strain patterns decollement and incipient sagducted greenstone terrains in the archaean dharwar craton south india the archaean dharwar craton is characterized by two greenstone successions the 3 ga sargur group and the 3 0 2 5 ga dharwar supergroup examples of both successions are described from the region of jayachamarajapura where they are also distinguished by different tectonic patterns the younger greenstones have undergone only minor deformation and are only slightly metamorphosed and so provide a good case study of the relative behavior of greenstones in relation to their granite gneiss country rocks a detailed structural analysis indicates two strain fields associated with two deformational episodes d1 and d2 the d1 episode produced dome and basin structures and affected merely the older greenstones and the gneisses the mapped strain field is compatible with the hypothesis that it is associated with the development of diapiric type gravitational instabilities the d2 episode affects only the younger greenstone belt which has the overall geometry of a complex syncline it is discordant over a complex of gneisses and older greenstones that was deformed during the d1 episode the base of the discordant cover sequence is tectonized and constitutes a decollement surface kinematic criteria at this surface have opposite sense and converge towards the belt axis these structural features are interpreted in terms of progressive deformation compatible with the incipient development of a sagducting trough these results are consistent with those obtained from other parts of the craton where the tectonic evolution appears to reflect mainly relative vertical displacements facilitated by the reheating of continental crust during two major archaean tectonometamorphic episodes copyright 1996 elsevier science ltd

impact of halite dissolution subsidence on quaternary fluvial terrace development case study of the huerva river ebro basin ne spain abstract this paper analyses the control of evaporite dissolution subsidence on the evolution of the lower 30 km long reach of the huerva river up to its confluence with the ebro river in the study area the huerva river flows across different interfingered lithofacies of the subhorizontally lying ebro basin fill 1 shales and sandstones upstream of cadrete 2 evaporites dominated by gypsum between cadrete and cuarte 3 gypsum with glauberite and halite units in the subsurface downstream of cuarte the halite shows a marked downvalley increase in thickness twelve terrace levels and seven pediment levels correlative to some of the terraces have been mapped in the studied area upstream of cadrete the terrace deposits with a relatively constant thickness less than 4 m and overlying unsoluble bedrock remain undeformed between cadrete and cuarte the deposits of some terraces show local thickening 60 m thick terrace alluvium that fills a 5 km long trough generated by synsedimentary subsidence phenomena caused primarily by the interstratal dissolution of halite the older terraces t1 to t4 show slight thickening 18 m and locally truncate paleocollapse structures ascribed to the interstratal karstification of halite beds the intermediate terraces t5 to t7 correspond to degradation surfaces that grade downstream of cuarte into aggradation flights underlain by the abruptly thickened deposits that fill this 5 km long dissolution trough subsidence migrated episodically downstream during the generation of these terraces and the subsidence aggradation rate was probably large enough to induce a base level drop and knickpoint migration upstream generating strath terraces with convergent longitudinal profiles the sedimentological changes that show the thickened terrace deposits in the subsidence area high proportion of overbank fines 60 including palustrine facies gravel channels with lower width depth ratio multiple fining upward cycles decrease in the calibre of the channel gravels indicate a change in the channel pattern from braided to meandering due to the lowering of the valley slope in the reach affected by subsidence some of the anomalous features of the lower terraces t8 to t12 attributable to dissolution subsidence include 1 steepening of the t8 terrace profile 2 change of the t10 terrace from degradational to aggradational downstream cuarte and 3 thickening recorded beneath the t11 terrace surface

the dead sea sinkhole hazard geophysical assessment of salt dissolution and collapse abstract a geophysical approach is presented for analyzing processes of subsurface salt dissolution and associated sinkhole hazard along the dead sea the implemented methods include seismic refraction srfr transient electromagnetic method tem electric resistivity tomography ert and ground penetration radar gpr the combination of these methods allows the delineation of the salt layer boundaries estimating its porosity distribution finding cavities within the salt layer and identifying deformations in the overlying sediments this approach is shown to be useful for anticipating the occurrence of specific sinkholes as demonstrated on both shores of the dead sea these sinkholes are observed mainly along the edge of a salt layer deposited during the latest pleistocene when lake lisan receded to later become the dead sea this salt layer is dissolved by aggressive water flowing from adjacent and underlying aquifers which drain to the dead sea sinkhole formation is accelerating today due to the rapid fall of the dead sea levels during the last 30 years caused by anthropogenic use of its water

a sinkhole susceptibility zonation based on paleokarst analysis along a stretch of the madrid barcelona high speed railway built over gypsum and salt bearing evaporites ne spain abstract this paper presents a methodology for producing sinkhole susceptibility zonations along linear infrastructures based on the analysis of the subsidence and dissolution features exposed in the adjacent cuttings and the distribution of karstic depressions the proposed approach have been applied to a 24 km long stretch of the high speed madrid barcelona railway built on halite and glauberite bearing evaporites of the tertiary zaragoza gypsum formation more than 100 km of this railway line have been built over salt bearing tertiary evaporites and trains run at a cruising speed of 300 km h the susceptibility assessment has been restricted to the sections located in karstic depressions 2 98 km and trenches excavated in the ground 13 93 km a low susceptibility has been assigned to the sections built on thickened alluvium of the huerva fluvial system 0 5 km and those in which the evaporites exposed in the cuttings do not show evidence of dissolution or subsidence 3 52 km a total of 4 5 km have received an intermediate susceptibility the cuttings in these sections show sagging structures cavities above the railway roadbed irregular rockhead or shallow alluvium bedrock boundary a high susceptibility has been assigned to a total of 6 59 km these correspond to cavities and collapse structures that reach the railway roadbed 3 61 km and karstic depressions generated by interstratal karstification and subsidence 2 98 km the paleokarst and geomorphic evidence in these sections reveals that cavities either air or sediment filled do exist beneath the railway the distribution of the karst features and susceptibility zones seems to be controlled to a large extent by the lithostratigraphy of the bedrock wedging out of the evaporites to the se and increase in the proportion of halite and glauberite to the nw the proposed zonation could be used as the basis for the selection of the stretches where further investigations and the application of mitigation measures would have a better cost benefit ratio

modelling stress dependent permeability in fractured rock including effects of propagating and bending fractures the influence of in situ stresses on flow processes in fractured rock is investigated using a novel modelling approach the combined finite discrete element method femdem is used to model the deformation of a fractured rock mass the fracture wall displacements and aperture changes are modelled in response to uniaxial and biaxial stress states the resultant changes in flow properties of the rock mass are investigated using the complex systems modelling platform csmp csmp is used to model single phase flow through fractures with variable aperture and a permeable rock matrix the study is based on a geological outcrop mapping of a low density fracture pattern that includes the realism of intersections bends and segmented features by applying far field boundary stresses to a square region geologically important phenomena are modelled including fracture dependent stress heterogeneity the re activation of pre existing fractures i e opening closing and shearing the propagation of new fractures and the development of fault zones flow anisotropy is investigated under various applied stresses and matrix permeabilities in situ stress conditions that encourage a closing of fractures together with a more pervasive matrix dominated flow are identified these are compared with conditions supporting more localised flow where fractures are prone to dilatational shearing and can be more easily exploited by fluids the natural fracture geometries modelled in this work are not perfectly straight promoting fracture segments that dilate as they shear we have demonstrated the introduction of several realistic processes that have an influence on natural systems fractures can propagate with wing cracks there is the potential for new fractures to connect with existing fractures thus increasing the connectivity and flow blocks can rotate when bounded by fractures bent fractures lead to locally different aperture development highly heterogeneous stress distributions emerge naturally results presented in this work provide a mechanically rigorous demonstration that a change in the stress state can cause reactivation of pre existing fractures and channelling of flow in critically stressed fractures

management and mitigation of sinkholes on karst lands an overview of practical applications when karst lands are developed for residential or commercial purposes sinkholes are to be properly managed or mitigated this paper discusses various types of sinkholes and their possible formation mechanisms presents some guidelines for sinkhole management and summarizes several engineering measures for sinkhole remediation because a sinkhole is often not an isolated feature but a component of an integrated groundwater and surface water system knowledge of the sinkhole geology and hydrology is essential in selection of the proper management tools and remediation options adverse effects including flooding additional sinkholes and groundwater contamination can result from poorly managed or improperly repaired sinkholes

finite deformation in and around a fluid sphere moving through a viscous medium implications for diapiric ascent abstract different types of geodynamically active regions like mountain belts hot spots or areas of salt tectonics are characterized by diapirism one key for the reconstruction of the dynamic history of such structures is the progressive strain which can sometimes be determined from field observations successful interpretation of such observations requires a quantitative model of the finite strain in and around a rising diapir a constant viscosity fluid sphere of radius r rising through another isoviscous fluid is assumed to approximate the buoyant motion of a diapir known analytical solutions for the velocity fields are used to numerically evaluate the finite deformation in and around the sphere regions of very high strains are found in a tube with a radius 1 2 r behind the sphere and in a shell of thickness of 0 1r around the sphere the following three dimensional strain regimes can be identified in the half space above the sphere down to its equator finite strains are oblate behind the sphere they progressively change to plane strain in the diapiric source region they are prolate viscous drag at the sphere s surface leads to an internal circulation with one overturn after 10r of rise if the sphere has a relatively low viscosity finite strains within the fluid sphere show a continuous increase with superimposed cyclic straining and unstraining after several body radii of rise the strains become highly inhomogeneous inside the sphere except along the vertical axis and just inside the sphere s surface where strong prolate and oblate strains are observed respectively finite strain determinations in a falling ball experiment cruden 1988 are compared with the theoretical results at horizontal distances of a few body radii from the fall axis the effect of confining container walls is clearly seen in the experimental strain data the results are compared briefly with available strain data from the field which seem to be significantly lower than predicted proposed explanations include a short memory of the rock fabric and a lack of recognition of the strain concentration which would be expected for a temperature dependent rheology it might also be possible that few natural diapirs rise more than a few radii in the solid state

convection experiments in high prandtl number silicones part 1 rheology equipment nomograms and dynamic scaling of stress and temperature dependent convection in a centrifuge it has been impossible to model mantle convection by other than numerical methods because dynamically scaled laboratory experiments of practical size in high prandtl number fluids would require a temperature gradient reaching far above the sublimation temperature of any known fluid however convection can be established in high prandtl number fluids without large temperature gradients and length scales if the thermal buoyancy forces are enhanced by increasing the gravitational acceleration this has been realized by placing the test tank in a high speed centrifuge up to 3000 rpm at the hans ramberg tectonic laboratory uppsala the centrifugal acceleration imposes an apparent gravity field several thousand times the earth s gravity by using this method supercritical rayleigh numbers up to 106 can be achieved in a transparent polymer fluid sgm36 of prandtl number 108 the carefully developed test tank and control unit and a rigorous derivation of the conditions for dynamic similarity of convection in fluids with temperature and stress dependent rheology facilitates detailed laboratory studies of high prandtl number convection the working philosophy section 2 equipment section 3 non newtonian and temperature dependent scaling procedure section 4 and practical nomograms section 5 are presented here to aid such laboratory studies the significance of this new laboratory method for studying convection is outlined in section 6 real convection experiments in high viscosity polydimethylsiloxanes now have the potential to contribute to the understanding of six major aspects of convection these are 1 1 progressive deformation and displacement in three dimensional convective flow fields 2 2 convective mixing 3 3 convection with high prandtl numbers 4 4 non newtonian flow 5 5 temperature dependent flow and 6 6 high rayleigh number convection detailed applications will be discussed in a companion paper part 2 of the present project

