single layer model for average flow velocity with submerged rigid cylinders abstracta single layer velocity model is proposed in this study to predict the cross sectional average velocity for open channel flows with submerged rigid cylinders this model is preferable to previous two layer models in that it does not involve evaluations of vegetation drag coefficient and hydrodynamic height of roughness elements in the development of the single layer model the concept of the hydraulic radius is applied to determine the length scale of the entire cross section affected by the submerged vegetation the resulting friction factor scales largely with the ratio of stem height to flow depth with exponent 3 2 and also decreases slightly with an increasing reynolds number comparisons of the single layer model with experimental data show that its performance is comparable to the previous two layer models and the model is also applicable to open channel flows subject to submerged flexible vegetation however the proposed model cannot be extended to two extreme conditions including flows

investigation of coseismic and postseismic processes using in situ measurements of seismic velocity variations in an underground mine the in situ mechanical response of a rock mass to a sudden dynamic and static stress change is still poorly known to tackle this question we conducted an experiment in an underground mine to examine 1 the influence of dynamic and static stress perturbations on seismic velocities 2 elastic static stress changes and 3 induced earthquake activity associated with the blast and removal of a portion of hard rock we accurately 0 01 measured seismic velocity variations with ambient seismic noise correlations located aftershock activity and performed elastic static stress modeling overall we observe that the blast induced a sudden decrease in seismic velocities over the entire studied area which we interpreted as the damage due to the passing of strong seismic waves this sudden process is followed by a slow relaxation lasting up to 5 days while seismic activity returns to its background level after 2 days in some locations after the short term effects of the blast have subsided the seismic velocities converge to new baseline levels and permanent changes in seismic velocity become visible after comparing the spatial pattern of permanent seismic velocity changes with elastic static stress modeling we infer that the permanent seismic velocity changes are due to the change in the static volumetric stress induced by the removal of a solid portion of rock by the blast to our knowledge this is the first observation of noise based permanent seismic velocity changes associated with static stress changes

climatology of mesopause region temperature zonal wind and meridional wind over fort collins colorado 41 n 105 w and comparison with model simulations 1 between may 2002 and april 2006 many continuous observations of mesopause region temperature and horizontal wind each lasting longer than 24 h termed full diurnal cycle observations were completed at the colorado state university na lidar facility in fort collins colorado 41 n 105 w the combined data set consists of 120 full diurnal cycle observations binned on a monthly basis with a minimum of 7 cycles in april and a maximum of 18 cycles in august each monthly data set was analyzed to deduce mean values and tidal period perturbations after removal of tidal signals monthly mean values are used for the study of seasonal variations in mesopause region temperature zonal and meridional winds the results are in qualitative agreement with our current understanding of mean temperature and wind structures in the midlatitude mesopause region with an observed summer mesopause of 167 k at 84 km summer peak eastward zonal wind of 48 m s at 94 km winter zonal wind reversal at 95 km and peak summer pole to winter pole meridional flow of 17 m s at 86 km the observed mean state in temperature zonal and meridional winds are compared with the predictions of three current general circulation models i e the whole atmosphere community climate model version 3 waccm3 with two different simulations of gravity wavefields the hamburg model of the neutral and ionized atmosphere hammonia and the 2003 simulation of the thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm while general agreement is found between observation and model predictions there exist discrepancies between model prediction and observation as well as among predictions from different models specifically the predicted summer mesopause altitude is lower by 3 km 8 km 3 km and 1 km for waccm3 the two waccm runs hammonia and time gcm respectively and the corresponding temperatures are 169 k 170 k 158 k and 161 k the model predicted summer eastward zonal wind peaks to 71 m s at 102 km to 48 m s at 84 km to 75 m s at 93 km and to 29 m s at 94 km in the same order the altitude of the winter zonal wind reversal and seasonal asymmetry of the pole to pole meridional flow are also compared and the importance of full diurnal cycle observations for the determination of mean states is discussed

a tectonostratigraphic framework for the mid norway region abstract the tectonostratigraphic analysis presented here aims to establish a broad stratigraphic framework within which the likely distribution of both reservoir and source rock intervals within the deep water voering and more basins can be evaluated in terms of hydrocarbon potential the devonian to triassic interval can be effectively discounted by its extreme depth of burial across most of the study area the middle jurassic is interpreted to provide a potential reservoir target in the gjallar ridge area the cretaceous is seismically mappable across the region and has been divided into five tectonostratigraphic sequences late cretaceous reservoirs are considered to offer targets in the nyk high area six tectonostratigraphic sequences are described within the cenozoic succession paleocene reservoirs are interpreted to offer targets over both the ytterskallen and ormen lange areas of the more basin source rock maturity is critical for exploration success mapping shows the late jurassic earliest cretaceous spekk formation to be overmature over most of the area though the presence of possible dhis indicates the probable presence of major gas accumulations in the region only on the western flank of the vigrid syncline does the spekk shallow sufficiently to lie within the potential oil window it is concluded that the region has the potential to become a significant new hydrocarbon province for the 21st century

