelength controls their development two main mechanisms limit megaripple height the first megaripple flattening due to winds that are above the fluid threshold of the coarse grains destroys the armoring layer of the megaripple the second is megaripple erosion by the impacts of fast moving fine saltating grains that propel the coarse grains constituting the armoring layer for any given wind regime and grain size distribution the potential megaripple dimensions are limited by these two mechanisms here we study the first mechanism and estimate the duration of strong winds sustained above the fluid threshold needed to flatten megaripples strong gusts of wind in contrast cannot destroy the megaripples but can cause ripple migration based on data from previous works on megaripples we find a scaling law between the ripple morphology and the coarse mode of grains at the crest using this scaling relation allows us to calculate the wind velocity and duration needed for megaripple flattening in general the coarser the particles at the megaripple crest the stronger the wind needed to flatten the megaripples moreover the greater the strength of the wind required to flatten the megaripples the lower the recurrence probability taken together these findings increase the longevity of megaripples we apply the results for a megaripple field in the southern arava valley israel

surface deformation of westerly granite during creep holographic interferometry has been used to observe the surface deformation of westerly granite during creep experiments at 50 mpa 500 bars confining pressure interference fringes on the holograms produced by this technique constitute contour maps of the sample surface shape change between exposures several distinctive characteristics of the surface shape change have been observed in general surface deformation during primary and secondary creep while highly inhomogeneous is distributed fairly uniformly no large scale pattern is seen in the surface shape changes at approximately the onset of tertiary creep surface displacements become more locallized eventually approx 85 90 of time to failure a distinct ridge is formed which exactly coincides with the location of the final fracture

path dependence of acoustic velocity and attenuation in experimentally deformed westerly granite brittle failure in rocks is generally preceded by a localization of deformation in the region of the final macrofracture this process is associated with a non uniform distribution of subcritical microcracks which should be reflected in the distribution of acoustic velocities and surface deformation the temporal and spatial development of such deformation zones has been studied by monitoring these quantities during the deformation of westerly granite samples

a review on natural and human induced geohazards and impacts in karst karst environments are characterized by distinctive landforms related to dissolution and a dominant subsurface drainage the direct connection between the surface and the underlying high permeability aquifers makes karst aquifers extremely vulnerable to pollution a high percentage of the world population depends on these water resources moreover karst terrains frequently underlain by cavernous carbonate and or evaporite rocks may be affected by severe ground instability problems impacts and hazards associated with karst are rapidly increasing as development expands upon these areas without proper planning taking into account the peculiarities of these environments this has led to an escalation of karst related environmental and engineering problems such as sinkholes floods involving highly transmissive aquifers and landslides developed on rocks weakened by karstification the environmental fragility of karst settings together with their endemic hazardous processes have received an increasing attention from the scientific community in the last decades concurrently the interest of planners and decision makers on a safe and sustainable management of karst lands is also growing this work reviews the main natural and human induced hazards characteristic of karst environments with specific focus on sinkholes floods and slope movements and summarizes the main outcomes reached by karst scientists regarding the assessment of environmental impacts and their mitigation

true polar wander in mantle convection models with multiple mobile continents a b s t r a c t a r t i c l e i n f o the geologic record supports numerous instances during which continents apparently moved at speeds signi cantly faster than any of today s tectonic plates while the time dependence of convective driving forces likely explains some such observations rapid motions of large continents in particular are often attributed to true polar wander tpw in order to gauge the potential for connections between continents mantle temperature anomalies and polar motion we present the rst calculations of tpw derived from models that couple mantle convection with multiple mobile continents we nd that the aggregation and dispersal of supercontinents can lead to two types of tpw driven either by a well developed hot upwelling axis that creates a stable maximum moment of inertia or by the homogenization of mantle thermal structure following continent dispersal that leads to destabilization of the principal axis and possible large magnitude polar wander these supercontinent modulated thermal heterogeneities drive model tpw events as large as 90 at rates of up to 2 5 ma 1 such magnitudes and speeds are greater than those attained in similar models lacking continents but comparable to those for episodes inferred from paleomagnetic data for some large continents in the past published by elsevier b v on behalf of international association for gondwana research

the effect of wind speed averaging time on the calculation of sand drift potential new scaling laws abstract drift potential dp is a key factor used to quantify aeolian sand transport and it is often used for predicting wind erosion and dune mobility under climate change scenarios it is proportional to the mean of the cube of the wind speed at a 10 m height when that wind speed is above 6 2 m s 12 knots a speed threshold above which sand can be transported by the wind dp depends on the temporal resolution and the averaging time of the wind velocity measurements usually either a 10 min or 1 h mean wind speed is used to calculate the dp although different studies have used different averaging periods for calculating the mean wind speed and consequently the dp here we perform a comprehensive analysis of an extensive long term wind speed database from different locations around the world and from reanalysis data sources and show that dp decreases with the averaging time of the wind speed the decrease of dp versus the averaging time interval can be approximated by a stretched exponential function in addition the relative decrease of dp as a function of the maximum dp is smaller for high wind speed sites this result is a consequence of the fact that high dp sites are characterized by longer clusters of successive wind speed events above the threshold velocity they are thus less affected by the time averaging process interestingly the clusters lengths decay exponentially with wind speed and faster for low dp sites our new results have important implications for calculating the effective dp and for better estimating the biases that result from using wind data with different averaging times which is a common problem in aeolian research we also found an approximate linear relation between dp and the wind power that is close to the analytic approximation for the relation between the two this new finding has many important applications since it will allow one to calculate dp from wind power data and vice versa in addition it implies that the same scaling laws found for dp also exist for the wind power

ground motion and stress accumulation driven by density anomalies in a viscoelastic lithosphere some results for the apennines summary we provide the analytical formulation for calculating the displacement and stress field forced by internal sources in a stratified self gravitating viscoelastic earth this model is specialized to study the rate of vertical motion and shear stress accumulation produced by lithospheric density anomalies these sources are allowed to vary in the lateral direction we show that sphericity plays a crucial role for elongated lithospheric anomalies while self gravitation produces minor deviations from a gravitating earth when the model is applied to the apennines we get for lithospheric viscosity ranging between 10 and loz3 pas the subsidence of the plate underlying the active front of the overthrusting load to be around 0 5 1 0 mm yr this is consistent with the amount of sedimentation in the adriatic foredeep the deformation pattern is very peculiar with the largest subsidence localized beneath the active front of the topography our model enlightens the impact of discontinuities of tectonic phases on vertical motions in collision zones if lithospheric viscosity is around 10 pa s vertical motions decay drastically on time scales of 105yr if lateral migration of density anomalies comes to an end for higher viscosities deformation rates are maintained longer this correlation between horizontal and vertical motions suggests that altimetric geodetic surveying along levelling lines of a few hundred kilometers can be an important tool to constrain the tectonics of the studied region results are also shown for vertical motions along a transect perpendicular to the apennines when the crustal structure inverted from bouguer gravity data is considered analysis of the stress field induced by an overthrusting load shows that principal stress differences of a few bar or a few tenths of mpa can be accumulated on time scales of 102 103yr these low values agree with the average stress drop of earthquakes in the appalachians and northern apennines where our modelling can be applied we find that lateral density variations certainly contribute to intraplate stresses but they are less efficient in triggering earthquakes than other mechanisms such as transcurrent motions along active plate margins seismicity induced by lateral variations of crustal and lithospheric density must be moderate characterized by long return times these results are in agreement with the recorded seismicity in the northern apennines where the largest earthquakes have return times of lo2 yr if shear stress is forced by an overthrusting load we find that the largest rate of stress accumulation in the crust is concentrated beneath the active front close to the boundary with the ductile lithosphere discontinuities of tectonic phases play an important role in controlling the amount of shear stress due to density anomalies