urban geophysical approach to characterize the subsoil of the main square in san benedetto del tronto town italy abstract most historic urban areas have a lack information regarding subsoil and buried structures such as old utilities private cellars etc therefore when planning new engineering interventions limited information of subsoil composition leads to greater risk when conserving and reclassifying historic urban areas obtaining information about potential sources of risk for infrastructures is important for civil engineering however only high resolution information improves the management of important activities involving historic urban infrastructure although direct measurements can alleviate a lack of information concerning the subsoil they are generally expensive invasive and interferes with everyday use of the site for long periods therefore the use of low or non invasive technologies to quickly and accurately analyse the subsoil is preferable and strongly recommended for this purpose a new discipline recently termed urban geophysics is developing rapidly this paper describes an application of urban geophysics in a historically important italian town in order to characterize the subsoil and identify the presence of natural voids and unknown anthropic underground structures such as cellars an extensive geophysical investigation based on use of electrical resistivity tomography and ground penetrating radar to perform a survey in the town of san benedetto del tronto marche region italy with a total time frame of around two days was carried out previously unknown buried structures and geological discontinuities were highlighted by using these geophysical techniques in order to support and confirm the interpretation of the geophysical data geotechnical drillings were carried out finally direct data validated and supported the non invasive geophysical results the combined results have provided valuable information to the local authorities and engineers involved in the decision making process for the construction of new underground structures

a comprehensive approach to karst identification and groutability evaluation a case study of the dehou reservoir sw china abstract yunnan province in sw china has one of the most developed karst terrains in china and has been historically affected by sinkholes and other instability phenomena caused by unpredictable cavity formation and well developed underground hydraulic conduits during construction of a karst seepage control reservoir project grouting of a 4 6 km long anti seepage curtain in yunnan province some typical detection methods electromagnetic and water injection tests failed to map the complex geo structural karst zones clearly resulting in considerable grout loss and excessive leakage during the grouting phase of this project to deal with this limitation a comprehensive approach including a new drilling process monitoring system borehole electrical resistivity tomography borehole sonic logging and water injection tests is employed to identify the general characterization geometry and spatial distribution of karst zones along the anti seepage curtain additionally a deep belief network dbn model replaced the empirical relationships typically used to predict the grouting quantity for groutability evaluation in karstified areas the dbn algorithm is trained by data collected using this comprehensive approach rate of penetration rock permeability resistivity and p wave velocities and two previous grouting quantities as input data the lessons learned in this case study permit us to define an effective comprehensive approach for delineating the general characterization of karst zones between two boreholes and locations of potential conduits for grout flow through the borehole the proposed dbn model can predict the grouting quantity for karst regions and the accuracy of prediction is greatly affected by previous grouting quantity rather than the collected parameters

centrifuged models of gulf of mexico profiles abstract physical models dynamically scaled in a centrifuge are used to explore the importance of slope progradation in driving internal salt structures much further horizontally than they rise large increments of ductile plastic overburden added at normal gravity values simulated primary clastic sedimentary progradation of a clastic slope over a layer of buoyant fluid simulating salt during load increments at a nominal 800 g in a centrifuge this ductile topographic slope spread over the ductile decollement except for down to basin growth faults all the structures considered to be distinctive in the northern gulf of mexico are simulated in the models that are scaled such that 1 mm and 60 s in the model correspond to 1 1 5 km and 2 6 ma in the prototype ratios of the rate of advance to the rate of rise of the shelf break compared with the rate of advance and increase in relief of salt structures control how much of the deep autochthonous salt is squeezed ahead of the advancing shelf and the paths this salt takes to shallow structural levels the few three dimensional diapiric stocks which developed from many two dimensional mullions in the models spread stock canopies which advanced huge distances before some became tongue canopies by climbing over clastic sediments already aggraded in front of them the models emphasize the significance of ductile spreading of the clastic sediments now being discerned by backstripping

diapiric spoke patterns abstract not all finger like diapirs evolve from or into linear walls as previously supposed that would imply that all contemporaneous finger diapirs lie in rows and many do not physical models demonstrate that diapiric linear walls or rows of fingers have to be forced by lateral forces lateral boundaries or internal edge effects by contrast the kinematics of the simplest isothermal gravity overturns responsible for finger like diapirs are geometrically kinematically and dynamically similar to the spoke patterns of vigorous thermal convection this is because rayleigh taylor rt diapirism and rayleigh benard rb thermal convection are end members of a continuous dynamic spectrum due to any combination of compositional or thermally induced density inversions all simple rt overturns are dynamically similar but the vigour of thermal convection varies with the heat flow the kinematics of spoke patterns are difficult to study in rapid multiple overturns of thermal convection in low viscosity fluids however spoke patterns in slow isothermal diapiric analogues can be analysed at any stage during their single overturn such studies indicate that two sets of spokes conduct fluids of different densities horizontally along the top and bottom boundaries to finger like diapiric stems or plumes where they rise or sink to spread in polygonal bulbs at the opposite boundary spokes converge to hubs at the bottom boundary beneath stems feeding diapiric bulbs at the top boundary and vice versa if the movement cells are considered centred on rising plumes the cell corners are mapped by sinking plumes the differences between spoke patterns and previously understood diapiric patterns are illustrated by geological examples with emphasis on relevance to the search for oil and gas physical arguments suggest that spoke patterns are probably the most common geometries of gravity driven overturns in layered rocks of both the crust and the mantle

the mechanism of ascent and emplacement of granite magma during transpression a syntectonic granite paradigm we propose a model for syntectonic ascent and emplacement of granite magma based on structural relations in part of the northern appalachians in the study area in western maine strain was distributed heterogeneously during devonian acadian transpression metasedimentary rocks migmatites at high grades record two contrasting types of finite strain in zones that alternate across strike rocks in both types of zones have a penetrative moderately to steeply ne plunging mineral elongation lineation defined by bladed muscovite fibrolite sillimanite at high grades in straight belts of enhanced deformation rocks have s l fabrics that record apparent flattening to plane strain apparent flattening zones afzs but rocks between these belts have l s fabrics that record apparent constriction apparent constriction zones aczs at metamorphic grades above the contemporary solidus rocks in afzs developed stromatic structure in migmatite which suggests that percolative flow of melt occurred along the evolving flattening fabric stromatic migmatites are intruded by concordant to weakly discordant m scale composite sheet like bodies of granite to suggest magma transport in planar conduits through the afz rocks inhomogeneous migmatite is found in the intervening aczs which suggests migration of partially molten material through these zones en masse probably by melt assisted granular flow inhomogeneous migmatites are intruded by irregular m scale bodies of granite that vary from elongate to sub circular in plan view and seem cylindrical in three dimensions these bodies apparently plunge to the northeast parallel to the regional mineral elongation lineation to suggest magma transport in pipe like conduits through the acz rocks we postulate that the form of magma ascent conduits was deformation controlled and was governed by the contemporaneous strain partitioning magma ascent in planar and pipe like conduits through migmatites is possible because oblique translation during contraction displaces isotherms upward in the orogenic crust to form a thermal antiform within this hot corridor it is the difference in temperature between melt producing reactions in the anatectic zone and the wet solidus for granite melt that enables magma to migrate pervasively up through the orogenic crust without congealing heat advected with the migrating melt promotes amplification of the thermal antiform in a feedback relation that extends the zone of plastic deformation and pervasive melt migration to shallower levels in the crust at the wet solidus we suggest melt flows obliquely toward axial culminations in the thermal antiform which are sites of melt accumulation and perturbations from which magma may escape to form plutons batches of melt that escape from these perturbations may be trapped by tectonic structures higher in the crust or ascent may become inhibited with decreasing depth by thermal arrest and solidification if the rate of arrival of subsequent melt batches exceeds the rate of crystallization at the site of pluton construction melt pressure ultimately may lead to sub horizontal magma fracture or viscous flow of wall rocks may allow lateral spreading the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduit as the thermal antiform decays the height of sub solidus crust that separates the deepest part of the pluton from the anatectic zone increases consequently pluton inflation declines and solidification leads to infilling of the magma feeder channel to form a root zone that passes downward into migmatite which may explain the difficulty of determining precisely the floor to these deeper segments of large plutons using gravimetry

coupled crust mantle dynamics and intraplate tectonics two dimensional numerical and three dimensional analogue modeling 1 tectonic deformation of some intraplate regions may be caused by the rayleigh taylor rt instability of dense subcrustal lithosphere mantle lithosphere as it descends into the mantle we report on a series of scaled three dimensional 3 d analogue and 2 d numerical experiments of coupled crust mantle dynamics that study such a process the models investigate the effects of two geometries of rt instability linear versus axisymmetric and use different rheological stratifications of the crust the growth of the rt instability is strongly influenced by crustal rheology while rt growth rates are not greatly influenced by the geometry of the mantle lithosphere instability itself the surface is experiments having a viscous only crust are characterized by significant crustal contraction and thickening above the mantle downwelling and extension and thinning in adjacent regions in experiments with a brittle upper crust the surface deformation is much more subdued however strong mantle flow induced deformation still occurs in the ductile lower crust beneath the quiescent brittle upper crust when the lower crust is relatively strong localized styles of extensional and contractional structure develop in the brittle upper crust owing to the greater degree of coupling between upper crust and the mantle instability in all the experiments a portion of the ductile lower crustal material is entrained within the downgoing rt instability deep into the mantle the interplay between dynamic topography and crustal thickening thinning induced by the underlying mantle flow governs various time dependent phases of subsidence and uplift of the model surface the experiments help to account for a number of first order tectonic behaviors of the lithospheres of earth and other terrestrial planets for example intraplate orogens and basins complex localized tectonic structure in intraplate settings and deep crustal seismic fabrics may arise as the variable crustal response to underlying mantle lithosphere rt instabilities

forward and reverse modeling of the three dimensional viscous rayleigh taylor instability a combined nite dierence spectral method is used to model the 3d viscous rayleigh taylor instability numerically calculated growth rate spectra are presented for an initial sinusoidal perturbation of the interface sep arating two fluids with amplitude 10 3 h and 0 2h w here h is the height of the system at small initial amplitude growth rate spectra closely follow linear theory whereas the calculation with higher initial amplitude shows wavelength selection towards 3d perturbations numerical simulations and analytical theory are used to evaluate the applicability of previous 2d numerical models which is shown to depend on 1 the wavelength and amplitude of an initially 2d si nusoidal perturbation and 2 the amplitude of background noise it is also shown that reverse backward modeling is capableofrestoringtheinitialgeometryaslongasoverhangs are not developed if overhangs are present the possibility ofrestoringtheinitialconditionsislargely dependentonthe stage of overhang development

small scale instabilities below the cooling oceanic lithosphere summary interpretation of satellite altimetry data as well as ship bathymetry data revealed strongly elongated anomalies roughly perpendicular to the mid ocean ridges in the indian and east pacific oceans a spectral analysis of gravity altimetry data along profiles parallel to the east pacific rise indicated wavelengths of about 150 180 km close to the ridge and about 250 km further away a simple model of rayleigh taylor instabilities developing at the base of the cooling lithosphere is discussed and applied to the data by considering thermal divusion and comparing rayleigh taylor growth rates to the velocity of the thermal front in the cooling lithosphere we are able to explain the observed anomalies by instabilities developing below the lithosphere in a layer with a viscosity of about 1019 pa s above an asthenospheric layer with a viscosity reduction of 2 3 orders of magnitude