differential compaction faults and their implications for fluid expulsion in the northern bozhong subbasin bohai bay basin china abstract a series of differential compaction faults was identified in the northern bozhong subbasin bohai bay basin china by using 3d seismic well log and lithology data the differential compaction faults display two obvious characteristics first they develop along a lithologic boundary which separates thick sandstone from underlying mudstones facies and thickness change such as an abrupt lithologic change between sandstone and mudstone a lateral thickness change of overlying sandstone are the basic controlling factors of these differential compaction faults second they have a definite strike direction according to the fault strike the differential compaction faults can be divided into three groups group a have an approximate orthogonal strike with the tectonic faults group b display a similar strike with the slope and group c show radial strikes on the circular basement uplift tectonic faults influence the planform patterns of differential compaction faults in their near vicinity and induce these faults displaying an approximate orthogonal intersection with the late period through going faults group a basin slope promote the formation of differential compaction faults by downslope gravity sliding and cause faults parallel to the strike of slope group b circular basement topography generates isotropic stress and leads the differential compaction faults above the basement dominated by radial strikes group c production and geochemistry data is an evidence of differential compaction faults developed in a late period when the strata reach a certain burial depth that the source rocks enter the oil generating window the presence of thermogenic fluid within shallow reservoirs represents as evidence of hydrocarbon drained and migrated through the differential compaction faults the differential compaction faults could serve as significant conduits for fluid expulsion and hydrocarbon accumulation in the bohai bay basin china

paleo pressure evolution and its origin in the pinghu slope belt of the xihu depression east china sea basin abstract the xihu depression in the east china sea basin is one of the prime gas and light oil producing regions of eastern china overpressure evolution and origin in the sandstone reservoirs of the pinghu e2p formation in the pinghu slope belt of the xihu depression were investigated through a combination of fluid inclusion analyses and basin numerical modeling combined with measured pore pressures drill stem and wireline formation tests well loggings gas geochemistry and casting thin section data four oil inclusion types exhibiting different api gravities and hydrocarbon gas inclusions were identified using inclusion petrography microscopic fluorescence and raman spectra homogenization and ice melting temperatures of coeval aqueous inclusions determined using microthermometry combined with burial thermal histories determined by basin numerical modeling suggested multiple episodes of oil and natural gas charge in the e2p reservoirs from the miocene to the present day pore pressure evolution history reconstructed with fluid inclusion pvtx analysis indicated that the pinghu formation experienced three phases overpressure generation followed by overpressure release and then further overpressure generation the first phase of weak overpressure was generated during burial in the middle late miocene currently it is hard to definitely determine the origin of the first phase of overpressuring nevertheless it can be speculated that the origin may be related to disequilibrium compaction oil generation and tectonic compression based on burial tectonic and hydrocarbon generation histories following this a sudden uplift of formations led to overpressure release in the late miocene and then the second phase of moderate overpressure generation occurred during burial in the late pliocene and quaternary based on well log signatures vitrinite reflectance data of mudstones and gas geochemistry combining with seismic analysis the second phase of overpressuring was interpreted to have been mainly caused by fluid expansion which resulted from local gas generation by kerogen maturation and long distance vertical and lateral pressure transfer

the development of polygonal fault systems by syneresis of colloidal sediments abstract polygonal fault systems occur in numerous sedimentary basins worldwide are generally located on passive margins in onlap fill units and tend to comprise the finest grained sediments in this geological setting these fault systems have been most thoroughly described in the central north sea basin and the detailed structure shows a significant correlation with lithological variations both vertically and laterally extension measured in stacked decoupled tiers of polygonal faults correlates positively with both clay fraction and smectite content lateral facies variations are also observed and indicate that time equivalent sequences upslope from the smectite rich polygonally faulted sediments are coarse grained clay poor and undeformed this leads us to believe that the structure and geometry of the fault system are controlled by the colloidal nature of the sediments and that the volumetric contraction measured on seismic sections can be accounted for by syneresis of colloidal smectitic gels during early compaction syneresis results from the spontaneous contraction of a sedimentary gel without evaporation of the constituent pore fluid this process occurs due to the domination of interparticle attractive forces in marine clays dependent on environment and is governed by the change of gel permeability and viscosity with progressive compaction the process of syneresis can account for a number of structural features observed within the fault systems such as tiers of faults the location of maximum fault throw and growth components at upper fault tips as such this paper represents the first attempt to correlate microscale properties of clay rich sediments to their macroscale seismic character