subducted slabs and the geoid 1 numerical experiments with temperature dependent viscosity one of the most powerful constraints on mantle viscosity comes from the correlation of the long wavelength degree 4 9 geoid with that predicted by a density model for subducted slabs the effect of lateral variations of viscosity should be most pronounced at subduction zones due to the strong effect of temperature on viscosity an idealized slab model with temperature dependent viscosity is considered with various lateral and vertical viscosity structures using a two dimensional finite element formulation the viscosity parameterization affects the amplitude of the long wavelength geoid anomaly but not the sign of the correlation between the geoid and density anomalies depth dependent viscosity models with a high viscosity lithospheric layer do not completely match the temperature dependent laterally varying results suggesting that the rheology of the slab does have an effect on the long wavelength surface topography and geoid however this affect is minor suggesting that the radial models of mantle viscosity inferred from surface observables are correct to first order in contrast the short wavelength features are dramatically affected by the rheology of the region surrounding the downwelling further study of the shorter wavelength geoid over subduction zones may provide better insight into subduction zone processes

characteristics of near surface wind regimes in the taklimakan desert china abstract using wind data from 17 meteorological stations distributed throughout the taklimakan desert we described the characteristics of the desert s wind regimes and analyzed the spatial and temporal variations in wind direction and sand drift intensity the near surface wind regimes were closely related to general atmospheric circulation patterns and the surrounding topography there are two prevailing wind directions in the desert in general the eastern part of the desert is mainly affected by ne winds and the western part is affected by nw winds in the area towards the center of the desert but not around its edges the monthly mean wind velocity is strongly correlated with the monthly mean temperature with the exception of ruoqiang on the eastern edge of the desert the drift potential dp is less than 200 vu and the desert thus belongs to a low energy environment based on fryberger s classification in addition most parts of the desert have an rdp resultant dp dp value greater than 0 4 suggesting that the wind regimes have mainly unimodal or bimodal characteristics in contrast with the sand drift intensity which was highest in the north and east parts of the desert the highest frequency of sand dust storms occurred at the southwestern margin of the desert this results primarily from the differences of dust content on ground surfaces and land use types

the unique dynamics of the pacific hemisphere mantle and its signature on seismic anisotropy abstract the portion of earth s mantle lying below the hemispherical region occupied by the pacific ocean basin is characterized by a unique style of convection the unique dynamics below the pacific hemisphere are revealed by analyzing the mantle flow predicted on the basis of high resolution seismic images of mantle structure in the pacific hemisphere we find a dome like upwelling originating in the lower mantle which actively transports material into the upper mantle a unique aspect of this flow found only in the pacific hemisphere is a demi tour or u turn of the circulation which occurs in the shallow mantle west of the east pacific ridge this demi tour connects the westward movement of the pacific plate to the dome like upwelling below the central pacific ocean and it also provides an explanation for the asymmetric distribution of seismic anisotropy on either side of the ridge axis in a global analysis of the correlation between mantle flow and seismic anisotropy we find the strongest agreement occurs in the pacific hemisphere mantle

reactivation of supply limited dune fields from blowouts a conceptual framework for state characterization aeolian dune fields mantle the earth in both vegetated stable and unvegetated active states changes in state are poorly understood in particular little is known about reactivation devegetation from a vegetated state available evidence indicates that dune reactivation can be driven by changes in aridity increased wind speed fire biogenic disturbance human disturbance or a combination of the previous how these controls fit together and define the reactivation potential of dune fields is presently unknown here we develop a framework to describe reactivation potential for a specific case presently vegetated supply limited dune fields that develop blowouts under a unidirectional wind we first define a conceptual model of blowout expansion and then split the functions of vegetation in a stable dune field into i maintenance of a protective skin and ii blowout suppression we model reactivation as disturbance breaking through the protective skin which forms a blowout that is either i suppressed by colonizer species or ii capable of advancing downwind and reactivating part of the dune field the capacity for disturbance to break through the protective skin is a function of disturbance magnitude area and resistance of the skin the blowout suppression capacity of a dune field is a function of sediment flux blowout depth related to geomorphology and colonizer species vitality by plotting a given dune field with two variables protective skin breach rate and blowout suppression capacity we define four states i stable ii blowout dominated iii reactivating or iv stable but disturbance susceptible we reinforce the conceptual model with qualitative examples and discussion of experiments on grassland stabilized dunes in canada overall our framework provides a starting point for quantifying the reactivation potential of vegetated dune fields

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

implication for mantle flow from the hawaiian emperor chain abstract assuming that rayleigh benard flow occurs within the upper mantle ascending plumes must undergo horizontal displacement during ascent that can be traced at the surface it is shown that the hawaiian emperor bend cannot be formed if the convection rate is of the same order of magnitude as the ascent rate of the plumes the plume patterns obtained by push pull or lithospheric sliding are similar to that of the hawaiian emperor chain hence the present results support the sliding model

implications of an elastic analysis of in situ stress measurements near the san andreas fault twenty nine measurements of in situ stress obtained with the hydraulic fracturing technique near palmdale california are the basis of an elastic analysis of the state of stress in the mojave desert adjacent to the san andreas fault the measurements were made at depths extending from 80 to 849 m and at distances from the fault between 2 and 34 km the elastic solution indicates a state of deviatoric stress typical for continents in that the inferred depth gradient of the maximum shear stress is about 7 9 mpa km extrapolation yields an average shear stress in the upper 14 km of the crust of about 56 mpa a result that is higher than estimates of the average shear stress on the san andreas fault based on the analysis of heat flow data this finding is consistent however with estimates of fault strength based on laboratory determinations of the coefficient of friction for samples of san andreas fault gouge if the regional state of deviatoric stress is limited by the strength of the fault zone if so then the coefficient of friction of the san andreas fault zone inferred from the stress field results is about 0 45 the state of stress does not appear to vary systematically with distance from the san andreas fault although considerable localized variation is observed the observations suggest an upper bound of about 0 1 mpa km for the horizontal gradient of the maximum shear stress in the direction perpendicular to the san andreas fault a result that implies a corresponding limit of about 1 4 mpa on the shear traction applied to the base of the seismogenic layer finally we demonstrate the potential application of in situ stress data to the direct assessment of accumulated slip which could be released in a large earthquake we show that on the basis of a model involving a locked fault extending to about 22 km the total fault slip below the locked portion is less than 13 m a more comprehensive set of stress data could permit the estimation of an even lower bound

the spatial and temporal variability of sand erosion across a stabilizing coastal dune field this study aimed at quantifying the temporal and spatial variability in sand erosion and deposition over a coastal dune field in israel these were measured monthly over 2 years using 315 erosion pins over four transects that were placed perpendicular to the coastline vegetation cover was estimated based on aerial photographs and landsat satellite images whereas the relative height was based on a digital elevation model these variables were calculated for the area upwind south west of the erosion pins at various lengths ranging from 15 to 400 m nine geomorphologic units were defined five related to active units and four to stabilized units in active units at least 65 of the temporal variance in the annual absolute changes in sand level was explained by the index of resultant drift potential with most of the sand movement occurring during winter storms local rainfall had no apparent impact on sand mobility due to the low coincidence of sand carrying winds and rainfall in israel during the passage of frontal cyclones as for the spatial variables only a weak correlation was found between sand mobility with the distance from the coastline r 2 18 rather sand erosion and deposition were influenced by vegetation cover and the relative height of an area of 100 200 m upwind the values of soil adjusted vegetation index were significantly negatively correlated with annual absolute changes r 2 40 whereas the relative height was significantly positively correlated r 2 36 applying a multiple regression model 68 of the spatial variability in sand mobility was explained the resulting map of sand activity clearly shows that at this stage of the stabilization process most of the dunes are now disconnected and movement of sand grains from the beach or between the dunes is very limited these methods can be applied into spatial and temporal models of sand mobility thus assessing the impact of different management practices on coastal dunes