influence of pre existing salt diapirs on 3d folding patterns abstract the 3d detachment folding instability gives rise to a wide variety of fold shapes e g from dome shape structures to long en echelon or straight anticlines as a result of interactions between growing fold segments the 3d growth of these folds as well as the wavelength and lateral propagation of folds is controlled by the physical parameters of a detachment layer and its overburden however the existence of initial heterogeneities such as pre existing salt plugs within the sedimentary cover might affect fold development as well we use numerical modeling to investigate how the fold pattern is affected by pre existing salt structures high resolution 3d folding simulations with and without pre existing salt structures were performed in which we varied the shape height and spacing of pre existing diapirs in a first geometric setup we employed a multilayer setup and synthetic diapir distributions in order to study the influence of diapir spacing on fold spacing and patterns in a second geometric setup we use a diapir distribution that fits the observed exposed diapir distribution in the southeastern zagros results show that the presence of diapirs does not considerably change the wavelength of the folds which is in all cases close to the dominant folding wavelength that develops in the absence of diapirs yet the presence of pre existing structures speeds up the folding instability in those locations and also affects folding patterns as the diapirs localize the initial deformation by accommodating folding above them which results in the diapirs being located in the core of the folds if diapir spacing is much smaller than the dominant folding wavelength diapirs are located in different structural positions such as fold synclines or flanks

numerical study of critical behaviour of deformation and permeability of fractured rock masses abstract the connectivity of fractures in rock masses is determined using a numerical simulation method there is a continuous fracture cluster throughout a fractured rock mass if fracture density d is at or above a threshold fracture density d c fractal dimension d f is used to describe the connectivity and compactness of the largest fracture clusters d f increases with increasing fracture density percolation theory is used to determine the universal law d f a f d d c f which describes the critical behaviour of connectivity of fractures in rock masses the results from numerical modeling show that the deformability of fractured rock masses increases greatly with increasing fracture density i e fractal dimension and the critical behaviour of deformability can be described by b s a d d f s also the overall permeability of a fractured rock mass occurs at or above a critical fracture density d c and increases with increasing fracture density the critical behaviour of permeability can be described by q a p d d c p the critical behaviour of connectivity and permeability of naturally fractured rock masses is examined using the universal forms

stress constraints and hydrofracturing stress data for the continental crust faulting and seismicity in the upper continental crust require considerable differential stresses application of experimentally developed friction fracture and flow laws shows that high differential stresses can only exist in the uppermost crust direct hydraulic fracturing measurements in deep boreholes seem to support this rock mechanics conclusion the experimental data base presently consists of approximately 500 hydrofrac tests conducted in about 100 boreholes at about 30 different geographical locations to illustrate the variation of measured stresses with depth the data are expressed as dimensionless horizontal stresses in the forms h h sv z wheres v gz extrapolation of the experimental data to greater depth shows that the minor horizontal stress approaches the values h sv 0 5 which limits friction on wet faults and that the major horizontal stress approaches a value close tos h sv 1 at rather shallow depth 5 to 10 km this limits faulting and seismicity in most of the upper crust to either strike slip or normal faults the lower boundary for seismicity is mainly dependent on tectonic strain accumulation and rock creep at the environmental conditions at depth

strain patterns in archaean dome and basin structures the dharwar craton karnataka south india abstract models simulating the role of gravity in the earth s crust are the main source of criteria used for the field identification of diapirs after a short review of the distribution of finite strain in experimental diapir models we describe an example where differential erosion of a tilted craton has provided 3d geometrical information on patterns in a diapiric system at various depths from greenschist to granulitic facies conditions within the archaean continental crust of the dharwar craton south india diapirs and anti diapirs sagducted greenstones are observed at different levels structures and strain are consistent with all the field identification criteria inferred from experimental simulation but some peculiar structural features are also observed which are not predicted by the models these features such as strain trajectory triple junctions result from i the progressive deformation of diapiric domes or sagducted basins ii interferences between diapiric structures body forces and iii the superimposition of diapiric strain fields on regional horizontal shortening boundary forces

glauberite halite association of the zaragoza gypsum formation lower miocene ebro basin ne spain glauberite is the most common mineral in the ancient sodium sulphate deposits in the mediterranean region although its origin primary or diagenetic continues to be a matter of debate a number of glauberite deposits of oligocene miocene age in spain display facies characteristics of sedimentologic significance in particular those in which a glauberite halite association is predominant in this context a log study of four boreholes in the zaragoza gypsum formation lower miocene ebro basin ne spain was carried out two glauberite halite lithofacies associations a and b are distinguished association a is composed of bedded cloudy halite and minor amounts of massive and clastic glauberite association b is made up of laminated to thin bedded clear macrocrystalline massive clastic and contorted lithofacies of glauberite and small amounts of bedded cloudy halite transparent glauberite cemented by clear halite as well as normal graded and reverse graded glauberite textures are common this type of transparent glauberite is interpreted as a primary subaqueous precipitate gypsum thenardite or mirabilite are absent in the two associations the depositional environment is interpreted as a shallow perennial saline lake system in which chloride brines association a and sulphate chloride brines association b are developed the geochemical study of halite crystals bromine contents and fluid inclusion compositions demonstrates that conditions for co precipitation of halite and glauberite or for precipitation of na sulphates mirabilite thenardite were never fulfilled in the saline lake system

paleoflood records from sinkholes using an example from the ebro river floodplain northeastern spain 53 pags 10 figs the definitive version is available at https www cambridge org core journals quaternary research

anatomy of mushroom shaped diapirs we produced more than 100 mushroom shaped diapirs in eight centrifuged models under acceleration of 1200 g the modelling results allow natural examples to be recognized mushroom diapirs have an overhanging bulb fringed by one or more skirts which can curl inward to form vortices capable of entraining cover material to various degrees most of the internal folds are downward facing the oldest buoyant unit occurs in the skirt and in the diapiric core younger buoyant units or their immediate cover are infolded in crescentic patterns external mushroom diapirs have skirts that infold cover material with greater maturity the skirts can curl inward to form an external vortex entraining cover in contrast internal mushroom diapirs have skirts confined entirely within the intrusion again with greater maturity these confined skirts may curl inward but they entrain only diapiric material internal mushroom structure results from toroidal circulation confined within the diapir where isoviscosity prevails external mushroom structure results where source and entrained cover have similar effective viscosities entrained inclusions of more permeable country rock threaten the integrity of a mined cavern by creating a plumbing system

a case of man induced ground subsidence and building settlement related to karstified gypsum oviedo nw spain this paper presents the research carried out to shed light on a sudden settlement and its consequences that occurred in the city of oviedo ground subsidence in the ventanielles area led to severe damage and the subsequent demolition of two buildings with 362 flats resulting in losses of 18 million euros the investigation allowed the identification of a buried sinkhole filled with up to 13 m of fluvial sediments linked to the dissolution of a paleogene gypsum unit with a maximum thickness of 18 m and containing metre sized cavities the triggering process that reactivated the paleosinkhole was found to be the pumping of water from a confined aquifer related to excavation work during the construction of a nearby underground parking lot this extraction modified the natural hydrological regime the compaction and migration of alluvial sand towards the karstic cavities were the main subsidence mechanisms responsible for the structural damage aggravated by the poor quality of the buildings and the geotechnical behaviour of the supporting ground

late holocene episodic displacement on fault scarps related to interstratal dissolution of evaporites teruel neogene graben ne spain abstract the mio pliocene formations of the turolian type section teruel graben spain have sagged due to dissolution of the underlying triassic evaporites generating a 1 7 km long monocline and accompanying synform with 130 m of structural relief the crest of the monocline is affected by a graben that counterbalances the shortening caused by passive bending in the adjacent syncline this graben is controlled by a master synthetic fault and a swarm of antithetic and synthetic faults with a conspicuous geomorphic expression after acquiring ground penetrating radar gpr profiles three trenches were excavated in depressions associated with uphill facing fault scarps to our knowledge these are the first trenches excavated across faults caused by deep seated dissolution of evaporites the geometrical relationships observed in two trenches indicate late holocene episodic displacement as many as 3 events some of the parameters estimated for the investigated faults are clearly different from those expectable for tectonic faults in this intraplate area they include high apparent vertical slip rates 0 6 1 mm yr low average recurrence of faulting events 1 2 2 ka and very high displacement per event values 65 cm for surface ruptures less then 200 m long our findings suggest that considering evaporite collapse faults as creeping structures is not a reliable criterion to differentiate between tectonic faults seismogenic and dissolution induced gravitational faults nonseismogenic

investigation of a large collapse sinkhole affecting a multi storey building by means of geophysics and the trenching technique zaragoza city ne spain an active sinkhole around 100 m long has been investigated in the city of zaragoza ne spain subsidence activity on this depression including the sudden occurrence of a collapse sinkhole 5 m across led to the abandonment of a factory in the 1990s at the present time a building with 100 flats and shallow pad foundations partially built on the sinkhole is affected by rapid differential settlement the development of the sinkhole results from the karstification of the halite and glauberite bearing bedrock and the sagging and collapse of the overlying bedrock and alluvium more than 30 m thick gpr and electrical resistivity profiles have provided information on the distribution and geometry of the subsidence structure the application of the trenching technique and geochronological methods ams and osl dating has allowed us to infer objective and practical data on the sinkhole including 1 limits of the subsidence structure 2 subsidence mechanisms 3 cumulative subsidence 408 cm 4 subsidence rates on specific failure planes 1 8 cm year 5 episodic displacement regime of some fault planes the available information indicates that the progressive deformation recorded in the building will continue and might be punctuated by events of more rapid displacement this work illustrates the practicality of the trenching technique for the study of sinkholes in mantled karst areas

technology and geomorphology are improvements in data collection techniques transforming geomorphic science in recent years technological developments have revolutionized our ability to collect data in geomorphology enhanced data collection not only enables us to provide deeper answers to a wider range of fundamental questions about the earth s surface but also encourages us to pose new questions this paper considers in more detail the relationships between science technology and the development of geomorphological tools and techniques reviews the spectrum of tools and techniques now available to geomorphologists and critically assesses what impact new technologies are having on geomorphology it focuses on the role of technology in biogeomorphology and weathering research and how it is advancing theoretical empirical and applied dimensions of these growing sub fields of geomorphology five areas of important technological development are reviewed remote sensing dating geophysical techniques field and laboratory based analysis and sensing of physical and chemical characteristics and field and laboratory based analysis of biological properties there is good evidence that taken together technological developments are revolutionizing geomorphology through opening the doors to better cross scalar investigations blurring the boundaries between laboratory field and computer model and facilitating cross disciplinary and democratized research

palaeoproterozoic intraplating exposed by resultant gravity overturn near kiruna northern sweden abstract the tectonic history of the kiruna area is reexamined on the basis of four newly available digitised geophysical maps a literature survey and some first hand field observations a basement complex of archaean gneisses was unconformably overlain by a palaeoproterozoic sequence of metabasalt andesite and keratophyric porphyries with interstratified tuffs and sediments the cover was then detached from its basement by an orogeny with a northerly tectonic grain a pile of ductile nappes separated by mylonites in the east pushed westward an imbricate fold thrust belt that may have decoupled over an evaporite unit of regional extent conglomerates and quartzites accumulated in a foredeep migrating in front of a wedge of emergent thrusts the allochthonous cover then developed a vertical north trending foliation in high t low p conditions as it foundered among buoyant diapirs of remobilised granitoid basement the near constant lateral spacing of the centres of these diapirs their mushroom shapes and the absence of contemporaneous volcanic rocks suggest that these diapirs rose in the solid state the region continued to distort episodically even after diapir emplacement ductile shear zones evolved through vein systems to faults as the region cooled and was uplifted before the cambrian the youngest fault movements clearly displace 9000 years old glacial deposits post or late orogenic plutons in the kiruna area appear to be contemporaneous with syn svecofennian plutons further south we therefore suggest reinstating the label svecokarelian for the orogeny in the kiruna area heat advected by melts from the mantle is invoked to account for the archaean basement risking in two convective stages the first as porphyritic lavas the second as solid state diapirs melts rose rapidly and erupted before the svecokarelian orogeny while the slower diapirs ended it we attribute the current southwestern dip of the diapir zone to extension of svecokarelian crust before the svecofennian magmatic arc was built above it