discussion on development of polygonal fault systems a test of hypotheses d m d james writes the mechanics of formation of polygonal faults are widely acknowledged as not yet fully understood and it is welcome that goulty swarbrick 2005 attempt a discriminatory test between rival hypotheses it is however important that such a test bears some relation to physical reality the test is based on the assumption that the ratio of horizontal to vertical effective stress as deduced from leak off tests in two wells in the north sea at depths of about 2 km yields the co efficient of earth pressure at rest therein and hence the residual friction governing the post nucleation development of polygonal faults apparently globally and at any depth it is not clear if the authors consider that the polygonal fault tiers at the well sites are currently active neither is it clear if they assume that the coefficient of residual friction along the fracture is a reasonable approximation to the coefficient of initial friction which governs the dip of the propagating fracture tip and the fault surface as a whole relative to the orientation of the vertical effective stress it is hardly surprising that the ratio of horizontal to vertical effective stress k is very high in the wells analysed the leak off tests are from highly overpressured horizons ratios of pore fluid pressure to total vertical stress approximately 0 80 and 0 84 and the effect of pore fluid pressure coupling hillis 2003 will inevitably decrease the value of the horizontal effective stress to lesser extent than it does the vertical effective stress it is certainly not yet demonstrated that polygonal faults require overpressures of this magnitude for their formation by any mechanism leak off tests tend to overestimate the horizontal effective stress if no correction is made for the excess mud pressure necessary to overcome the tensile strength of

polygonal faults and their implications for hydrocarbon reservoirs in the southern qiongdongnan basin south china sea the polygonal faults were identified in qiongdongnan basin south china sea by using the technique of time coherent slice and horizon flattening of high resolution 3d seismic data these polygonal faults occur in three tiers of the upper meishan formation and the huangliu formation the faults have lengths of 150 1500 m spacings of 50 3000 m throws of 10 40 m and dips of 50 90 degrees tectonic evolution in the qiongdongnan basin can be divided into a rifted stage and a post rifted stage tectonic faults are widely distributed in the rifted sequences but are not well developed in the post rifted stage few faults in the post rifted sequences might suggest the absence of a migration pathway for hydrocarbon or other fluids however the existence of polygonal faults in the post rifted sequences can serve as the pathway and promote the hydrocarbon migration and accumulation in the qiongdongnan basin during the post rifted stage c 2010 elsevier ltd all rights reserved

the geometry and emplacement of conical sandstone intrusions conical sandstone intrusions with a geometry comparable with that of many igneous sills have been identified using 3d seismic data from large areas of the north sea and faeroe shetland basins these intrusions are of reservoir scale ranging from 100 to 2000 m or so in diameter 50 300 m in height and 1 80 m in thickness aperture they are concentrated in specific stratigraphic intervals in the cenozoic fills of both basins two geometrical end members are recognised and defined here apical cones and flat based bowls the former consist of inward dipping conical inclined sheets meeting at a prominent apex and the latter of similarly dipping discordant margins climbing from the edges of a concordant sheet both end members are associated with domal folds that are interpreted as resulting from the hydraulic elevation of the overburden during intrusion and which are analogous to similar structures associated with bowl shaped igneous sills measurements of aperture versus distance exhibit systematic relationships with the structural relief of these folds offering a potentially predictive method for estimation of sandstone intrusion aperture and reservoir volume prior to drilling a growth model for these end member geometries is presented drawing on existing theory for igneous sill emplacement aperture versus distance plots x are used to illustrate two contrasting models for aperture inflation during propagation but these require much further data before any specific growth model can be adopted

an integrated approach for the prediction of subsidence for coal mining basins abstract in this study land subsidence caused by underground mining activities was investigated by means of a new subsidence prediction approach isp tech which takes into account the most important parameters contributing subsidence development such as coal production methods depth mining sequence and other geomechanical characteristics of underground rock strata etc isp tech can be applied to operating mines to keep land subsidence under control as well as virgin coal sites to predict surface subsidence prior to mining activities in the method geological information gathered from the geographic information system gis and the mining information system mis are utilised to obtain geological cross sections which are used in finite element models for mesh building then a number of two dimensional finite element modelling analyses are carried out to determine land subsidence occurring due to mining operations finally land subsidence predicted from modelling studies is compared to the gps and or differential interferometry synthetic aperture radar din sar measurements if incompatibility of the results is detected finite element meshes should be optimised and then reanalysed to obtain more compatible results in the study two different case studies were given as examples of the application of isp tech results of the case studies showed that isp tech can successfully be applied to complex mine subsidence problems the proposed approach gives more accurate results than those obtained from other classical subsidence prediction methods