generation of plate tectonics with two phase grain damage and pinning source sink model and toroidal flow abstract the grain damage and pinning mechanism of bercovici and ricard 2012 for lithospheric shear localization is employed in two dimensional flow calculations to test its ability to generate toroidal strike slip motion and influence plate evolution this mechanism posits that damage to the interface between phases in a polycrystalline material like peridotite composed primarily of olivine and pyroxene increases the number of small zener pinning surfaces which then constrain mineral grains to ever smaller sizes regardless of creep mechanism this effect allows a self softening feedback in which damage and grain reduction can co exist with a grain size dependent diffusion creep rheology moreover grain growth and weak zone healing are greatly impeded by zener pinning thereby leading to long lived relic weak zones the fluid dynamical calculations employ source sink driven flow as a proxy for convective poloidal flow upwelling downwelling and divergent convergent motion and the coupling of this flow with non linear rheological mechanisms excites toroidal or strike slip motion the numerical experiments show that pure dislocation creep rheology and grain damage without zener pinning as occurs in a single phase assemblages permit only weak localization and toroidal flow however the full grain damage with pinning readily allows focussed localization and intense plate like toroidal motion and strike slip deformation rapid plate motion changes are also tested with abrupt rotations of the source sink field after a plate like configuration is developed the post rotation flow and material property fields retain memory of the original configuration for extensive periods leading to suboptimally aligned plate boundaries e g strike slip margins non parallel to plate motion oblique subduction and highly localized weak and long lived acute plate boundary junctions such as at what is observed at the aleutian kurile intersection the grain damage and pinning theory therefore readily satisfies key plate tectonic metrics of localized toroidal motion and plate boundary inheritance and thus provides a predictive theory for the generation of plate tectonics on earth and other planets

renormalisation of global mantle dynamic topography predictions using residual topography measurements for normal oceanic crust abstract we compare mantle dynamic topography predicted from mantle convection modelling with residual topography measurements for oceanic regions where crustal basement thickness is 10 0 km or less measurements of residual topography calculated by removing the isostatic effects of crustal thickness variation bathymetry sediments ice and lithosphere thermal anomalies from the observed topography are inaccurate for continents and oceanic plateaus due to uncertainties in determining their crustal thickness and density as a consequence residual topography measurements for these regions are unsuitable for testing mantle dynamic topography predictions residual topography is more accurately determined for oceanic crust we use global mapping of crustal basement thickness using gravity anomaly inversion to identify oceanic crust of 10 0 km thickness or less to select measured residual topography for comparison with predicted mantle dynamic topography for these oceanic regions we compare mantle dynamic topography and residual topography and using amplitude histogram matching and grid searches compute the amplitude rescaling and shift which needs to be applied to predicted mantle dynamic topography to fit the observed residual topography we examine three global compilations which use different approaches to determine mantle dynamic topography i steinberger 2007 which uses seismic topography deeper than 220 km to determine mantle density ii flament et al 2013 which uses plate velocity and subduction history and iii steinberger et al 2017 which uses seismic tomography including that above 220 km to determine shallow upper mantle densities our analysis shows that for the steinberger 2007 and flament et al 2013 compilations the predicted mantle dynamic topography for oceanic regions requires a rescaling of approximately 0 5 and a negative shift of approximately 500 m to match the observed residual topography in contrast steinberger et al 2017 which includes shallow upper mantle densities above 220 km requires only a small shift 50 m but a greater scaling of 0 375 maps of renormalised rescaled and shifted mantle dynamic topography for steinberger et al 2017 show a close resemblance to measured residual topography

water leakage paths in the doosti dam turkmenistan and iran the doosti dam with a reservoir capacity of 1 250 million cubic meters was constructed on the harirood river at the border of turkmenistan and iran the reservoir is in direct contact with permeable formations on the right abutment of the dam including the neyzar sandstone the kalat limestone and the pesteleigh alternative layers of marlstone and sandstone after the reservoir impoundment several new springs and seepages emerged from these formations and the alluvium the amount of leakage increased with the rise in reservoir water level fifteen kilograms of sodium fluorescein were injected into a 113 m deep borehole intersecting three permeable sandstone layers of the pesteleigh formation dye was detected downstream of the grout curtain in boreholes and springs that were in direct contact with parts of the pesteleigh formation having the same sandstone layers as the injection borehole the dye velocity was in the range of diffuse flow confirming the good performance of the grout curtain in the pesteleigh formation no dye was detected in the other formations because the injection borehole was not in direct contact with these formations the hydraulic relation of the other formations with the reservoir was determined by considering direct contact of the formations with the reservoir emergence of new springs and seepages after reservoir impoundment correlation of time variations of the springs discharge and the borehole s water level with the reservoir water level and in some cases the hydrochemistry of the water the results show that the kalat and neyzar formations are hydraulically connected to the reservoir but the small amounts of leakage from these formations at a hydraulic gradient of 24 indicates good performance of the built grout curtain the total reservoir leakage at maximum reservoir water level was 100 l s which is insignificant compared with the 15 m3 s average annual release of the reservoir

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

method of leakage study at the karst dam site a case study khersan 3 dam iran the excellent topographic condition of the limestone canyons for dam construction may be rejected if they are karstified karst features cause the reservoir not to be impermeable enough to permit the water to fill it and leakage occurs and often increases with time moreover karst features may involve the stability of the dam itself a few operated dam sites at the zagros zone encountered a leakage problem furthermore more than 30 dams are presently under study for construction in the zagros zone karst conditions and leakage potential were investigated at an under study site khersan 3 dam for assessing the general methodology for the study of leakage potentials conventional methods for studying karst features geological mapping geomorphology and extensive borings were applied before the dam was constructed these methods are not efficient enough to precisely reveal the karst structure especially hidden and paleokarst nor the hydrological behaviour of the karst structure in different settings of groundwater flow based on the present case study and previous applied approaches by other authors this paper introduces a methodology by means of karst structure and functioning approaches at local and regional scales that cover the conventional methods and overcome their shortages the proposed methodology should be applied before construction of a dam and should include three steps a recognition of geological and hydrogeological settings b delineation and functioning of the karst system related to the future reservoir and c assessment of the leakage potentials following this methodology the most probable leakage zone s and path s at the dam site can be highlighted

dam sites in soluble rocks a model of increasing leakage by dissolutional widening of fractures beneath a dam abstract water flowing through narrow fissures and fractures in soluble rock e g limestone and gypsum widens these by chemical dissolution this process called karstification sculptures subterranean river systems which drain most of their catchment close to dam sites unnaturally high hydraulic gradients are present to drive the water impounded in the reservoir downstream through fractures reaching below the dam under such conditions the natural process of karstification is accelerated to such an extent that high leakage rates may arise which endanger the operation of the hydraulic structure model simulations of karstification below dams by coupling equations of dissolutional widening to hydrodynamic flow are presented the model scenario is a dam 100 m wide in limestone or gypsum the modelling domain is a two dimensional slice 1 m wide directed perpendicular to the dam it extends 375 m vertically and 750 m horizontally the dam is located in its center this domain is divided by fractures and fissures into blocks of 7 5 7 5 1 m the average aperture width of the fractures is 0 02 cm we performed model runs on standard scenarios for a dam site in limestone with the height h of impounded water 150 m a horizontal impermeable apron of width w 262 m and a grouting curtain reaching down to a depth of g 97 m in a second scenario we changed these construction features to g 187 m and w 82 m to calculate widening of the fractures well established experimental data on the dissolution of limestone and gypsum have been used as they occur in such geochemical settings all model runs show similar characteristic behaviour shortly after filling the reservoir exhibits a small leakage of about 0 01 m 3 s 1 which increases steadily until a breakthrough event occurs after several decades with an abrupt increase of leakage to about 1 m 3 s 1 within the short time of a few years then flow in the fractures becomes turbulent and the leakage increases to 10 m 3 s 1 in a further time span of about 10 years the widths of the fractures are visualized in various time steps small channels propagate downstream and leakage rises slowly until the first channel reaches the surface downstream then breakthrough occurs the laminar flow changes to turbulent and a dense net of fractures which carry flow is established we performed a sensitivity analysis on the dependence of breakthrough times on various parameters determining breakthrough these are the height of impounded water h the depth g of grouting the average aperture width a 0 of the fractures and the chemical parameters which are c eq the equilibrium concentration of ca with respect to calcite and the ca concentration c in of the inflowing water the results show that the most critical parameter is a 0 at fracture aperture widths of 0 01 cm breakthrough times are above 500 years for values of a 0 0 02 cm however breakthrough times are within the lifetime of the structure we have also modelled dam sites in gypsum which exhibit similar breakthrough times however after breakthrough owing to the much larger dissolution rates of gypsum the time until unbearable leakage is obtained is only a few years the modelling can be applied to complex geological settings as phreatic cave conduits below the dam or a complex stratigraphy with varying properties of the rock with respect to hydraulic conductivity and solubility a few examples are given in conclusion our results support the assumption that increasing leakage of dam sites may be caused by dissolutional widening of fractures