subsidence rates and urban damages in alluvial dolines of the central ebro basin ne spain in the central ebro basin alluvial dolines develop on quaternary materials overlying neogene evaporites this process is very active analysing aerial photographs of different years important differences can be observed since the 1970s when the urbanisation of the area took place karst processes have damaged many buildings and infrastructures from the dates of construction and the repair of a number of buildings and pavements we calculate subsidence rates 12 120 mm year moreover we decided to monitor for around 4 years three dolines developed on urban areas to determine their subsidence behaviour a water level device with an error of 2 3 mm was utilised for this purpose the subsidence rates so obtained are 64 5 39 and 21 mm year which fit with the previous data from repaired zones

paleosubsidence and active subsidence due to evaporite dissolution in the zaragoza area huerva river valley ne spain processes spatial distribution and protection measures for transport routes abstract the lowest 17 km long reach of the huerva river valley down to its confluence with the ebro river in zaragoza city flows across salt bearing evaporites of the ebro tertiary basin ne spain upstream the horizontally lying miocene evaporites are interfingered with non soluble distal alluvial fan facies shales and sandstones the proportion of soluble facies in the huerva river valley increases in a downstream direction towards the basin depocenter on the basis of the type and magnitude of the paleosubsidence features the valley has been divided into four reaches along reach i undeformed terrace deposits less than 4 m thick rest on insoluble detrital bedrock in reaches ii and iii dissolution at the alluvium bedrock boundary has generated local thickening deformation and paleocollapse structures which only affect the alluvial mantle in reach iv terrace deposits thicken to over 60 m resulting from a large scale synsedimentary subsidence in this sector subsidence locally affects to both the alluvium and the underlying bedrock this indicates that dissolution acts at the rockhead beneath the alluvial cover alluvial karst and within the evaporitic substratum interstratal karst the development of an intraevaporitic karst in reach iv is attributed to gypsum and salt dissolution irregular terrace gravel bodies gravel pockets embedded in a fine grained matrix associated with paleocollapse structures have been interpreted as liquefaction fluidization structures resulting from ground acceleration and suction induced by catastrophic collapses subsidence is currently active in the region affecting areas with a thin alluvial cover in reaches iii and iv the low subsidence activity in most of zaragoza city is explained by the presence of thickened around 50 m and indurated alluvial deposits in the surrounding area numerous buildings in cadrete and santa fe villages have been severely damaged by subsidence natural and human induced subsidence favours the development of slope movements in the gypsum scarp overlooking cadrete village several transport routes including the imperial canal irrigation canal and the recently completed madrid barcelona high speed railway are affected by human induced sinkholes the paleocollapse structures exposed in the trenches of this railway and a ring road under construction point to hazardous locations underlain by cavities and collapse structures where special protection measures should be applied rigid structures are recommended beneath the high speed railway with sufficient strength to span the larger sinkholes with no deformation electronic monitoring devices linked to a warning system can detect subtle subsidence induced deformations in carriageways or railways this research demonstrates that the study of the paleokarst helps to understand the processes involved in the present day subsidence phenomena and their general spatial distribution

a detailed view of the injection induced seismicity in a natural gas reservoir in zigong southwestern sichuan basin china 1 seismicity at a gas reservoir located in the relatively stable sichuan basin china mirrors the injection pressure of unwanted water suggesting that the seismicity is injection induced injection under high pressure on a routine basis began on 9 january 2009 and continued to july 2011 during the injection period over 120 000 m3 of water was pumped under a wellhead pressure of up to 6 2 mpa into the limestone formation of permian 2 45 to 2 55 km beneath the surface the injection induced more than 7000 surface recorded earthquakes including 2 m4 the largest one was ml4 4 20 m3 and more than 100 m2 events data observed by a nearby local seismic network and five temporal stations provide a detailed view of the spatiotemporal distribution of the induced earthquakes most events were limited to depths ranging from 2 5 to 4 km which is consistent with the limestone formation of permian in a map view hypocenters are concentrated in a nnw extended ellipsoidal zone approximately 6 km long and approximately 2 km wide centered approximately at the injection well multisources of evidence such as the shear mechanism pattern of hypocenter distribution and small elevated pore pressure as compared with the least principal stress in the region show that the induced earthquakes occurred as a result of lowering of the effective normal stress on known or unknown preexisting blind faults which are critically loaded under the regional stress field epidemic type aftershock sequence modeling results indicate that injection inducing and earthquake triggering are both important during earlier periods of injection while later periods are dominated by forced injection induced seismicity

patterns of total and incremental strain in subsiding troughs experimental centrifuged models of inter diapir synclines the experimental technique of centrifuge modelling has been used to elucidate patterns of total strain and progressive deformation associated with troughs that form by gravitational subsidence of a dense cover into a less dense basement model structures are analogous to synclines found between mantled gneiss domes and the models provide data with which to test the hypothesis that archean greenstone belts are products of vertical gravity tectonics experimental results include the following 1 strain within the main body of subsiding belts is dominated by strong horizontal contraction and vertical extension in natural structures this strain pattern would produce vertical foliation and steeply plunging mineral lineation 2 within cover units near trough margins the flattening plane trends parallel with or at a low angle to the cover basement interface at all levels in the trough 3 patterns of strain within subsiding troughs at least as expressed in surface deformation reflect the geometry of the

application of geochemical and groundwater data to predict sinkhole formation in a gypsum formation in manitoba canada numerical modelling approaches were used to investigate coupled groundwater flow and reactive transport processes in gypsum karst sub terrain a regional equipotential map and steady state flow model were created using scarce data to gain insights into flow patterns and identify potential areas at risk for cavity and sinkhole development in a shallow gypsum formation coupled flow and reactive transport modelling was used to simulate the dissolution of gypsum between a sinkhole in a man made drainage ditch and a quarry where freshwater enters the drainage ditch and flows toward the quarry field data from a tracer test were used to characterize flow in the study area the resulting regional equipotential map was valuable in identifying potential areas of sinkhole development sinkholes occurred in areas underlain by thick gypsum formations with high flow gradients and radial flow the reactive transport model was valuable in identifying the growth of the cavity and the timeline for the potential risk to road infrastructure the reactive transport model indicated that cavity growth could be slowed by removing the inflow of freshwater into the drainage ditch groundwater equipotential maps flow models and reactive transport models are valuable tools for the investigation of sub terrain karst development including cavity development and sinkhole formation in evaporite minerals

a model to explain joint patterns found in ignimbrite deposits the study of fracture systems is of paramount importance for economic applications such as co2 storage in rock successions geothermal and hydrocarbon exploration and exploitation and also for a better knowledge of seismogenic fault formation understanding the origin of joints can be useful for tectonic studies and for a geotechnical characterisation of rock masses here we illustrate a joint pattern discovered in ignimbrite deposits of south america which can be confused with conjugate tectonic joint sets but which have another origin the pattern is probably common but recognisable only in plan view and before tectonic deformation obscures and overprints it key sites have been mostly studied by field surveys in bolivia and chile the pattern is represented by hundreds of meters up to kilometre long swarms of master joints which show circular to semi circular geometries and intersections that have x and y patterns inside each swarm joints are systematic rectilinear or curvilinear in plan view and as much as 900 m long in section view they are from sub vertical to vertical and do not affect the underlying deposits joints with different orientation mostly interrupt each other suggesting they have the same age this joint architecture is here interpreted as resulting from differential contraction after emplacement of the ignimbrite deposit above a complex topography the set of the joint pattern that has suitable orientation with respect to tectonic stresses may act to nucleate faults

improving sinkhole hazard models incorporating magnitude frequency relationships and nearest neighbor analysis abstract this work presents a methodology for elaborating sinkhole hazard models that incorporate the magnitude and frequency relationships of the subsidence process the proposed approach has been tested in a sector of the ebro valley mantled evaporite karst where sinkholes largely induced by irrigation practices have a very high occurrence rate 50 sinkholes km 2 yr in this area covering 10 km 2 a total of 943 new cover collapse sinkholes were inventoried in 2005 and 2006 multiple susceptibility models have been generated analyzing the statistical relationships between the 2005 sinkholes and different sets of variables including the nearest sinkhole distance the quantitative evaluation of the prediction capability of these models using the 2006 sinkhole population has allowed the identification of the method and variables that produce the most reliable predictions the incorporation of the indirect variable nearest sinkhole distance has contributed significantly to increase the quality of the models despite simplifying the modeling process by using categorical rather than continuous variables the best susceptibility model generated with the total sinkhole population and the selected method and variables has been transformed into a hazard model that provides minimum estimates of the spatial temporal probability of each pixel to be affected by sinkholes of different diameter ranges this transformation has been carried out combining two equations derived from the more complete 2006 sinkhole population one of them expressing the expected spatial temporal probability of sinkhole occurrence and the other the empirical magnitude and frequency relationships generated for two different types of land surfaces which control the strength of the surface layer and the size of the sinkholes the presented method could be applied to predict the spatial temporal probability of events with different magnitudes related to other geomorphic processes e g landslides

continental rift systems and anorogenic magmatism abstract precambrian laurentia and mesozoic gondwana both rifted along geometric patterns that closely approximate truncated icosahedral tessellations of the lithosphere these large scale quasi hexagonal rift patterns manifest a least work configuration for both laurentia and gondwana continental rifting coincided with drift stagnation and may have been driven by lithospheric extension above an insulated and thermally expanded mantle anorogenic magmatism including flood basalts dike swarms anorthosite massifs and granite rhyolite provinces originated along the laurentian and gondwanan rift tessellations long lived volcanic regions of the atlantic and indian oceans sometimes called hotspots originated near triple junctions of the gondwanan tessellation as the supercontinent broke apart we suggest that some anorogenic magmatism results from decompression melting of asthenosphere beneath opening fractures rather than from random impingement of hypothetical deep mantle plumes

investigating uplift in lesina marina southern italy with the aid of persistent scatterer sar interferometry and in situ measurements we apply persistent scatterer interferometry psi techniques to synthetic aperture radar sar data from ers and envisat satellites on the lesina marina area a coastal tourist village in apulia southern italy where the excavation of a canal exposed grey micro and meso crystalline gypsum which is now showing a high density of cavities and sinkholes due to gravitational collapse processes we observe ps objects undergoing displacements along the sensor line of sight forming the same relatively smooth pattern in all the processed data stacks vertical displacement rates derived through integration of ascending and descending geometries reach about 4 mm year on locations adjacent to the canal gently decreasing towards the western end of the built up area high precision leveling measurements performed in 1999 and 2010 reveal a substantial agreement with the envisat psi data taking into account a small bias due to the choice of the leveling reference point the dataset thus validated suggests the presence of an uplift phenomenon going on steadily for the entire timespan covered by the sar observations 1992 2009 these observations supported by petrographic data and in situ investigations seem only in part compatible with a residual diapirism and hint instead to more complex processes such as a combination of diapirism and the hydration of the residual anhydrite in the core of the gypsum mass these results confirm the importance of the integration between in situ geologic and geophysical remotely sensed investigations as the latter often represent an essential tool to infer whether a given phenomenon which can be hypothesized by the former is presently under development