kilometre scale polygonal seabed depressions in the hatton basin ne atlantic ocean constraints on the origin of polygonal faulting polygonal faulting is a widespread phenomenon in sedimentary basins worldwide it changes basin scale fluid flow patterns and alters the physical properties of the sediments making it important for hydrocarbon exploration and geohazard analysis it is generally accepted that polygonal fault patterns derive from dewatering and compaction of the host sediments but there is debate regarding the processes that control polygonal faulting new multibeam bathymetry data from the hatton basin ne atlantic show up to 10 m deep and 200 600 m wide troughs at the seabed they connect to each other forming polygons that are several hundred metres across i e of similar size as buried polygonal fault systems observed in 3d seismic data the troughs are symmetrical and resemble elongated pockmarks previously unpublished high resolution 2d seismic data from the same area show seismic disturbance zones similar to pipes observed under pockmarks elsewhere as well as faults that have all the characteristics of polygonal fault systems the observation of the wide disturbance zones is enigmatic as they appear to follow the polygonal seafloor pattern the observed extent of the polygonal sediment contraction system is substantial covering almost 37 000 km2 we calculate that some 2600 km3 of possibly carbon bearing fluids have been expelled from this system and we expect that this will affect the benthic ecosystems although so far there is only limited evidence for chemosynthetic habitats

development of polygonal fault systems a test of hypotheses polygonal networks of normal faults in layer bound sequences of fine grained mudstones have formed without regional tectonic extension the two leading hypotheses concerning the generic mechanism responsible for their development are 1 horizontal stresses are reduced by syneresis 2 coefficients of residual friction are very low to discriminate between these hypotheses the ratios between the minimum horizontal and the vertical effective stresses have been estimated in four north sea wells penetrating oligocene and miocene sequences that contain polygonal fault networks the effective stress ratios are c 0 8 consistent with very low coefficients of friction but not with syneresis

application of the extracted volume of a deposit as a measure of deformation for seismic hazard evaluation in mines abstract induced seismicity in mines is caused by rock deformation due to the extraction of part of the rock volume it is assumed that the deformation of the rock mass is proportional to the volume of deposit excavated the probabilistic dependence of seismic energy on the volume of deposit extracted was used in an attempt at continuous evaluation of seismic hazard in mines this evaluation has the character of a long term forecast but together with other geophysical methods it may also act as a short term forecast of large tremors examples are given of the application in a few underground mines

seismic interferometry turning noise into signal turning noise into useful data every geophysicist s dream and now it seems possible the field of seismic interferometry has at its foundation a shift in the way we think about the parts of the signal that are currently filtered out of most analyses complicated seismic codas the multiply scattered parts of seismic waveforms and background noise whatever is recorded when no identifiable active source is emitting and which is superimposed on all recorded data those parts of seismograms consist of waves that reflect and refract around exactly the same subsurface heterogeneities as waves excited by active sources the key to the rapid emergence of this field of research is our new understanding of how to unravel that subsurface information from these relatively complex looking waveforms and the answer turned out to be rather simple this article explains the operation of seismic interferometry and provides a few examples of its application

structural features and formation conditions of mud diapirs in the andaman sea basin data from offshore oil and gas explorations have revealed that mud diapirs occur widely not only at continental margins but also in foreland basins and may have played an important role in the entrapment of oil and gas although the structural features and formation mechanism of salt diapirs have been extensively investigated mud diapirs are still not fully understood largely due to the difficulty of identifying them from seismic data in this paper the structural features and main controlling factors of mud diapirs in the andaman sea basin are investigated based on seismic profiles combined with drilling data and regional tectonic settings the results show that there are five types of mud diapir in the andaman sea basin turtleback mud diapir mud dome piercing mud diapir mud volcano and gas chimney like mud diapir turtleback mud diapirs mainly occur in the southern segment of the accretionary wedge of the andaman sea basin which is far from the bengal fan and characterized by low deposition rate and strong compression tectonic setting piercing mud diapirs exist mainly in the central segment of the accretionary wedge which is close to provenances of sediments and characterized by rapid sedimentation rates large mudstone thickness and transpressional tectonic setting mud domes and mud volcanoes mainly occur in the northern segment of the accretionary wedge which is characterized by rapid sedimentation rates large mudstone thickness and sedimentary wedge growth tectonic setting the gas chimney like mud diapirs only occur in the northern segment of the back arc depression close to the sagaing strike slip fault belt which is characterized by high deposition rate large mudstone thickness and high geothermal gradient these features suggest that thick mudstone deposit rapid sedimentation rates large geothermal gradient strong tectonic stress and gravitational spreading and sliding may have prompted the formation of mud diapirs in the andaman sea basin