interaction between a dam site and karst springs the case of supramonte central east sardinia italy abstract sardinia is one of the italian regions with the greatest number of dams per inhabitants almost 60 for a population of only 1 5 million people many of these dam sites are located on non carbonate rocks along the main rivers of the island and their waters are used for irrigation industrial energy supply drinking and flood regulation purposes the pedra e othoni dam on the cedrino river dorgali central east sardinia is located along the threshold of the palaeozoic basement on the northern border of the supramonte karst area where water is forced to flow out of the system through several resurgences the most famous of which is the su gologone vauclusian spring used for drinking water supply the other main outflows of the system su tippari and san pantaleo springs are at present almost permanently submerged by the high water level of the pedra e othoni dam in the near future water will be supplied also to other communities with a possible increase of water taken from the spring the dam originally meant to regulate the flooding of cedrino river but actually used for all sorts of purposes electricity supply drinking water irrigation of farmlands industrial uses has a maximum regulation altitude of 103 m a s l only slightly less than a meter below the su gologone spring level 103 7 m and 4 and 9 m respectively above the submerged su tippari and san pantaleo springs during floods of the cedrino river occurring on average twice a year also the su gologone spring becomes submerged by the muddy waters of the lake for a time ranging between a couple of hours up to several days making water supply impossible the analysis of the available meteorological and hydrogeological data relative to the december 2004 flood one of the severest of the past 100 years suggests that the reservoir is filled in a few days time several flooding scenarios have been reconstructed using digital terrain models showing that backflooding submerges most of the discharge area of the aquifer having important repercussions also on the inland underground drainage system the upstream flood prone areas prevalently comprise agricultural lands with some sparse houses but also highly frequented tourist facilities fortunately flooding occurs outside the tourist season thus limiting risk to a limited number of local inhabitants massive discharge at the dam site instead determines a more hazardous situation in the cedrino coastal plain where population density in low lying areas is much higher to avoid flooding hazard upstream the water level in the lake should be regulated keeping it low in the flood prone seasons and having it filled from the end of the winter in order to have enough water stocked before the beginning of the summer discharge at the dam site instead should be done cautiously preventing severe flooding of the coastal cedrino plain

time dependent convection models of mantle thermal structure constrained by seismic tomography and geodynamics implications for mantle plume dynamics and cmb heat flux summary one of the outstanding problems in modern geodynamics is the development of thermal convection models that are consistent with the present day flow dynamics in the earth s mantle in accord with seismic tomographic images of 3 d earth structure and that are also capable of providing a time dependent evolution of the mantle thermal structure that is as realistic earth like as possible a successful realization of this objective would provide a realistic model of 3 d mantle convection that has optimal consistency with a wide suite of seismic geodynamic and mineral physical constraints on mantle structure and thermodynamic properties to address this challenge we have constructed a time dependent compressible convection model in 3 d spherical geometry that is consistent with tomography based instantaneous flow dynamics using an updated and revised pseudo spectral numerical method the novel feature of our numerical solutions is that the equations of conservation of mass and momentum are solved only once in terms of spectral green s functions we initially focus on the theory and numerical methods employed to solve the equation of thermal energy conservation using the green s function solutions for the equation of motion with special attention placed on the numerical accuracy and stability of the convection solutions a particular concern is the verification of the global energy balance in the dissipative compressible mantle formulation we adopt such validation is essential because we then present geodynamically constrained convection solutions over billion year timescales starting from present day seismically constrained thermal images of the mantle the use of geodynamically constrained spectral green s functions facilitates the modelling of the dynamic impact on the mantle evolution of 1 depth dependent thermal conductivity profiles 2 extreme variations of viscosity over depth and 3 different surface boundary conditions in this case mobile surface plates and a rigid surface the thermal interpretation of seismic tomography models does not provide a radial profile of the horizontally averaged temperature i e the geotherm in the mantle one important goal of this study is to obtain a steady state geotherm with boundary layers which satisfies energy balance of the system and provides the starting point for more realistic numerical simulations of the earth s evolution we obtain surface heat flux in the range of earth like values 37 tw for a rigid surface and 44 tw for a surface with tectonic plates coupled to the mantle flow also our convection simulations deliver cmb heat flux that is on the high end of previously estimated values namely 13 tw and 20 tw for rigid and plate like surface boundary conditions respectively we finally employ these two end member surface boundary conditions to explore the very long time scale evolution of convection over billion year time windows these billion year scale simulations will allow us to determine the extent to which a memory of the starting tomography based thermal structure is preserved and hence to explore the longevity of the structures in the present day mantle the two surface boundary conditions along with the geodynamically inferred radial viscosity profiles yield steady state convective flows that are dominated by long wavelengths throughout the lower mantle the rigid surface condition yields a spectrum of mantle heterogeneity dominated by spherical harmonic degree 3 and 4 and the plate like surface condition yields a pattern dominated by degree 1 our exploration of the time dependence of the spatial heterogeneity shows that for both types of surface boundary condition deep mantle hot upwellings resolved in the present day tomography model are durable and stable features these deeply rooted mantle plumes show remarkable longevity over very long geological time spans mainly owing to the geodynamically inferred high viscosity in the lower mantle

a step wise semi distributed simulation approach to characterize a karst aquifer and to support dam construction in a data scarce environment abstract karst systems provide significant volumes of drinking water for large parts of the world population due to chemical weathering karst systems are characterized by strong heterogeneity resulting in a complex flow and storage behaviour presently available karst modelling strategies account for the karstic heterogeneity but often a lack of data limits their applicability in data scarce regions in this study a step wise simulation approach with a semi distributed karst model is proposed to characterize a karst aquifer at a data scarce region in southwest iran and to evaluate the leakage potential related to a future dam construction project at a river that cuts through the aquifer observed groundwater level time series were applied to calibrate and validate the model in order to avoid over parameterization the karst aquifer was split into three sections down the hydraulic gradient at each section groundwater level observations were used to iteratively calibrate the model from the first to the last section a spatial split sample test and sensitivity analysis served to evaluate the prediction performance and the identifiability of the model parameters finally simple scenarios of the river infiltration into the aquifer were applied to evaluate the leakage potential of the aquifer for future dam constructions the spatial split sample test showed that the semi distributed model provided reliable predictions but prediction performance and parameter identifiability decreased from the first towards the last aquifer section most probably due to increased aquifer complexity and propagation of uncertainty from the up gradient model section using sensitivity analysis we also show that parameter sensitivities increase significantly if parameter estimation was applied simultaneously to all three aquifer subsections using the model to assess the leakage potential indicated that without further technical measures the all river flow would be able infiltrate into the aquifer and the dam would never be filled up completely

holographic in situ stress measurements a new instrument for measuring the in situ level of stress in boreholes has been developed the instrument operates on the principle of locally relieving the stresses acting on a rock mass by drilling a small hole into the borehole surface and recording the resultant displacement field by holographic interferometry because the recording technique is optical the entire displacement field due to stress relief is obtained a description of the stressmeter theory of the interferometric technique data reduction methodology and results of laboratory stress relief calibration tests are presented in addition we present results from a field deployment of the instrument in an underground shale mine in garfield county colorado using a test borehole within a support pillar sufficient data were obtained to constrain five of six stress components at a shallow level of the test borehole thereby demonstrating the viability of the holographic technique the holographic stress relief data yield an approximate ew maximum horizontal stress direction by comparison with previous hydrofracture measurements of bredehoeft et al our results indicate substantial stress relief near the pillar face thus masking any relicts of the far field tectonic stress