mid crustal magmatic sheets in the cascades mountains washington implications for magma ascent abstract diking diapirism ascent along faults and ascent during heterogeneous ductile flow have all been championed as the most important means of magma ascent in the crust we suggest that these mechanisms are end members in a complex spectrum of ascent processes in an attempt to evaluate which combination of ascent processes formed sheet like bodies in the mid crustal 20 25 km entiat pluton washington we examined the tip regions of these sheets the sheets have length width ratios ranging from 6 to 75 with increasing ratios strongly correlated to decreasing sheet tip radii from 850 to 100 m and decreasing ratios of tip diameter sheet width from 0 66 to 0 33 thus these bodies have geometries falling between those of dikes and those associated with elliptical diapirs the sheets are not associated with faults or fracture zones extending from their tips instead sheet walls are oriented parallel to the axial planes of upright syn emplacement folds in sheets with high length width ratios magmatic foliations in sheets are folded or parallel to axial planes of host rock folds with decreasing length width ratios margin parallel foliations in both sheet and host rock are increasingly common our studies indicate that the sheets are emplaced at high angles to 1 not 3 as proposed in elastic dike models and are always associated with complex viscoelastic flow of host rock these observations rule out elastic dike and fault models and instead favor diapiric rise of magma sheets during viscoelastic behavior of host rock

numerical simulation of seismicity due to fluid injection in a brittle poroelastic medium summary it has recently been shown that rather small perturbations in eiective stress due to uid injection or withdrawal may trigger microseismic events such events typically in the magnitude range below magnitude 4 ml have similar characteristics to normal tectonic earthquakes with double couple focal mechanisms implying a dominant shear motion at the source in this paper we examine the nature of this mechanical uid rock interaction for the case of uid injection in a hydrocarbon reservoir our model is based on the combination of a model of seismicity in dry rocks and a model of pore uid pressure diiusion the former involves a nite diierence approximation of the equation of motion and the latter follows a lattice boltzmann approach they are coupled via the concept of eiective stress applied both to the mohr coulomb rupture criterion and to the volumetric elastic deformations which in turn perturb the pore pressure the simplifying assumptions are that the uid and solid phases have the same bulk moduli and that strain compatibility conditions are not included 2 d plane strain simulations of uid injections in an anisotropically pre stressed elastic brittle medium illustrate the capabilities of the model spontaneous inception and growth of shear fractures in both the near and far elds and explicit calculation of their seismic radiation which feeds back into pore pressure perturbations they also show that as expected the amount and rate of stress drop during the brittle rupture control the size and spatial density of the resulting fractures our model should prove to be relevant at least in two cases as a simulation tool in the investigation of correlations between injection and producer wells which are thought to be of geomechanical origin in certain oil elds and as a forward model in the inversion of focal mechanisms of pore pressure induced shear events

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

viscosity ratio estimates from natural rayleigh taylor instabilities the geometry of natural gravity driven overturns potentially contains information on viscosity ratios of the material involved irregularities at the interface between two superposed horizontal fluid layers tend to amplify and grow with time with a regular wavelength if the top iayer is more dense published formulas woidt for such rayleigh taylor r t instabilities have been used to construct graphs which can constrain the effective viscosity ratio at the onset of the overturn only the initial thicknesses of the two layers and the final wavelength of the structures need be known the theory is based on an infinite two layer system of newtonian fluids between rigid boundaries with no slip or free slip at contacts geological examples included are soft sediment dewatering on the scale of decimetres in northern norway an unusual instability between basalt and sand in australia of hundreds of metres salt diapirism of kilometres in germany and the persian gulf and granitic diapirism from northern sweden of tens of kilometres viscosity ratios in the order of 1 10 are found for soft sediments with the top layer as the more viscous ratios inferred from patterns of salt diapirs are very large with the overburden approximately 103 105 times more viscous than the salt the viscosities of granites are indicated as lower than their overburden and with ratios of 103

positive fault inversion triggering intrusive diapirism an analogue modelling perspective understanding the formation and the development of salt structures is very important especially because they are of significant economical interest for hydrocarbon trapping and for long term storage of radioactive waste and energy reserves generally the activity of normal faults developed in extensional regimes is considered the most efficient mechanism for salt diapirs the results of analogue models reported in this paper suggest a new triggering mechanism for the rise of salt structures during basin inversion this mechanism relates the localization of ductile diapirs to early normal faults only after their inversion during later shortening in this case diapiric growth is related to the strong dip slip reactivation component along the fault extruding the silicone simulating salt upward some natural cases in which the timing and the mechanism of diapiric growth is not clear can be re interpreted in the light of these analogue model results

reservoir depletion and its effect on wellbore stability evaluation abstract production from hydrocarbon reservoirs can lead to decreases in the pore pressures of up to 60 mpa over the lifetime of the field this depletion results in changes of the horizontal stresses acting in the reservoir field data are reviewed and new data presented which define linear decreases of the minimum stress with pore pressure for reservoirs which have undergone pore pressure reductions of 1 8 mpa to 56 mpa the depletion responses cannot be accurately predicted using the most commonly used linear elastic relationship due to either inappropriate boundary condition assumptions or incorrect input values relationships for three different boundary conditions and two material responses are presented which can potentially be used to describe the minimum stress depletion response of reservoirs the significance of the change in the horizontal stress anisotropy with depletion for different boundary conditions is also discussed finally the impact of the stress depletion response on wellbore stability is assessed for inclined wells focussing on openhole production wells whose stability can significantly decrease with depletion

the origin typology spatial distribution and detrimental effects of the sinkholes developed in the alluvial evaporite karst of the ebro river valley downstream of zaragoza city ne spain three types of sinkhole have been mapped in a 50 km2 stretch of the ebro river valley downstream of zaragoza large collapse sinkholes large shallow subsidence depressions and small cover collapse sinkholes the sinkholes relate to the karstification of evaporitic bedrock that wedges out abruptly downstream giving way to a shale substratum twenty three collapse sinkholes up to 50 m in diameter by 6 m deep and commonly hosting saline ponds have been identified in the floodplain they have been attributed to the upward stoping of dissolutional cavities formed within the evaporitic bedrock by rising groundwater flows twenty four large shallow subsidence depressions were mapped in the floodplain these may reach 850 m in length and were formed by structurally controlled interstratal karstification of soluble beds halite or glauberite and gypsum by rising groundwater flow and the progressive settlement of the overlying bedrock and overburden sediments a total of 447 small cover collapse or dropout sinkholes have been recognized in a perched alluvial level along the southern margin of the valley these sinkholes result from the upward propagation of voids through the alluvial mantle caused by the downward migration of detrital sediments into dissolutional voids the majority of these sinkholes commonly 1 5 2 m in diameter are induced by human activities over the karstic bedrock there is a significant increase in sinkhole density downstream this is interpreted as being a result of the evaporitic bedrock wedging out and the convergence of the groundwater flow lines in the karstic aquifer the collapse sinkholes in this area locally with a probability of occurrence higher than 140 sinkholes km2 year cause substantial damage to the linear infrastructures buildings and agriculture and they might eventually cause the loss of human lives copyright 2006 john wiley sons ltd

large depressions thickened terraces and gravitational deformation in the ebro river valley zaragoza area ne spain evidence of glauberite and halite interstratal karstification abstract in the studied reach of the ebro valley the terrace and pediment sediments deposited over glauberite and halite bearing evaporites show local thickenings 50 m recording dissolution induced synsedimentary subsidence recent data on the lithostratigraphy of the evaporite sequence allow relating the alluvium thickenings with either halite or glauberite dissolution the alluvium filled dissolution basin underlying the youngest terraces t8 t11 is ascribed to halite karstification the top of a halite unit approximately 75 m thick is situated 40 15 m below the valley bottom the thickenings of terrace t1 t7 and pediment sediments are attributed to interstratal glauberite karstification 1 coincidence between the elevation range of the terraces and that of the glauberite rich unit glauberite beds reach 30 and 100 m in single bed and cumulative thickness respectively 2 the exposed bedrock underlying thickened alluvium shows abundant subsidence features indicative of interstratal karstification the most common structure corresponds to hectometer scale sag basins with superimposed collapses in the central sector of each basin the subsided bedrock is frequently transformed into dissolution collapse breccias showing a complete textural gradation from crackle packbreccias to chaotic floatbreccias and karstic residues 3 paleokarst exposures show evidence of karstification confined to specific beds made up of secondary gypsum after precursory glauberite partly dissolved and partly replaced despite the magnitude of the subsidence recorded by the thickened alluvium and unlike nearby tributaries the terraces show a continuous and parallel arrangement indicating that the fluvial system was able to counterbalance subsidence by aggradation a number of kilometer size flat bottom depressions have been developed in the valley margin typically next to and inset into thickened terrace and pediment deposits the subsidence structures exposed in artificial excavations excavated in the bottom of some depressions and the correlation between the altitudinal distribution of these basins and that of the glauberite rich unit reveal that subsidence related to interstratal glauberite karstification is the main process involved in their genesis this research ascribes for the first time the thickenings and deformation of specific terrace levels and pediment levels and the development of large karstic depressions to interstratal karstification of exceptionally thick glauberite units

ert gpr insar and tracer tests to characterize karst aquifer systems under urban areas the case of quebec city abstract urban infrastructures built over karst settings may be at risk of collapse due to hydro chemical erosion of underlying rock structures in such settings mapping cave networks and monitoring ground stability is important to assure civil safety and guide future infrastructure development decisions however no technique can directly and comprehensively map these hydrogeological features and monitor their stability the most reliable method to map a cave network is through speleological exploration which is not always possible due to restrictions narrow corridors passages or high water levels borehole drilling is expensive and is often only performed where the presence of karsts is suggested by other techniques numerous indirect and cost effective methods exist to map a karst flow system such as geophysics geodesy and tracer tests this paper presents the outcomes from a challenging application in quebec city canada where a multidisciplinary approach was designed to better understand the groundwater dynamics and cave paths two tracer tests in groundwater flowing through the cave system indicated that water flows along an approximately straight path from the sinking stream to the spring it also suggests the presence of a parallel flow path close to the one already partially mapped this observation was confirmed by combining ground penetrating radar gpr and electrical resistivity tomography ert techniques and ultimately by observing voids in several boreholes drilled close to the main cave path lowering the water levels at the suspected infiltration zone and inside the karst the infiltration cracks were identified and the hydraulic link between them was confirmed in fact almost no infiltration occurs into the karst system when the water level at the sinking stream drops below a threshold level finally sar interferometry insar using radarsat 2 images detected movements on few buildings located over a backfilled sinkhole intercepted by the karst system and confirmed the stability of the rest of the karst area the knowledge of the flow system described in this paper is used by policy makers to assure civil security of this densely populated area