small scale faulting in the upper cretaceous of the groningen block the netherlands 3d seismic interpretation fault plane analysis and regional paleostress abstract over the last years field based studies have shown that fault surfaces can exhibit a considerable self affine topography it is reasonable to assume that similar undulations are also present in fault interpretations from 3d reflection seismic data however both the interpretation uncertainty and geophysical resolution limits hinder their analysis this study analyses a set of small scale non reactivated faults in the upper cretaceous chalk group upper ommelanden formation of the nw part of the groningen block the netherlands in a high quality pre stack depth migrated 3d seismic data set the studied faults are fully contained inside the chalk group in an area located between the major tectonic bounding faults of the nw groningen block over 200 faults with offsets in the order of 30 50 m were interpreted across an area of ca 150 km 2 showing a clear preferential orientation for strike dip and dip direction detailed interpretations and 3d fault plane analyses show undulations on the fault plane we show that these undulations are not an interpretation or gridding artefact and interpret these to indicate direction of fault slip these results were used to calculate a paleostress tensor using all faults to calculate a single stress tensor for the entire study area by numerical dynamic analysis based on the orientation position and a thickness analysis it is interpreted that these faults formed due to the tectonic reactivation of salt structures in the latest cretaceous the calculated paleostress state shows a general nw se extension with a vertical maximum principle stress and a stress ratio of about 0 3 indicating that the studied faults are not the result of dewatering this interpretation agrees both with a nearby salt tectonic reconstruction as well as field based paleostress results from the uk belgium and france a first look at other surveys from the dutch sector indicates that similar faults are present in other areas with different orientations we propose that a dedicated analysis of these faults across on and offshore europe would allow extending the stress map of the late cretaceous into areas where the chalk is not outcropping

shallow gas accumulations in the german north sea abstract shallow gas here defined as free gas that is trapped in unconsolidated deltaic and shallow marine siliciclastic sediments of plio pleistocene age is found within the topmost 1000 m of sediment in the southern north sea shallow amplitude anomalies in seismic reflection data are likely due to the presence of gas the most prominent and easy to recognize indicators are high amplitude anomalies or bright spots that are widespread within the southern north sea gas from shallow reservoirs is currently produced offshore the netherlands in this study we determine whether there are analogous shallow gas accumulations within the german north sea therefore we screened 2d and 3d multichannel seismic data for shallow amplitude anomalies several clusters of bright spots are identified above salt domes that closely resemble the economic deposits known in the dutch sector in both size and their characteristic multilayered shape three of these potential gas accumulations occurring in combination with additional hydrocarbon indicators such as seismic attenuation and velocity push downs are investigated in detail and compared to shallow gas fields from offshore the netherlands amplitude anomalies indicate gas seepage on the seafloor that may contribute to the atmospheric methane budget and may have an impact on offshore infrastructure

scaling of velocity profiles for depth limited open channel flows over simulated rigid vegetation abstractusing the plane mixing layer analogy a length scale is proposed to normalize velocity profiles for vegetated open channel flows the new scaling is an improvement over those based on the logarithmic velocity defect and power laws in collapsing the velocity profiles which include measurements conducted in this study and also those reported in the literature for a variety of flow and vegetation configurations an eddy viscosity model is also developed to justify the scaling argument this study is limited to rigid vegetation submerged in depth limited flows in which the flow depth is no greater than twice the vegetation height

monitoring velocity changes caused by underground coal mining using seismic noise we use passive seismic interferometry to monitor temporal variations of seismic wave velocities at the area of underground coal mining named jas mos in poland ambient noise data were recorded continuously for 42 days by two three component broadband seismometers deployed at the ground surface the sensors are about 2 8 km apart and we measure the temporal velocity changes between them using cross correlation techniques using causal and acausal parts of nine component cross correlation functions ccfs with a stretching technique we obtain seismic velocity changes in the frequency band between 0 6 and 1 2 hz the nine component ccfs are useful to stabilize estimation of velocity changes we discover correlation between average velocity changes and seismic events induced by mining especially after an event occurred between the stations the velocity decreased about 0 4 based on this study we conclude that we can monitor the changes of seismic velocities which are related to stiffness effective stress and other mechanical properties at subsurface caused by mining activities even with a few stations