the effect of rheological parameters on plate behaviour in a self consistent model of mantle convection abstract in a three dimensional numerical model of mantle convection we have explored the self consistent formation and evolution of plates this was done by investigating the influence of temperature stress and pressure dependence of the viscosity on plate like behaviour further the role of a depth dependent thermal expansivity and of internal heating was examined first order self consistent plate tectonics can be obtained for temperature and stress dependent viscosity we observe virtually undeformed moving plates and the phenomenon of trench migration however plate motion only appears during short intervals which are interrupted by long phases characterised by an immobile lid an improvement is achieved by adding pressure dependence of the viscosity and of the thermal expansivity to the model this leads to extended plates with continuous plate motion and the appearance of a low viscosity zone internal heating accelerates subduction and gives an increase in plate velocity the plates are otherwise left intact we find that the surface velocity is largely determined by subduction rather than by upwellings plate like behaviour is restricted to a narrow parameter window the window is bordered by an episodic or a stagnant lid type of flow on the one side and by a domain in which convection is akin to constant viscosity flow on the other side with these different convective regimes the behaviour of various terrestrial planets can be described self consistently occasionally even a change from the plate regime to the stagnant lid regime occurs such a type of transition has possibly changed the style of tectonics on some terrestrial planets such as mars

subduction zones observations and geodynamic models abstract this review of subduction and geodynamic models is organized around three central questions 1 why is subduction asymmetric 2 are subducted slabs strong or weak 3 how do subducted slabs interact with phase transformations changes in mantle rheology and possibly chemical boundaries in the mantle based on laboratory measurements of the temperature dependence of olivine one would conclude that the core of a subducting slab is at least 10 000 times more viscous than ambient mantle however there are a number of complementary but independent observations that suggest that slabs are much weaker than this slabs undergo significant deformation in the upper mantle and may thicken to twice their original width by the time they reach the base of the transition zone the lack of a clear correlation between the observed dip angle of deep slabs and plate velocity rate of trench migration and slab age in modern subduction zones is consistent with hypothesis that subduction is a time dependent phenomenon both tank and numerical convection experiments with plates conclude that subduction is not a steady phenomenon but that slabs bend thicken stretch and change dip through time this is at odds with the assumptions used in steady state slab thermal models where slab deformation is not considered

back arc spreading in the proterozoic a theoretical approach abstract the early proterozoic earth probably had a hotter mantle and a lower residence time for oceanic plates at the surface than the modern one the hotter mantle may have led to thinner oceanic plates young ocean floor has low negative buoyancy and therefore exerts low slab pull forces in subduction zones this effect would have been greater if the plates were thinner since they would have warmed up more quickly as they descended into the mantle thus the negative buoyancy of slabs and the slab pull forces were probably substantially lower in the early proterozoic calculations show that this applies even if subduction rates were higher and the crust was thicker lower slab pull leads to lower rates of rollback in subduction zones and lower rates of retreat of upper plates from trenches the limited age range of oceanic crust and the more rapid heating of descending slabs in subduction zones probably leads to a smaller range of slab profiles since this range is controlled by thermal properties of the slab and therefore to more stability in subduction zones thus many of the proposed mechanisms for back arc spreading may have been less effective and backarc spreading may have been less common in early proterozoic subduction zones this may explain the apparent absence of ophiolite complexes of that age

a note on the use of the fryberger method for evaluating potential sand transport by wind the fryberger method provides a useful and accessible way of evaluating potential sediment transport by wind in this method an equation is used to estimate relative rates of sand transport expressed as drift potential from measurements of wind velocity however the values of drift potential obtained through the calculations are dependent upon the units in which wind velocities are expressed this paper highlights some of the confusion this dependence can cause and aims to clarify the ways in which values of drift potential can be interpreted

laser holographic measurements of tidal deformation of a tunnel summary a new technique based on holographic interferometry has been developed for measuring crustal deformations the holographic recording system consisting of an he ne gas laser and associated optical elements was first installed in a tunnel at the amagase crustal movement observatory in 1984 tunnel deformations caused by tidal and tectonic forces have been precisely determined using the real time technique of holographic interferometry in this procedure a hologram of the tunnel wall within a section 1 2 m in diameter is directly recorded on a photographic plate and then the plate is carefully reset in the position at which the hologram was taken when the reconstructed image of the hologram is superimposed on the current image of the tunnel wall many interference fringes can be seen through the hologram the fringe displacement formed by the deformation of the tunnel is continuously recorded on a video cassette tape using a video camera and a time lapse video recorder the change in the fringe patterns is analysed using the image processing system tidal deformations obtained from the holographic method are consistent with the strain changes observed with laser extensometers in the same tunnel these observational results substantiate the tunnel deformation estimated by finite element calculations

investigation of leakage at ataturk dam and hydroelectric power plant by means of hydrometric measurements abstract ataturk dam with its 84 5 million m 3 fill volume and 169 m height above the foundation is one of the largest dams in the world its 1 2 million m 2 grout curtain surface area is the largest constructed in the world to date the bozova fault crosses the dam axis in the left bank and extends towards the downstream valley the grout curtain constructed in karstic limestone is 180 m deep in the thalweg and partially extends to 250 300 m depths in some local zones on both the right and left sides of the valley in this study we have investigated leakage at the ataturk dam and hydroelectric power plant by means of hydrometric measurements the hanging grout curtain indicates that leakage at ataturk dam is of vital importance in defining the longevity of the dam hydrometric measurements including discharge temperature and electrical conductivity of springs and leakages were carried out for 9 years periodically in addition to monitoring performed before during and after construction the leakage increased as the reservoir water level rose seasonally but it was also discovered that this regular increase was not observed in the last three measurements the decrease in leakage volume in the last three measurements proved the integrity of the grout curtain and the efficiency of the microsol grout works recent seepage levels are within design limits and therefore have no serious effect on the stability of the dam structures

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

characteristics of wind blown sand in the region of the crescent moon spring of dunhuang china based on the detailed wind data this paper aims to investigate wind regime drift potential and the movement of mega dunes at the crescent moon spring an important scenic spot in western china and to clarify the dominant factors that control sand transport in this region the results of this paper revealed that the dominant wind directions at the spring were nw and sw the spring region belonged to a low energy wind environment the wind regime and sand drift potential were hugely influenced by local topography and the regional atmospheric circulation intensified the complexity of their variations besides the movement of the southern and northern mega dune towards the spring greatly endangered the preservation of this scenic spot these results provide insights into the characteristics of wind blown sand at the crescent moon spring that will guide efforts to control sand damages

on the forces driving plate tectonics inferences from absolute plate velocities and intraplate stress summary absolute plate motions and intraplate stress both serve as tests of models for the forces acting on plate boundaries plate velocities relative to a presumedly fixed underlying mantle are calculated from the hypothesis that no net torque is exerted on the lithosphere intraplate stress is calculated by solving the equilibrium equations for thin elastic shells in the membrane state of stress the absolute velocity fields predicted from a wide assortment of physical and geological models are all very similar while the global pattern of absolute velocity is probably close to those predicted by such models the absolute motions do not therefore provide a strong test of the driving mechanism comparison of predicted intraplate stress with the long wavelength features of the global stress field however as determined by in situ measurements earthquake mechanisms and stressinduced geological structures does prove to be a powerful test of possible driving forces all absolute velocity models have several interesting properties lithosphere in the equatorial half of the earth is moving significantly faster than lithosphere in the polar half some connection to the earth s rotation is implied since this statement is demonstrably untrue for co ordinate poles much different from the geographic pole subducted slabs are characterized by a slow horizontal translation perpendicular to strike that is independent of the plate convergence rate confounding attempts to explain the dip angles of benioff zones in terms of a uniform vertical sinking and a variable absolute velocity for the overthrust plate ridges must migrate at a wide range of velocities relative to their underlying source of new lithosphere such rapid migration may be a necessary but is not a sufficient condition for ridge jumps force models considered in velocity and stress calculations include driving forces at spreading centres and subduction zones and various parameterizations of drag at the base of the lithosphere from the rms absolute velocities of individual plates there is a weak indication that pull by subducted lithosphere at trenches is an important driving force and that drag may be greater beneath continental than oceanic lithosphere the predicted intraplate deviatoric stress cannot match the well determined stress fields in north america and europe unless the driving force exerted at ridges is at least comparable in magnitude to other forces in the system the mid plate stresses are very sensitive to the nature of drag at the base of the lithosphere and thus measured stresses may ultimately provide a sensitive test of absolute plate velocities