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

investigating a damaging buried sinkhole cluster in an urban area zaragoza city ne spain integrating multiple techniques geomorphological surveys dinsar dems gpr ert and trenching abstract this contribution analyses a complex sinkhole cluster buried by urban elements in the mantled evaporite karst of zaragoza city ne spain where active subsidence has caused significant economic losses 0 3 million euro the investigation conducted after the development of the area has involved the application of multiple surface and subsurface techniques a detailed map of modern surface deformation indicates two active coalescing sinkholes whereas the interpretation of old aerial photographs reveals the presence of two additional dormant sinkholes beneath human structures that might reactivate in the near future dinsar differential interferometry synthetic aperture radar displacement data have limited spatial coverage mainly due to high subsidence rates and surface changes re pavement and the electrical resistivity tomography ert and trenching investigations were severely restricted by the presence of urban elements nonetheless the three techniques consistently indicate that the area affected by subsidence is larger than that defined by surface deformation features the performance of the ground penetrating radar gpr technique was adversely affected by the presence of highly conductive and massive anthropogenic deposits but some profiles reveal that subsidence in the central sector of one of the sinkholes is mainly accommodated by sagging the stratigraphic and structural relationships observed in a trench dug across the topographic margin of one of the sinkholes may be alternatively interpreted by three collapse events of around 0 6 m that occurred after 290 yr bp or by progressive fault displacement combined with episodic anthropogenic excavation and fill average subsidence rates of 6 6 mm yr and 40 mm yr have been calculated using stratigraphic markers dated by the radiocarbon method and historical information respectively this case study illustrates the need of conducting thorough investigations in sinkhole areas during the pre planning stage including a geomorphic approach a sound geomorphic model is essential for the proper design of the site investigation the interpretation of the data and application of effective mitigation measures once sinkhole areas are developed urban elements largely restrict the applicability and performance of multiple techniques substantially decreasing the feasibility and benefit effort ratio of the investigations

evaluation of trenching ground penetrating radar gpr and electrical resistivity tomography ert for sinkhole characterization this paper explores the suitability and advantages of combining the trenching technique with geophysical surveys ground penetrating radar gpr and electrical resistivity tomography ert for sinkhole characterization in a mantled karst area the approach is applied to two active sinkholes concealed by anthropogenic deposits and formed by contrasting subsidence mechanisms collapse and sagging the ert section acquired across the collapse sinkhole images the clayey fill of the depression as an obvious low resistivity area showing the approximate location of the sinkhole edges spatially dense gpr surveys provide information on the position of the boundaries of the concealed subsidence structures and their three dimensional 3d internal geometry revealing the dominant subsidence mechanism we illustrate the impact of several factors on the quality of the gpr data such as sinkhole size nominal frequency of the antennas antenna shielding and the presence of backfilled excavations and above surface objects trenches provided detailed information on the subsurface structure of the sinkhole subsidence magnitude partitioning of the strain and the position of the sinkhole edges especially when they are deep enough and excavated across the central sector and perpendicular to the boundaries the stratigraphic and structural relationships observed in the trench were then used to infer the spatial evolution of the sinkholes e g enlargement their kinematic behavior episodic versus progressive and to differentiate discrete subsidence events and their associated magnitude numerical dates were used to estimate average subsidence rates and the recurrence of subsidence events such integrated data sets may be used as an objective basis to forecast the future behavior of potentially damaging sinkholes and to assess the associated hazard and risk copyright 2013 john wiley sons ltd

investigation of suspected gulls in the jurassic limestone strata of the cotswold hills gloucestershire england using electrical resistivity tomography abstract an electrical resistivity tomography survey has clearly indicated the presence of substantial vertical zones of contrasting material beneath a set of conspicuous linear surface hollows that cut across a spur forming part of the cotswold hills escarpment in gloucestershire these zones are compared with nearby quarry exposures and are inferred to be gulls graben like structures at least 80 m deep filled with collapsed blocks of bedrock with intervening air filled spaces lying within areas of relatively undisrupted gently dipping strata and which under some circumstances would present a significant geohazard our results confirm the great potential of this non invasive and rapid survey technique for investigating such phenomena and provide an exemplar for comparison with surveys elsewhere to assist identification of similar features

reconstructing the internal structure and long term evolution of hazardous sinkholes combining trenching electrical resistivity imaging eri and ground penetrating radar gpr abstract the approaches aimed at characterising specific damaging sinkholes have received limited attention compared with other ground instability phenomena e g landslides moreover the practicality of the trenching technique in combination with numerical dating and retro deformation analysis for sinkhole site investigations has been barely explored this work illustrates the advantages of combining geomorphic mapping electrical resistivity imaging eri ground penetrating radar gpr and trenching for sinkhole characterisation and shows how the trenching technique contributes to fill significant gaps that neither geomorphic nor geophysical methods can address two large sinkholes 200 m long related to the interstratal karstification of evaporites and generated by contrasting subsidence mechanisms sagging collapse were investigated in the fluvia valley ne spain although gpr data may provide high resolution information on subsidence related stratigraphic and structural features at shallow depth the profiles acquired in the investigated sites with 100 mhz shielded and 40 mhz unshielded antennae provided limited insight into the internal geometry of the sinkholes due to reduced signal penetration related to the presence of conductive clayey material the eri sections satisfactorily imaged the general geometry of the sagging and collapse subsidence structures up to depths higher than 100 m and clearly captured the basal contact of the low resistivity sinkhole fill in the sections with adequate layout and resolution the trenches despite their limited depth ca 5 m allowed us to obtain valuable objective information on several key aspects of the subsidence phenomenon 1 mechanisms deformation style and kinematics progressive versus episodic 2 limits of ground deformation 3 temporal evolution expansion versus contraction 4 chronology and timing of most recent deformation phase 5 rates of subsidence and sedimentation and 6 the role played by subsidence in the development of lacustrine environments and the associated sedimentation patterns

the application of gpr and eri in combination with exposure logging and retrodeformation analysis to characterize sinkholes and reconstruct their impact on fluvial sedimentation this work illustrates the practicality of investigating sinkholes integrating data gathered by ground penetrating radar gpr electrical resistivity imaging eri and trenching or direct logging of the subsidence affected sediments in combination with retrodeformation analysis this mutidisciplinary approach has been tested in a large paleosinkhole developed during the deposition of a quaternary terrace on salt bearing evaporites the subsidence structure exposed in an artificial excavation is located next to puilatos a village that was abandoned in the 1970s due to severe subsidence damage detailed logging of the exposure revealed that the subsidence structure corresponds to an asymmetric sagging and collapse paleosinkhole with no clear evidence of recent activity the sedimentological and structural relationships together with the retrodeformation analysis indicate that synsedimentary subsidence controlled channel location the development of a palustrine environment and local changes in the channel pattern gpr profiles were acquired using an array of systems with different antenna frequencies including some recently developed shielded antennas with improved vertical resolution and penetration depth although radargrams imaged the faulted sagging structure and provided valuable data on fault throw they did not satisfactorily image the complex architecture of the fluvial deposit eri showed lower resolution but higher penetration depth when compared to gpr roughly capturing the subsidence structure and yielding information on the thickness of the high resistivity alluvium and the nature of the underlying low resistivity karstic residue developed on top of the halite bearing evaporitic bedrock data comparison allows the assessment of the advantages and limitations of these complementary techniques highly useful for site specific sinkhole risk management this article is protected by copyright all rights reserved

critical stress localization of flow associated with deformation of well fractured rock masses with implications for mineral deposits fluid flow and deformation of fractured rock masses is investigated using numerical models based on distinct element methods udec which couple mechanical and hydraulic behaviour a series of numerical experiments is presented in which diffuse flow through fracture networks changes to highly localized flow at a critical stress state slip on parts of the fracture network causes the opening up of some fractures often at fracture intersections thus a change in the stress state results in a sudden localization of deformation and fluid flow a series of plots of hydraulic conductivity v differential stress are presented for some natural fracture networks to demonstrate the influence of fracture network geometry and in situ stress on the critical phase boundary between diffuse and localized flow the onset of localized deformation and fluid flow is a critical point phenomenon resulting in fractal properties fractal and multifractal techniques are used to characterize heterogeneity of the flow in order to generalize the results of the modelling of discrete systems to a continuum based description of the flow the significance of the models and their implications for crustal behaviour are discussed in relation to hydrothermal mineralization and natural vein systems

spreading of salt structures in the gulf of mexico abstract past and present overhangs on diapirs ductile intrusions of salt are potential hydrocarbon traps and increasing numbers of larger overhangs are being recognised as seismic acquisition and processing improves salt overhangs develop by three process drag by ductile surroundings sinking around salt diapirs thinning of diapiric stems or the topic considered here gravity spreading gravity spreads salt where it is easier for salt to flow sideways than it is to float or sink the potential level to which individual salt diapirs rise depends on the pressure applied to their source by the overburden load and any lateral forces the potential level to which salt diapirs rise can be independent of both the top free surface and the level of neutral buoyancy of the salt even the most vigorous diapirs cannot rise indefinitely they gravitationally spread at barriers they cannot penetrate below at or above their level of neutral buoyancy it has been suggested that salt diapirs spread below their level of neutral buoyancy in weak layers beneath stiff barriers however no case of deep subsurface salt spreading appears to have been documented instead shales rise with salt along the us gulf coast some salt diapirs in the gulf of mexico may simulate ductile ice flows and spread both upwards and downwards to a subsurface level of neutral buoyancy in surroundings of similar strain rate however most diapirs in the gulf are driven above their level of neutral buoyancy so that they spread downwards back towards it these spread over denser or stifter layers in less dense and weaker barriers of air water or unconsolidated sediments this work focuses on the geological implications of the shapes of the tops of small scale secondary salt bodies that spread superficially in weaker and less dense barriers under the northern gulf of mexico analytical material and natural models are used to show that the shape of the top free surface of spreading salt contains information about both the properties of the materials involved and their kinematics many salt diapirs in the gulf spread downslope from viscous salt fountains in muds over sand salt flowing downslope towards a lower level of neutral buoyancy exhibits dynamic extrusion the temporary dynamic nature of salt sheets is emphasised by restating standard arguments for overburden strength in terms of low strain rates contrary to recent views that salt spreading occurs in weak horizons during fast sedimentation it is argued that most salt spreads superficially during periods of slow sedimentation small salt laccoliths advance downslope at long term rates between 1 and 5 mm a after burial spreading and gliding of their overburdens can detach such laccoliths from their source and smear them to salt sills that advance downslope at 8 mm a as development wells are likely to be complicated by such active salt flow we should begin now direct measurements of the rates at which salt spreads at superficial levels beneath the northern gulf of mexico

actual extension of sinkholes considerations about geophysical geomorphological and field inspection techniques in urban planning projects in the ebro basin ne spain abstract aerial photographs historical cartographies and field inspection are useful tools in urban planning design on mantled karst because they permit a wide time interval to be analyzed in the case of zaragoza city several works have confirmed the interest of these approaches in configuring the urban planning code and therefore represent a promising technique nevertheless some caveats should be taken into account when using this kind of information a detailed analysis is presented comparing in a case study from the surroundings of zaragoza geomorphological historical analysis and field inspection with geophysical data field inspection in a noncultivated area permits the constraint of the presence of karst indicators below the geomorphological resolution of aerial photographs and shows results consistent with geophysical surveys the studied case shows an inner zone coinciding with the sinkhole mapped from aerial photographs that correlates with changes in the position of the substratum and changes in thickness of alluvial sediments the integrated analysis permits us to define an external subsidence ring around the geomorphological sinkhole whose surface is twice the size of the inner zone this outer ring is indicated by geometrical changes in gpr profiles increases of thickness of the conductive shallower unit toward the collapse and small collapses on marginal cracks these results support the higher extension of karst hazards linked to sinkholes with respect to their geomorphological expression and the needed detailed analysis to constrain the real sinkhole size or the use of security radii surrounding this surficial evidence when geomorphological data is used for the hazard analyses or the urban planning at karstic zones