the western tyrrhenian sea revisited new evidence for a rifted basin during the messinian salinity crisis abstract in the last fifty years the messinian salinity crisis msc has been widely investigated in the mediterranean sea but a major basin remains fewly explored in terms of msc thematic the western tyrrhenian basin the rifting of this back arc basin is considered to occur between the middle miocene and the early pliocene thus including the msc giving a unique opportunity to study the crisis in a context of active geodynamics however the msc seismic markers in the western part of the tyrrhenian sea have only been investigated in the early eighties and the msc event in the western tyrrhenian basin remains poorly studied and unclear in this study we revisit the msc in the western tyrrhenian basin i e along the eastern sardinian margin we present results from the interpretation of a 2400 km long hr seismic reflection dataset acquired along the margin during the metyss research cruises in 2009 and 2011 the maps of the msc seismic markers reveal that the eastern sardinian margin was already dissected in structurals highs and lows during the msc we also demonstrate that the msc markers constitute powerfull time markers to refine the age of the rifting which ended earlier than expected in the east sardinian basin and the cornaglia terrace these results allow us to discuss the palaeo water depth of the western tyrrhenian basin during the msc as well as implications for possibles scenarios of the messinian salinity crisis across the eastern sardinian margin

deep characterization of the santiago basin using hvsr and cross correlation of ambient seismic noise abstract continuously recorded seismic ambient noise is used to investigate the intermediate and deep structure of the santiago basin for seismic site response evaluation single station h v spectral ratios hvsr were used as a proxy to identify zones with high stiffness soils and low impedance contrast with the underlying bedrock as a complement of available surface geology information frequency domain cross correlation of the vertical components of ambient noise were calculated and used to estimate phase velocity dispersion curves associated to station pairs over different soil deposits in addition noise correlation functions ncfs calculated from time domain cross correlation of the vertical seismic noise records were used to estimate group velocity dispersion curves and to verify results from the spectral method data processing from both methods resolves a frequency band between 0 1 and 8 0 hz a critical band for civil infrastructure that is difficult to determine with traditional local scale passive surface wave methods station pairs with high signal correlation over stiff soils in the center south and east part of the basin mainly associated to flat hvsr response yielded robust phase velocity dispersion curves that vary approximately from 3 5 km s at 0 1 hz to 1 km s at 4 hz shear wave velocity profiles inverted from the dispersion curves show high average shear wave velocities that also have a pronounced increase rate with depth and a lack of clear soil bedrock interface at depths predicted by available gravimetric data

bulls eye pockmarks and polygonal faulting in the lower congo basin relative timing and implications for fluid expulsion during shallow burial abstract this study describes a new type of pockmark association from the lower congo basin offshore west africa consisting of up to 8 stacked paleopockmarks separated by intervals of drape and onlap fill the stacked paleopockmarks occur within the depocentres of polygonally faulted plio pleistocene sediments and are distributed evenly in the downslope parts of two salt mini basins the majority of the stacked pockmarks initiated synchronously in the late pliocene 3 ma with a subordinate initiation phase in the mid pliocene 4 ma the primary agents in pockmark formation are interpreted to be pore water expelled during early stage compaction together with biogenic methane bottom simulating reflections bsrs associated with free gas overlain by gas hydrates are currently found in the area it is speculated that biogenic methane accumulated within and below a clathrate cap which was repeatedly breached forming pockmarks at discrete horizons separated by intervals of draping sedimentation the mid and late pliocene pockmark initiations appear to coincide with sea level falls following periods of relatively stable highstand conditions several subsequent pockmark horizons may similarly correlate with subsequent sea level falls during the late pliocene and early pleistocene the stacked paleopockmarks are completely surrounded by polygonal faults and consistently occur within polygonal fault cells that crosscut the succession containing the stacked pockmarks early stage compaction and dewatering of the pliocene sediments thus preceded polygonal faulting providing a constraint on the conditions leading to polygonal faulting of the fine grained host sediments the relationship documented here is interpreted as due to the presence of a hydrate cap in the plio pleistocene mini basins which may have retarded the normal compaction processes and facilitated pockmark formation by allowing the build up of gas hydrate and free gas in the basin centres the relative timing and spatial relationships implies that fluids expelled due to polygonal faulting were not implicated in pockmark formation in this area

body and surface wave reconstruction from seismic noise correlations between arrays at piton de la fournaise volcano body wave reconstruction from ambient seismic noise correlations is an important step toward improving volcano imaging and monitoring here we extract body and surface waves that propagate in piton de la fournaise volcano on la reunion island using ambient noise cross correlation and array processing techniques ambient noise was continuously recorded at three dense arrays each comprising 49 geophones to identify and enhance the green s function from the ambient noise correlation we apply a double beamforming dbf technique between the array pairs the dbf allows us to separate surface and body waves direct and reflected waves and multipathing waves based on their azimuths and slownesses we successfully extract body waves between all the combinations of arrays including the wave that propagates through the active magmatic system of the volcano additionally we identify the effects of uneven noise source distribution and interpret the surface wave reflections