seepage problems in the karstic limestone foundation of the kalecik dam south turkey abstract seepage phenomena through the karstic limestone foundation of kalecik dam are investigated the dam designed as a rock fill dam with a height of 77 m is already used for irrigation the foundation consists of mesozoic ophiolite paleocene allochthonous units composed of different lithologies and miocene conglomerate the conglomerate lies unconformably on the other units quaternary basaltic lava patchily covers the others seepage from upstream to downstream occurs through the allochthonous karstic limestone this limestone which is overlain by conglomerates has a thickness increasing towards the right abutment to prevent seepage at the right abutment a 200 m long and 60 m deep grout curtain along the dam axis was constructed after the impoundment some springs occurred downstream and for this reason extra grouting was performed however the seepage problem could not be solved in order to determine the seepage direction and karstification pattern hydrological studies have been done additional investigation boreholes have been drilled to observe fluctuations of the groundwater level and to analyze hydrochemistry also dye tracer tests have been carried out as a result of these hydrogeological studies seepage paths were observed in the karstic limestone located between the dam and the spillway as those carbonate rocks continue beneath the spillway the seepage problems are enjected to continue

hydrologic characteristics of a large rockfill dam implications for water leakage abstract the unmun dam a rockfill dam with a clay core filter zone and sandy gravel shell is located in the nakdong river basin near cheongdo gun in korea in the dam area the cretaceous gyeongsang supergroup andesite lies over intrusive granite these form the intrusive contact near the main dam and cofferdam areas the stratigraphic units in upward sequence consist of cretaceous granite and andesite weathered soft rock and a soil layer of silty clay with gravel the reservoir was first filled in august 1994 and was full by april 1998 right after complete filling three sinkholes were found in the dam crest near stations 2 12 and 10 when the reservoir level was at around 150 m the amount of leakage increased with rise of the reservoir level mainly caused by rainfall events as a countermeasure for the abnormal leakage and dam rehabilitation comprehensive surveys were performed on the dam including observational drillings grouting geophysical surveys and tracer tests by korea water resources corporation kowaco there were also further investigations for hydrologic characterization of the dam to identify water leakages the groundwater levels at the 26 observation wells installed on the crest and dam toe were measured to evaluate the relationship between the reservoir level and groundwater level and the influences on the dam leakage groundwater level at the left side of the embankment was high compared with a normal phreatic line it was only 4 m lower than the reservoir level while 6 65 m lower than that at its right side fluctuation of the groundwater levels in the crest wells coincided well with the reservoir level without a significant lag time which reflected a good hydraulic connection between the reservoir and the dam interior hydraulic conductivity estimated from 149 hydraulic tests at 9 monitoring wells constructed in the dam core showed a wide range between 1 42 10 4 and 4 35 10 8 cm s with a geometric mean of 3 13 10 6 cm s furthermore water quality at the monitoring wells were much different from that of the reservoir high levels of turbidity and electrical conductivity were observed at the monitoring wells in the left side of the bank all these hydrologic characteristics reflected possible occurrence of the leakage on the dam especially in the left embankment this paper presents a summary of several investigation studies on the hydrologic characteristics of the rockfill dam which implied abnormal water leakage

seepage problems in the right abutment of the shahid abbaspour dam southern iran abstract in this study seepage phenomena through the right abutment of shahid abbaspour dam are investigated the shahid abbaspour dam is a 200 m high arch dam which regulates the waters of the karun river serves power generation and flood control and irrigation needs the dam site lies in the zagros mountains of southern iran this region presents continuous series of mainly of karstic limestone marl shale and gypsum ranging in age from jurassic to pliocene the region has subsequently been folded and faulted seepage from the shahid abbaspour reservoir occurs mainly through the karstic limestone the basic foundation treatment of the dam consisted of consolidation grouting a high pressure grout curtain and a drainage curtain moreover a 144 m high and 30 m wide concrete cutoff wall was built to prevent reservoir seepage through a clay filled fracture zone in the right abutment the grout curtain penetrates the principal vuggy zone only beneath the central portion of the dam and below the cutoff wall in the right abutment fan curtains were constructed to reduce drainage flows but the seepage problem could not be solved in order to determine the seepage direction and karstification pattern hydrogeological studies have been carried out additional investigation boreholes have been drilled to monitor fluctuations in groundwater level besides these water chemistry dye tracer pinhole and xrf tests have been carried out as a result of these studies seepage paths have been identified in the karstic limestone in the right abutment of the dam

trench motion slab geometry and viscous stresses in subduction systems summary a semi analytic 3 d model for subduction within a newtonian viscous upper mantle provides a dynamically consistent means of computing viscous stress trench motion and slab geometry in subduction systems although negative slab buoyancy provides the basic driving force for subduction slabs that extend from the surface to the base of the upper mantle are oversupported by viscous stresses in the shallow 100 150 km mantle and undersupported by viscous stresses at greater depth in the upper mantle these deeper parts of the subduction system act as an engine for subduction while shallower parts act as a brake on trench motion trench migration rates and slab geometry reflect a competition between these two effects during steady state subduction trench migration rates vary approximately linearly with slab buoyancy and model rates of trench motion are in good agreement with the range of observed rates for a two layer upper mantle viscosity of 2 10 20 pa s above 300 km and 5 10 20 pa s below steady state slab dip increases as slab density decreases especially for very low density slabs which dip significantly more steeply than high density slabs the horizontal velocity at the top of the lower mantle measured relative to the foreland has a very large effect on trench migration rates rivalling or even exceeding that of slab buoyancy slab width parallel to the trench also has a significant effect on trench migration rates due to the viscous pressure of toroidal flow around the slab the stiffness of the subducting lithosphere does not exert a significant effect on trench migration rates or slab geometries for rigidities compatible with oceanic lithosphere very stiff slabs with elastic plate thicknesses more that 40 km or viscosities in the range of 10 25 10 26 pa s subduct significantly more slowly than weak slabs with trench migration rates in the range of half to a third that of weak slabs large unexpected effects on trench migration rates and slab geometry are exerted by the structure and density of the frontal prism and overriding plate indicating that local geology can exert important constraints on slab dynamics during non steady state subduction rates of trench migration respond rapidly as variably buoyant lithosphere penetrates into the asthenosphere in the absence of other driving forces for convergence trench migration rates can change by a factor of two or more in as little as 2 3 myr for example from 35 to 70 mm yr 1 when an oceanic piece of slab follows a continental one into the subduction system subduction of variable buoyancy lithosphere is accompanied by changes in slab dip with depth and through time

a critical assessment of viscous models of trench topography and corner flow stresses for newtonian viscous flow in a simple geometry e g corner flow bending flow are obtained in order to study the effect of imposed velocity boundary conditions stress for a delta function velocity boundary condition decays as 1 r 2 for a step function velocity stress goes as 1 r for a discontinuity in curvature the stress singularity is logarithmic for corner flow which has a discontinuity of velocity at a certain point the corresponding stress has a 1 r singularity however for a more realistic circular slab model the stress singularity becomes logarithmic thus the stress distribution is very sensitive to the boundary conditions and in evaluating the applicability of viscous models of trench topography it is essential to use realistic geometries topography and seismicity data from northern hoshu japan were used to construct a finite element model with flow assumed tangent to the top of the grid for both newtonian and non newtonian flow power law 3 rheology normal stresses at the top of the grid are compared to the observed trench topography and gravity anomalies there is poor agreement purely viscous models of subducting slables with specified velocity boundary conditions do not predict normal stress patterns compatible with observed topography and gravity elasticity and plasticity appear to be important for the subduction process