geological and environmental implications of the evaporite karst in spain in spain evaporite outcrops cover approximately 7 of the total area of the country most of the evaporitic formations are made up of ca sulfates gypsum anhydrite or ca sulfates and halite certain paleogene marine evaporites also contain k mg chlorides and some tertiary continental formations bear substantial amounts of na sulfates in the subsurface glauberite and thenardite mesozoic evaporitic formations commonly wedge out towards the ground surface passing into condensed sequences and dissolution collapse breccias some of these highly porous breccias constitute major regional aquifers in several areas interstratal karstification of the evaporites has given rise to gravitational deformations such as basin structures monoclines and collapse structures covering several square kilometers that record a cumulative subsidence in excess of 200 m teruel and calatayud grabens a widespread consequence of evaporite dissolution processes in spain is the hydrochemical degradation of surface waters some of the largest and most outstanding lake systems from an environmental perspective occur in karstic depressions developed in evaporitic formations fuente de piedra gallocanta bujaraloz and banolas lakes sinkhole activity is a major geohazard in several evaporite karst areas the sinkhole risk has a particularly high impact in sectors where tertiary evaporites are overlain by quaternary alluvial aquifers calatayud zaragoza and madrid areas some of the detrimental effects of subsidence include severe damage to historical monuments calatayud the demolition of a whole village puilatos or the derailment of a freight train zaragoza area the deepest gypsum caves are found in triassic diapiric structures el sumidor cave 210 m deep and the longest ones are developed in horizontally lying neogene sequences sorbas caves and estremera maze cave the cardona diapir hosts salt caves up to 4 300 m long whose genesis is related to flooding of mine galleries caused by the interception of a phreatic conduit the main anthropogenic impacts on the endokarstic systems are related to the disposal of wastewaters and the destruction of caves by quarrying the fluvial valleys that cross tertiary evaporitic outcrops commonly show peculiar geological characteristics related to dissolution induced synsedimentary subsidence phenomena 1 thickened alluvium filling dissolution basins up to several tens of kilometers long and more than 100 m deep the largest thickenings are found in areas where the bedrock contains halite and glauberite 2 superimposed alluvial units locally bounded by angular unconformities 3 abundant deformational structures and paleosinkholes related to the rockhead and or interstratal karstification of the substratum these fluvial valleys typically are flanked by a prominent gypsum escarpment rock falls favored by the dissolutional enlargement of joints derived from these scarps are the type of mass movement which has caused the highest number of casualties in spain

reconstructing the geochronological evolution of large landslides by means of the trenching technique in the yesa reservoir spanish pyrenees abstract detailed geomorphological mapping has revealed that the slopes upstream of the yesa dam are affected by several flysch landslides the largest landslides correspond to la refaya rotational slide 11 million m3 situated just upstream of the spillway and el vertedero translational slide 6 million m3 located 1 5 km upstream of the dam a portion of el vertedero landslide 3 million m3 was reactivated in 2006 due to overloading caused by an earth heap a higher earth dam will be built on the downstream side of the existing gravity concrete dam to raise the maximum water level of the reservoir by 23 m the retrodeformation analysis of the deposits exposed in two trenches excavated in the upper part of these landslides together with the obtained absolute ages c14 and osl have provided information on the kinematics and evolution of these slope movements the main findings derived from the 45 m long trench dug in the closed depression developed at the foot of the head scarp of la refaya landslide include 1 the landslide is older than 12 ka and has undergone a cumulative rotation higher than 17 yielding a mean rotation rate of about 1 4 millennium 2 most of the rotation 14 occurred before 5 8 ka and according to the trench stratigraphy the kinematics of the landslide has been dominated by progressive displacement no evidence of catastrophic reactivation has been found the 45 m long trench excavated across the scarp and bench situated at the head of the non reactivated portion of el vertedero translational slide reveals that 1 the landslide is older than 38 ka 2 the trenched portion has undergone at least one reactivation subsequent to 20 ka and has remained inactive for a long time as suggested by the highly degraded bedrock scarp with a slope of 18 compared to the 60 dip of the underlying failure plane based on this study corrective measures with an estimated cost of 11 5 million euros have been designed for this slope the investigation illustrates the usefulness and cost effectiveness of the trenching technique allied with geochronological methods to obtain information on the precise limits age failure mechanism kinematics progressive vs episodic displacement movement rate and chronological evolution of landslides

implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults abstract reservoirs associated with salt diapirs that are circular or elliptical in plan view can be segmented by radial faults concentric faults both or neither explanations for this variation are offered based on integration of fault kinematics published studies and seismic examples strata around diapirs can be divided into three structural domains with characteristic fault styles 1 roof zone between the present day depositional surface and crest of a buried inactive diapir this zone is characterised by doming radial faults and occasionally conic graben doming is usually caused by differential compaction and increases with depth 2 a steeply dipping sheath of strata surrounds the diapir out to a distance of less than one diapir radius recording near surface diapir growth in poorly lithified sediments these contain early gravity slumps and late concentric extensional faults regional layer bound polygonal fault systems form radial faults within approximately one diapir radius the only significant radial faulting mechanism below the roof zone 3 diapir root zone of strata whose structural architecture records the diapirs initiating mechanism typically rim synclines or graben that detach on the salt source layer concentric faults at radial distances of a kilometre or more have been found only in root zone rim synclines and sheared sheath strata these models and observations can assist seismic interpretation and structural model building in areas of poor geophysical imaging for instance below overhanging salt

differentiating between gravitational and tectonic faults by means of geomorphological mapping trenching and geophysical surveys the case of the zenzano fault iberian chain n spain abstract the zenzano fault scarp has been developed on the top of a 475 m high erosional escarpment underlain by an upper brittle sequence and a lower halite bearing evaporitic formation the 1850 m long fault with a maximum displacement of 45 m and parallel to the escarpment has offset the back of a dip slope generating an antislope scarp with prominent triangular facets up to 38 m high and obstructing consequent transverse drainages defeated streams both gravitational and tectonic interpretations were previously proposed for this active surface rupture the fault scarp has been investigated by detailed geological and geomorphological mapping geophysical surveys gpr and ert and two trenches excavated across the fault in disrupted drainages the geophysical profiles clearly imaged the fault helping to site the trenches and roughly estimate the thickness of the deposits accumulated in the downthrown block although the maximum displacement to length ratio dmax l of the fault fall within the range of tectonic faults of similar length according to the world database the geological and geomorphological context together with several parameters reveal that this structure corresponds to a gravitational failure 1 anomalously high vertical displacement per event 1 4 m 2 high apparent vertical slip rate 0 6 mm year and 3 short recurrence interval of faulting events the negligible horizontal displacement component on the dip slip fault as well as the presence of very large caprock collapse sinkholes and saline springs strongly suggest that interstratal karstification of the halite bearing evaporites has played a primary role in the development of the gravitational failure the formation of this morphostructure has been favoured by pre existing tectonic faults erosional unloading related to the removal of an overburden ca 800 m thick and enhanced groundwater recharge due to the blockage of the drainage this work illustrates that the proposed multidisciplinary approach allows the identification of features and calculation of parameters that may help to elucidate whether an active failure has a gravitational or a tectonic origin

dynamical similarity and density non proportionality in experimental tectonics abstract the utility of analog laboratory models for tectonic processes relies on their dynamical similarity to their natural prototypes dynamical similarity is often thought to require that the density distribution in the model be a constant position independent multiple of that in the prototype a principle due to hubbert 1937 to clarify the status of this rule we nondimensionalize the equations and boundary initial conditions governing simple models of three paradigmatic processes gravity tectonics compressional tectonics and free subduction the results show that density proportionality while compatible with dynamical similarity is not always required by it in systems with negligible inertia a category that includes most geological and tectonic processes the density proportionality rule is therefore unnecessarily restrictive in many cases implying that the range of analog materials that can be used to construct properly scaled models is wider than commonly recognized

discussion on the north sea silverpit crater impact structure or pull apart basin ken thomson writes the suggestion that the silverpit crater is a pull apart basin smith 2004 and not an impact structure stewart allen 2002 demonstrates that its origin requires further investigation as noted by underhill 2004 the coincidence of the structure with a salt withdrawal basin suggests that halokinesis may provide an alternative mechanism although the model provided by smith involves salt movement it is overly complex as strike slip detachment tectonics are not required instead gravitational collapse of the post salt cover provides a simpler mechanism the southern north sea is dominated by the development of large linear salt swells jenyon 1988 stewart coward 1995 elevation and tilting of the swell flanks results in gravitational instability and a range of deformation styles can develop jenyon 1988 stewart coward 1995 thomson 2004 the instability commonly leads to listric faulting of the post salt cover down slope towards the adjacent salt low jenyon 1988 stewart coward 1995 thomson 2004 detachment levels for the listric faults occur at a number of stratigraphic levels the top of the upper permian zechstein group salt which forms the swells provides a detachment at the base of the post salt cover whilst detachment within the post salt cover in both the triassic rot halite and within the upper cretaceous chalk have also been recognized jenyon 1988 stewart coward 1995 thomson 2004 the majority of the flank collapse faults dip in the same direction as the cover rocks they displace i e towards the salt withdrawal basin and away from the swell but occasionally listric faults can be found which dip away from the salt withdrawal basin towards the swell jenyon 1988 associated with the listric faulting rollover anticlines can develop in the hanging walls stewart coward 1995 whilst slump folds

experimental modeling of role of gravity and lateral shortening in zagros mountain belt dynamically scaled analogs of the geologic structures of the zagros mountain belt are used to argue that different parts of the zagros mountains of iran record different combinations of the effects of a gravity driven overturn and a southwest northeast lateral shortening superimposed on the zagros overturn partially scaled material models have been used to simulate the zagros geodynamics which involve layer parallel compression of a 6 to 7 km thick phanerozoic carbonate cover containing a pattern of preshortening diapirs the folds in the zagros form rapidly 1 5 mm yr in a 20 to 30 km wide zone reactive some of the preshortening diapirs and generate new synshortening listric diapirs a third set of postshortening diapirs rises from the hormuz decollement behind the fold thrust front model buckle folds superimposed on diapirs or pillows tend to avoid and curve around preshortening diapirs which flatten in the synclines model profiles show that lateral shortening induces residual salt at depth to flow toward and rise through the anticlinal cores as synshortening or postshortening diapirs i suggest that any salt pillows in currently diapir free zones of the zagros fold thrust belt may surface as diapirs through the anticlines in the future in the absence of well data seismic and field observations i have used only three map pattern criteria to recognize the timing of diapirs these are locally obscured by extrusive salt sheets preshortening diapirs are generally small and elongate parallel to fold axes and are restricted to synclines synshortening diapirs are elongate perpendicular to the fold axes and are restricted to anticlines postshortening diapirs can be the same size as synshortening diapirs or larger and can be circular they are more common in the anticlines