the origin of sedimentary basins a status report from the task force of the international lithosphere program abstract better insights into the mechanisms of basin formation have a direct bearing on the predictive power of forward models for basin fill models that link flexure normal faulting and thrusting on a subbasin scale provide important constraints on the tectonic control of the sedimentary record enabling a quantitative comparsion with eustatic contributions to the basin architecture thus of special importance is the need to link processes with different spatial and temporal scales involved in the evolution of extensional and compressional basins by numerical modelling a new generation of basin modelling concepts and techniques is one of the main objectives of the task force origin of sedimentary basins of the international lithosphere program the focus of this work is on the quantification of the effects of the thermomechanical structure of the lithosphere and its interplay with regional and local stress changes other important developments include the step towards three dimensional modelling and the full integration of rapidly expanding fission track and other data sets to constrain vertical motions in basins as natural laboratories for the interactive testing and development of new basin modelling techniques a number of basins with high quality data from industry government and academia have been selected on the basis of specific testable problems

the limited growth of vegetated shear layers 1 in contrast to free shear layers which grow continuously downstream shear layers generated by submerged vegetation grow only to a finite thickness because these shear layers are characterized by coherent vortex structures and rapid vertical mixing their thickness controls exchange between the vegetation and the overlying water experiments conducted in a laboratory flume show that the growth of these obstructed shear layers is arrested once the production of shear layer scale turbulent kinetic energy ske is balanced by dissipation of ske within the canopy this equilibrium condition along with a mixing length closure scheme was used in a one dimensional numerical model to predict the mean velocity profiles of the experimental shear layers the agreement between model and experiment is very good but field application of the model is limited by a lack of description of the drag coefficient in a submerged canopy

deposition or remobilization of the enigmatic hefring member sand eastern north sea a multidisciplinary approach abstract sand remobilization is a well known and well studied phenomenon and seismic observations particularly from the north sea giant sand injectite province nsgsip combined with outcrop investigations have permitted a good understanding of the physical processes of sand remobilization trigger mechanisms and resulting seismic geometries the degree of remobilization and the distinction between depositional and remobilized injected sand from seismic data alone are however still relatively unconstrained in this study we use a multidisciplinary approach based on seismic stratigraphy petrography and biostratigraphy to investigate an enigmatic and apparently isolated eocene sandstone body the hefring member which in the seismic data shows characteristics of both depositional and remobilized origin we use the available well logs cutting samples and side wall cores to investigate whether we can address the degree of remobilization from seismic data alone by linking the mapped seismic facies with remobilization degree as observed from the well data in addition to addressing the degree of remobilization we propose a model for the formation of the hefring member which includes laterally restricted submarine channel sand deposition and secondary remobilization with mainly upward and lateral injection we infer that the remobilization of the hefring member was controlled by local and rapid differential loading potentially emphasized by activity in the nearby d 1 fault system and triggered by a significant drop in sea level understanding the origin and evolution of the hefring member is important for unravelling the geological development of the area and because the sand member represents a new reservoir unit comparable to the nearby prolific siri canyon sandstone

passive margin evolution and its controls on natural gas leakage in the southern orange basin blocks 3 4 offshore south africa using a 2d seismic dataset that covers part of the southern orange basin offshore south africa we reconstructed the geological evolution of the basin this evolutionary model was then used to investigate the occurrence of natural gas within the sedimentary column and the distribution of gas leakage features in relation to the observed sedimentary and tectonic structures developed in the post rift succession since the early cretaceous the cretaceous succession has been subdivided into five seismic units the highest sedimentation rates occur within the barremian aptian unit c1 and the turonian coniacian unit c3 two cenozoic units t1 and t2 have been distinguished these show a sudden decrease in sedimentation rate for the whole of the cenozoic three phases of gravitational tectonics with two late cretaceous phases of mass movement in the northern study area and cenozoic slumping in the southern study area have been related to sedimentation rates sea level changes paleoenvironmental evolution and regional tectonics the occurrence of natural gas leakage follows a coast parallel distribution within the study area in the near shore part at water depths shallower than 400 m massive gas chimneys penetrate through the sediment layers and reach the near surface within an intermediate narrow band between 300 and 500 m water depth the gas migrates more diffusely through sub vertical faulted cretaceous sediments while in the outer part of the basin through the cretaceous and cenozoic gravitational wedges only very few signs of gas accumulation and migration can be seen along the faults a conceptual model has been established with the aptian source rock generating gas in the outer part of the basin this source rock underlies the cenozoic wedge in the south and the thick cretaceous wedge in the north and is a postulated source for the natural gas within the sedimentary column this thermogenically generated gas does not migrate directly through the gravitational faults and the above lying sediments but moves buoyancy driven up dip along stratigraphic layers to escape through the sediments to the sea floor in the inner shelf area