wind regimes and aeolian transport in the great basin u s a abstract the modern great basin of the interior western united states is characterized by surface winds with considerable spatial and temporal variabilities wind records from the second half of the 20th century for 12 great basin localities analyzed with standard aeolian sediment transport methods developed elsewhere in the world reflect this complexity the drift potential dp for aeolian deposits is generally moderate dp 200 400 in the western great basin and weak dp 300 at the eastern edge of the great basin where the dominant prevailing wind direction is south southwesterly both dp and resultant drift direction rdd are consistent with synoptic meteorological observations of the evolution of cold fronts in the great basin meteorological observations show that effective winds to produce dunes are most commonly the result of late winter early spring cyclogenesis there has been considerable temporal variability of dp in the latter half of the 20th century most of the great basin has experienced decreasing wind strength since 1973 consistent with recent studies of wind strength in north america and elsewhere dune morphology matches both localized rdd and temporal variations in dp reasonably well in the great basin the results demonstrate that local topography can have an important influence on wind directionality thus providing a cautionary note on the interpretation of dune morphology in the paleoclimatic and stratigraphic record

morphodynamics and climate controls of two aeolian blowouts on the northern great plains canada blowouts are the most regionally pervasive active aeolian landform on the northern great plains of north america this study reports a long term investigation into the morphological development of two adjacent blowouts in a continental dune field the blowouts were monitored for a decade in the bigstick sand hills of southwestern saskatchewan canada topographic changes were determined from dense arrays of erosion pins in each blowout 1 per 4 m2 n 171 and 1 per 16 m2 n 150 pin measurements were made 16 times between may 1994 and may 2004 over the decade both blowouts expanded and more than doubled in volume differences in form flow interactions have caused the larger of the two blowouts to deposit more than a metre of sediment within the deflation basin and the smaller blowout to erode by more than a metre a negative feedback effect was triggered when the larger blowout reached a critical size around 1994 60 m 36 m 8 1 m length width height when sediment was no longer eroded from the deflation basin a positive feedback in the smaller blowout continues to facilitate erosion from the deflation basin monthly observations since 2002 indicate that aspect plays an important role in the development of these blowouts by creating a spatial asymmetry in sediment availability sediment is more readily available throughout the year on south facing slopes which receive greater insolation than north facing slopes and are often drier and more frequently thawed in this cold climate environment comparisons between climate data from a remote meteorological station 45 km to the southwest and sediment transport indices developed from the erosion pin data produced very few correlations significant at the 95 per cent confidence level nevertheless the signs of the correlation coefficients indicate that sediment erosion and deposition in both blowouts respond similarly to the following climate variables recorded at the remote station i the amount of precipitation ii the transport capacity of the wind and iii transporting winds from a directional wedge between 180 and 330 taken altogether the results from this study highlight the importance of climate and feedback effects in blowout development that may be extended to other blowouts in continental and coastal settings copyright 2006 john wiley sons ltd

speculations on the thermal and tectonic history of the earth summary the connection between the earth s thermal history and convection in the mantle is exploited to elucidate the early evolution of the earth it appears probable that convection extending over almost all of the mantle has dominated vertical heat transport throughout the whole of the earth s history only in boundary layers at the surface and at a depth of 650 700 km is conduction likely to be important the resulting evolution appears to be consistent with geological observations on early precambrian rocks various arguments are put forward in favour of two horizontal scales of convective flow in the mantle at depths less than 650 km the large scale flow is related to the motion of major plates and must be ordered over distances of more than 5000 km its evolution and energetics are discussed and there are no obvious problems in maintaining the proposed convective motions small scale flow with an extent of the order of 500 km appears necessary both to explain the heat flow through older parts of the earth s surface and to reconcile the geophysical observations with the results of numerical experiments though the existence of the small scale flow is at present speculative various tests of its presence are proposed

the lar dam an example of infrastructural development in a geologically active karstic region abstract the problems associated with the construction of the lar dam iran provide a classic example of problems that can result from infrastructural development in an active geological terrain which includes the regional carbonate units the lar dam lies in a heavily faulted and fractured region close to the active damavand volcano the fracturing has enhanced the production of karst and sinkholes in the limestone below the dam and acidic ground water run off from the damavand volcano increases the dissolution of the carbonate beds along the fractures to produce sinkholes below the dam the initial problem of building the dam in such a region is compounded by the relationship between water loss due to enhanced sinkhole development and the remedial measures being taken to lessen this leakage drainage of the sub reservoir caverns through leakage along fractures can lead to loss of hydrostatic support for the developing sub reservoir caverns and their consequent collapse furthermore rapid changes in subterranean water levels would lead to rock shattering hammer effects particularly during rapid rises in water level

quantitative determination of stress by inversion of speckle interferometer fringe patterns experimental laboratory tests summary quantitative determination of crustal stress states remains problematic here we provide a synopsis of work that is leading towards the development of an optical interferometric method that may be applied in boreholes the major obstacle to the continued development of this technique has been the problem of determining the state of stress within a stressed continuum we demonstrate the solution of both the technical and analytical issues in this contribution specifically dual beam digital electronic speckle interferometry is used to record the stressrelief displacements induced by the drilling of blind holes into blocks subject to uniaxial compressive stresses speckle interferograms are produced at rates near 4 hz using a local pearson s correlation method and are stored for analysis this time lapse capability is useful when transient effects such as thermal expansion displacements produced by the heat of drilling or ongoing time dependent deformation are active four acrylic blocks subject to uniaxial compressions from 3 8 to 5 5 mpa with the compressions oriented at different angles with respect to the axes of the interferometry system were studied relative fringe phase information was extracted from appropriate interferograms and inverted to provide a quantitative measure of the 2 d stress field within the block in general the largest value of the stress obtained in the inversion agreed with the known stress to better than 70 per cent these measurements suggest the levels of uncertainty that might be expected by use of such optical interferometric techniques this technique may show promise for quantitative stress determination in the earth to complement existing techniques as well while the interferometric principles are not exactly the same as for the popular satellite based insar techniques the optical method here has the potential to be useful in analogue physical model laboratory studies of deformation in complex structures

morphological and sedimentary features of oblique zibars in the kumtagh desert of northwestern china abstract zibars are coarse grain armored low relief aeolian bedforms with a large spacing but without slipfaces little is known of their morphodynamic processes even though they are ubiquitous at upwind desert margins in this paper we describe the morphological and sedimentary features of oblique zibars in the northeastern kumtagh desert of china analyze the effective wind regime and discuss the significance of the coarse grained sediments for zibar morphology and sedimentary structures due to a mantle of coarse grains oblique zibars and nearby linear dunes respond to different effective wind regimes that result in the angle between their geomorphological trends topographic surveys showed that the spacing of the oblique zibars ranged between 130 5 and 357 5 m and that the height ranged between 0 6 and 3 0 m the oblique zibar surface is almost entirely covered by coarse sand and includes gravel with a particle diameter of up to 2 34 the poorly sorted positively to very positively skewed surface sediments with mean grain size ranging between 0 2 and 1 5 were characterized by a bimodal distribution the spacing between the oblique zibars is closely related to the coarsest 5th percentile of the surface sediments and can potentially be explained by a combination of the saturation length and minimum dune size theories in addition the protectionist theory combined with the surface creep and vibration of coarse grains which allows infiltration of finer materials between the grains may account for the alternating coarse and fine laminae in the oblique zibars