hidden sinkholes and karst cavities in the travertine plateau of a highly populated geothermal seismic territory tivoli central italy abstract sinkholes and other karst structures in settled carbonate lands can be a significant source of hazard for humans and human works acque albule the study area of this work is a plio pleistocene basin near rome central italy superficially filled by a large and thick deposit of late pleistocene thermogene travertine human activities blanket large portions of the flat territory covering most evidence from geological surface processes and potentially inducing scientists and public officials to underestimate some natural hazards including those connected with sinkholes to contribute to the proper assessment of these hazards a geomorphologic study of the basin was performed using digital elevation models dems recent aerial photographs and field surveys historical material such as old aerial photographs and past geomorphologic studies both pre dating the most part of quarrying and village building was also used together with memories of the elderly population this preliminary study pointed out the presence of numerous potentially active sinkholes that are at present largely masked by either quarrying or overbuilding where this first study pointed out the apparent absence of sinkholes in areas characterized by high density of buildings a detailed subsurface study was performed using properly calibrated electrical resistivity tomography ert and dynamic penetration measurements dpsh together with some borehole logs made available from the local municipality this second study highlighted the presence of sinkholes and caves that are this time substantially hidden to the resolution of standard methods and materials such as aerial photographs dems and field surveys active sinkhole subsidence in the acque albule basin may explain at least in part the frequent damages that affect numerous buildings in the area the main conclusion from this study is that the mitigation of sinkhole hazard in highly populated areas has to pass through a thorough search of hidden sinkholes that can be masked by the anthropocenic molding and blanketing of the territory for these purposes data from historical pre anthropocene documents as well as where possible subsurface investigations are fundamental

a review of the origins of subparallel ridges and troughs generalized morphological predictions from terrestrial models the morphologies of ridges and troughs on earth and the processes involved in their formation are reviewed for application to sets of subparallel ridges and troughs on outer planet satellites we consider tension fracturing normal faulting thrust faulting buckle folding strike slip tectonism fissure eruption wall diapirism surface folding of a flow and near surface laccolithic intrusion the landform characteristics and geologic associations predicted of each process are generalized to be independent of planet specific parameters we find that the combinations of landforms derived from each process are unique making each distinguishable in the idealized case morphological parameters most diagnostic of formational process are ridge and trough cross sectional shape termination style and incipient character the characteristics described are useful in constraining the origin of ridge and trough terrains observed in voyager images and will aid in analysis of high resolution images from the galileo and cassini spacecraft

sinkholes in the salt bearing evaporite karst of the ebro river valley upstream of zaragoza city ne spain geomorphological mapping and analysis as a basis for risk management abstract a detailed sinkhole map has been produced in a stretch of the ebro valley 40 8 km2 including the western sector of zaragoza city ne spain during the last few decades around 70 of the original sinkhole area has been filled with anthropogenic sediments causing the disappearance of 137 ha of wetlands the interstratal karstification of salts halite and glauberite and a wnw ese trending joint set have played a major control in the development of sinkholes three morphometric types of sinkholes have been differentiated each attributed to a specific subsidence mechanism inferred from the paleosinkholes exposed in the surrounding of zaragoza city sagging of bedrock and cover collapse of bedrock and cover and collapse of cover material related to the downward migration of particles through dissolutional conduits each type of sinkhole is characterised by a distinctive behaviour in terms of controlling factors spatio temporal distribution and kinematics and consequently the proposed differentiation may have a practical utility the vast majority of the subsidence damage identified in the area occurs within the boundaries of pre existing sinkholes identifiable in old aerial photographs and topographical maps this fact demonstrates that the application of preventive planning strategies based on detailed geomorphological maps would have allowed avoidance of most of the large financial losses caused by subsidence in the area of the order of hundreds of thousands of euros per year

integrating geomorphological mapping trenching insar and gpr for the identification and characterization of sinkholes a review and application in the mantled evaporite karst of the ebro valley ne spain abstract this contribution illustrates the advantages of integrating conventional geomorphological methods with insar ground penetrating radar and trenching for sinkhole mapping and characterization in a mantled evaporite karst area where a significant proportion of the karstic depressions have been obliterated by artificial fills the main practical aim of the investigation was to elucidate whether buried sinkholes overlap the areas planned for the construction of buildings and services in order to apply a preventive planning strategy old aerial photographs and detailed topographic maps were the most useful sources of information for the identification of sinkholes and helped to obtain information on their chronology either a minimum age or bracketing dates the insar technique provided subsidence rate values ranging from 4 4 to 17 3 mm yr consistent with the spatial distribution of the mapped sinkholes this quantitative deformation data helped corroborating independently the existence of active buried sinkholes and improving the delineation of their limits the gpr profiles contributed to the precise location of sinkhole edges provided information on the geometry of buried sinkholes and deformation structures and helped to site trenches and to rule out the existence of sinkholes in particular areas the main input derived from the trenches includes 1 confirming or ruling out anomalies of the gpr profiles attributable to subsidence 2 precise location of the edge of some filled sinkholes 3 information on subsidence mechanisms recorded by various deformation structures and cumulative subsidence magnitude 4 calculating minimum long term subsidence rates using radiocarbon dates obtained from deformed sinkhole deposits 5 unequivocal evidence of active subsidence in areas assigned for the construction of buildings

rapid subsidence in damaging sinkholes measurement by high precision leveling and the role of salt dissolution abstract investigations dealing with subsidence monitoring in active sinkholes are very scarce especially when compared with other ground instability phenomena like landslides this is largely related to the catastrophic behaviour that typifies most sinkholes in carbonate karst areas active subsidence in five sinkholes up to ca 500 m across has been quantitatively characterised by means of high precision differential leveling the sinkholes occur on poorly indurated alluvium underlain by salt bearing evaporites and cause severe damage on various human structures the leveling data have provided accurate information on multiple features of the subsidence phenomena with practical implications 1 precise location of the vaguely defined edges of the subsidence zones and their spatial relationships with surveyed surface deformation features 2 spatial deformation patterns and relative contribution of subsidence mechanisms sagging versus collapse 3 accurate subsidence rates and their spatial variability with maximum and mean vertical displacement rates ranging from 1 0 to 11 8 cm yr and 1 9 to 26 1 cm yr respectively 4 identification of sinkholes that experience continuous subsidence at constant rates or with significant temporal changes and 5 rates of volumetric surface changes as an approximation to rates of dissolution induced volumetric depletion in the subsurface reaching as much as 10 900 m3 yr in the largest sinkhole the high subsidence rates as well as the annual volumetric changes are attributed to rapid dissolution of high solubility salts

fry spacing of deformed and undeformed modeled and natural salt domes fry s center point spacing strain analysis is applied to experiments of gravity driven overturn of horizontal fluid layers on scales of centimeters or decimeters and to natural salt diapirs on scales of kilometers to tens of kilometers laboratory experiments in which about 100 diapirs formed from initially plane horizontal layers resulted in laterally isotropic spacing and yielded an open circle on a fry plot with a radius equal to the wavelength w lateral deformation and initial departures from horizontal layers with uniform properties may influence w sample experiments of diapirism with and without lateral deformation are compared to natural equivalents the spacing of post late triassic diapirs in the zechstein salt of germany and of post jurassic diapirs in the hormuz salt of arabia yields circles on fry plots which indicate that these gravity structures developed without additional lateral forces fry plots of the spacing of salt diapirs in the zagros mountains define a strain ellipse with the long axis w in arabia parallel and the short axis perpendicular to post miocene regional fold axes the ratio of the zagros strain ellipse is about 1 7 which suggests a northeast southwest shortening of 41 rather than 10 21 as estimated from folding alone this mismatch may be amore result of unquantified shortening due to thrusts and or layer parallel shortening center point spacing of post late triassic domes of zechstein salt in the central north sea also gives an ellipse here the long axis coincides with the direction of middle jurassic to cretaceous extension the axial ratio of the north sea strain ellipse is about 2 8 compared to estimates of about 1 5 2 0 by sclater and christie and 1 8 by wood and barton less

dinsar measurements of ground deformation by sinkholes mining subsidence and landslides ebro river spain differential interferometric synthetic aperture radar dinsar has been applied to detect and measure ground deformation in a stretch of the ebro river valley spain excavated in salt bearing evaporites the capability of the small baseline subset sbas dinsar technique to detect ground displacement is analyzed comparing the dinsar results with the available geomorphological information the deformation map derived from 27 european remote sensing ers satellite images covering more than five years provides sub centimeter displacement measurements in zones coinciding with known active sinkholes and landslides moreover the map provides the first account of mining subsidence in the area the measured deformation rates reach 1 68 cm y for the sinkholes 0 80 cm y for the landslides and 1 45 cm y for the area affected by mining subsidence the sbas dinsar technique provided deformation measurements in a small proportion 5 10 of the known active sinkholes and landslides this limitation is mainly due to the lack of coherence in agricultural areas the spatial resolution of the deformation map pixel size of 90 m and the parallelism between the ers satellite line of sight and the linear escarpment on which most of the landslides occur despite this the interferometric technique provides valuable data that complement traditional geomorphological studies including the quantification of the deformation phenomena the identification of mining subsidence otherwise only recognizable by geodetic methods and the detection of creep deformation which might correspond to premonitory indicators of catastrophic sinkholes and landslides capable of causing the loss of lives detailed dinsar studies combined with field data would be required to improve the analysis of each deformation area copyright 2009 john wiley sons ltd

seismic regime of a single fault model a special experimental technique enabled us to study in detail seismic events on a fault model in a uniaxial stress field the recording system used made it possible to investigate the radiation pattern for all the events observed including the precise determination of the dislocation origin

the dependence of convection planform on mode of heating a fundamental property of a convecting fluid is its planform the distribution in the horizontal plane of hot rising regions and cold sinking regions for the earth s mantle the planform might he visualized as a map of subduction zones hotspots and possibly ocean ridges here i report numerical experiments of convection at high rayleigh number which show a strong dependence of planform on heating mode when heat generation is distributed uniformly through the box the preferred planform consists of an ensemble of time dependent cold axial sinkers distributed in a hot diffuse upward flow when half of the heat is generated within the box and the other half is input through the base the preferred planform consists of an array of hot axial plumes and elongated cold sheets in the former case the mean horizontal wavelength is about equal to the layer depth for the latter it is about twice the layer depth

enigmatic structures within salt walls of the santos basin part 2 mechanical explanation from physical modelling abstract jackson et al this volume used 3d seismic reflection data to describe intrasalt deformation in salt walls in the santos basin they focused on the origin of enigmatic allochthonous salt sheets of older evaporites a1 unit emplaced above overlying stratified evaporites a2 a4 units their kinematic model incorporates i initial inward flow and thickening of a1 salt within the rising wall and arching of a2 a4 overburden ii breaching of the arched overburden ascent of mobile a1 evaporites along single or multiple feeders and emplacement of upper wall sheets or canopies and iii a component of regional shortening within the salt this companion paper uses physical modelling to explain how and why these structures occur and proposes a mechanical basis for the kinematic model our first two models simulated salt having uniform internal density with walls growing by i initially symmetric differential loading and ii initially symmetric differential loading plus shortening these models reproduced anticlines and injection folds seen in the simpler deformed walls in the santos basin however neither model reproduced the most complex structures within the santos evaporites which are i allochthonous intrusions ii steep feeders and iii recumbent synclines thus differential loading and shortening alone are insufficient to generate these complex structures in our third model a less dense lower evaporite a1 was overlain by denser upper evaporites a2 a4 similar to the density structure found by santos basin wellbores the wall rose solely by differential loading in this model a1 breached the overlying evaporites to form vertical diapirs feeding salt sheets and salt wings in the upper part of the salt wall breakthrough of a1 folded a2 a4 evaporites into recumbent synclines model sections closely resemble santos seismic examples suggesting that the key to forming these complex intrasalt structures is a density inversion within the evaporite sequence that creates a rayleigh taylor instability