the effect of wind and precipitation on vegetation and biogenic crust covers in the sde hallamish sand dunes vegetation and biogenic crust covers play an important role in sand dune stabilization yet there is a lack of high temporal and spatial resolution data on sand dune cover a field experiment aimed at measuring the dynamics of biogenic crust and vegetation in sand dunes was conducted at the sde hallamish sand dunes in the northwestern negev desert israel from july 2008 to august 2010 the climate of the sde hallamish sand dunes is arid the mean annual precipitation over the past 13 years is 61 mm and the dunes are linear and partially stable mainly due to the presence of biogenic crust and partially due to the presence of vegetation in july 2008 10 10 m plots on the four dune habitats crest interdune north slope and south slope were treated as follows i removal of vegetation and biogenic crust ii removal of biogenic crust only iii removal of vegetation only iv partial removal of biogenic crust and vegetation and v control plot the surface coverage of sand biogenic crust and vegetation was monitored on a monthly basis using a remote sensing technique especially developed for the sde hallamish sand dunes it was found that strong wind events with durations of several days accounted for the coverage changes in biogenic crust and vegetation the response to precipitation was much slower in addition no rehabilitation of biogenic crust and vegetation was observed within the experiment time period the changes in biogenic crust cover were not necessarily related to changes in dune dynamics since often an increase in biogenic crust cover is a result of wind erosion that exposes old crust that was buried under the sand wind hardly erodes biogenic crust at all due to its high durability to wind action the sde hallamish dunes seem to have become more active as a result of a prolonged drought during the past several years the field experiment reported here indicates that biogenic crust cover exhibits large seasonal variations that are not necessarily related to the growth of new crust but rather to the exposure of old buried crust

deformation of the central andes 15 27 s derived from a flow model of subduction zones a simple viscous flow model of a subduction zone is used to calculate the deformation within continental lithosphere above a subducting slab our formulation accounts for two forces that dominate the deformation in the overriding lithosphere tectonic forces and buoyancy forces the tectonic forces arise from the subduction of oceanic lithosphere and produce minor extension in the lithosphere near the trench and compression farther inland buoyancy forces can induce horizontal pressure gradients due to variations in crustal thickness which cause lithospheric extension where the crust is thick numerical solutions obtained by using a finite element technique are compared with observations from the central andes 15 27 s the model predicts the observed deformation pattern of extension in the forearc compression in the western monocline corresponding to magmatic activity extension in the altiplano compression in the eastern monocline and subandes and no deformation in the brazilian shield by comparing the calculated solutions with the large scale tectonic observations we are able to evaluate the forces that govern the deformation in the central andes the approximately constant subduction velocity in the past 26 m y suggests that the rate of crustal shortening in the andes has decreased with time due to the thickening of the crust

arc stresses determined by slabs implications for mechanisms of back arc spreading there is an anti correlation in stress field between the back arc area and the shallow portion of the slab generally slabs showing down dip compression have tensional back arcs and the reverse we explain this anti correlation by a force balance in the fore arc wedge between the slab pull collision force in the upper plate and the ridge push back arc spreading can occur as a passive response to the down dip compressional slab the mariana kyushu and aegean arcs are the exceptions to the anti correlation in these arcs the back arc is tensional although the slab is in down dip tension this may be because the fore arc is driven by the mantle drag toward the trench resulting in compression balanced with the slab pull the flow in the mantle would cause back arc spreading in this case

lithospheric stress strain and displacement changes from grace fo time variable gravity case study for sar e pol zahab earthquake 2018 temporal variations in the earth s gravity field can be used for monitoring of lithospheric deformations the network of continuously operating gravity stations is required for this purpose but a global coverage by such network is currently extremely sparse temporal variations in long wavelength part of the earth s gravity field have been however observed by two satellite missions namely the gravity recovery and climate experiment grace and the grace follow on grace fo these satellite gravity observations can be used to study long wavelength deformations of the lithosphere consequently considering the lithosphere as a spherical elastic shell and solving the partial differential equation of elasticity for it the stress strain and displacement inside the lithosphere can be estimated the lower boundary of this shell is assumed to be stressed by mantle convection which has a direct relation to the earth s gravity field according to runcorn s theory changes in gravity field lead to changes in the sub lithospheric stress and the stress propagated throughout the lithosphere in this study we develop mathematical models in spherical coordinates for describing the stress propagation from the sub lithosphere through the lithosphere we then organise a system of observation equations for finding a special solution to the boundary value problem of elasticity in the way that provides a stable solution in contrast models presented in previously published studies are ill posed furthermore we use constants of the solution determined from the boundary stresses to determine the strain and displacements leading to these stresses while in previous studies only the stress has been considered according to rheological properties of the lithosphere we demonstrate a practical applicability of this theoretical model to estimate the stress strain redistribution caused by the sar e pol zahab 2018 earthquake in iran by using the grace fo monthly solutions

mantle plume heads and the initiation of plate tectonic reorganizations we present results of numerical simulations which examine the plausibility of a reorganization of plate motions brought about by the interaction of a hot low viscosity plume head with the underside of a tectonic plate a numerical model of highly viscous fluid flow driven by thermal buoyancy is employed to examine the interaction of mantle plumes with surface plates in a two dimensional cartesian geometry plate like boundary conditions applied to the upper surface consist of a large active plate with fixed speed plus a smaller passive plate whose speed and direction of motion are permitted to react to tractions induced by the underlying mantle flow driven by the active plate the passive plate is also subject to applied end loads intended to simulate incipient subduction the mantle plume is initiated with a hot patch on the lower boundary and viscosity varies with temperature following an arrhenius rheology the calculations performed with fixed aspect ratio 4 1 and fixed rayleigh number ra 106 where ra refers to the strength of the starting plume were found to depend on three parameters the strength of the viscosity variation the size of the applied end load and the speed of the active plate these calculations indicate that plate motions can be sharply influenced by the lubricating effects of mantle plume heads even to the point of causing a reversal in the direction of plate motion

an integrated hydrogeological approach to evaluate the leakage potential from a complex and fractured karst aquifer example of abolabbas dam iran the design and construction of dams are risky in karst regions with active tectonic settings and strong heterogeneity due to their leakage potential hydrogeological characterization by karst specific methods can be used to reduce the risk of improper dam construction numerous karstic dams have been constructed in the world in simple tectonic settings in this study a combination of geological and hydrogeological investigations is used with extensive data collection to evaluate the leakage potential of the abolabbas dam construction project at the malagha karst aquifer a tectonized highland karst region in the southwest of iran two thrust faults which bounded the malagha karst aquifer overthrusting caused extensive crushed zones continuous lengths with high permeabilities in most of the boreholes extensive open joints and small size solution cavities the results of artificial tracer tests imply that the flow regime is diffuse the flat water table diffuse flow regime extensive crushed zones and continuous high permeabilities most probably imply that the groundwater flows through an extensive network of joints without main conduits to drain the system despite a diffuse flow regime an extensive grout curtain both in length and depth is required to prevent leakage because the loose materials of the crushed zones will be washed out without it under high hydraulic gradients after dam impoundment the impermeable formation is too deep due to overthrusting therefore a huge leakage may occur under the hanging grout curtain the results allow a clearer understanding of the location and properties of fracture zones erodible materials high permeability zones groundwater flow regime and zones of preferential flow which are essential for reducing the failure of dam construction in such environments overall it is demonstrated that integrating different complementary methods can help to minimize the uncertainties inherent in engineering problems in similar karst scarce data regions

the role of maximum wind speed in sand transporting events abstract a sand transporting event is the minimum unit of aeolian sand transport process to understand the role of maximum wind speed in such sand transporting events wind speeds were measured at a height of 2 m above the ground in the arid menggen and semi arid taibus banner regions in north china during 2009 and 2011 the sand transport flux of each sand transporting event was calculated based on theoretical equations then the relationships between the maximum wind speed and the average wind speed the duration and sand transport flux of sand transporting events were analyzed it was found that the maximum wind speed was proportional to the average wind speed of sand transporting events with a linear model fit and was also significantly correlated with the duration of sand transporting events with a power model fit the maximum wind speed was also positively correlated with sand transport flux of sand transporting events according to a power model the maximum wind speed could therefore represent both wind speed and the duration of sand transporting events and play a decisive role in the sand transport process of these events the sand transport flux of sand transporting events can be predicted rapidly and conveniently by monitoring maximum wind speed