polygonal fault systems and channel boudinage 3d analysis of multidirectional extension in analogue sandbox experiments abstract a systematic set of analogue models has been carried out to study the structural evolution of a sedimentary pile consisting of superposed brittle and ductile lithologies in a regional context of passive margins the models are composed of silicone representing a ductile basal layer of evaporites or overpressured shales and sand progressively sedimented on top to simulate brittle overburden sediments channels with various shapes are embedded in the silicone deformation is triggered by gravitational instability of the growing sedimentary pile and basal slope angles ranging from 0 to 5 the main results follow a polygonal fault pattern developed due to the 3d boudinage of the overburden sand above the silicone layer during multidirectional extension if a sandy channel was embedded in the ductile base it was immediately cut by faults which were perpendicular to the channel boundaries no matter what the angle between channel and slope direction the boundaries of the channel preferentially localised faults which propagated through the sedimentary pile above ongoing deformation along these faults therefore strongly influenced further accumulation of sediments

case study of seismic hazard assessment in underground coal mining using passive tomography abstract the relation between applied stress and wave velocity is examined firstly at the laboratory scale by using ultrasonic technique subsequently an island longwall face under hard thick strata suffering from the threat of seismic hazards e g rock burst strong tremor was chosen for a case study of passive velocity tomography based on continuous seismic monitoring during mining operation passive tomographic imaging has been used to locate high seismic activity zones and assess seismic hazard around the face the results show that the high velocity and velocity gradient regions correlated well with the high seismic activities occurred in future mining period in addition the high velocity or velocity gradient regions redistributed with the retreat of coalface and large scale movement of key strata passive velocity tomography can be a promising tool to continuously monitor the relatively high stress zone or evaluate seismic hazard in underground coal mining

analytical solutions of velocity profile in flow through submerged vegetation with variable frontal width abstract flow within vegetation is one of the main driving forces for material exchange and energy transfer in wetland systems impacted by vegetation the flow velocity profile illustrates distortions to the classic logarithmic velocity profile and has attracted much attention among researchers different from analytical models of velocity distribution in literature which is mainly suitable for vegetation with uniform frontal width this paper establishes new analytical solutions of the velocity profile for vegetation such as shrub and sedge that have a variable frontal width in the vertical direction a new shape function is proposed under these conditions in which the frontal width exhibits a gradual increase in the vertical direction from bottom up in the vegetation along with different closure models for eddy viscosity in the vegetation layer and surface layer analytical solutions of the velocity profile are derived from the momentum equations good agreement between calculated and measured data shows our analytical model is effective in predicting velocity profiles

source rocks of the german central graben abstract jurassic to lower cretaceous formations are the most important source rocks for hydrocarbons in the southern central graben area within the dutch central graben the lower jurassic posidonia shale formation is the most prolific source for hydrocarbons while the upper jurassic to lowermost cretaceous bo member of the farsund formation plays this role in the danish central graben oil and gas discoveries in the norwegian dutch and danish part of the central graben proved a prolific petroleum system despite limited success of hydrocarbon exploration in the german part of the central graben various indications suggest migration of gas out of active thermogenic source rocks that are closely related to potential shallow gas accumulations these indications include the restricted location of the bright spots above the jurassic graben system the occurrence of gas chimneys underneath these accumulations and geochemical data from offshore the netherlands which support contribution of thermogenic gas the purpose of this study is to assess the potential for generating thermogenic hydrocarbons from upper triassic to lower cretaceous formations for this reason prominent source rocks of the southern north sea i e the posidonia shale formation and the upper jurassic to lower cretaceous hot shales namely clay deep member offshore the netherlands and bo member offshore denmark were mapped in detail these and other potential formations from the late triassic to the early cretaceous are integrated into an existing petroleum system model of the northern german north sea which was modified for the new requirements the results showed that the main source rocks of the southern central graben the posidonia shale formation and the upper jurassic lower cretaceous hot shales are insignificant as sources for commercial hydrocarbon accumulations within the german central graben area that is either due to marginal occurrence or to low maturity however lower to upper jurassic formations such as marine claystones of the aalburg formation and the lower parts of the kimmeridge clay formation as well as coaly intervals of the central graben subgroup are likely to have generated and still generate hydrocarbons

three dimensional consolidation of fine grained sediments current theories of one to three dimensional consolidation are based on the concept of gravitational loading with concomitant expulsion of pore fluid as a result of mechanical rearrangements of particles and porosity reduction however the recent discovery of extensive networks of layer bound fractures forming polygonal patterns in extremely fine grained smectitic clays and chalks suggests that current theory may not adequately explain the consolidation process in such sediments these faults develop during shallow burial and often appear to have been active at the sediment water interface radially isotropic strain suggests that the process of formation was nontectonic measured values of strain suggest that deformation resulted from volumetric contraction of the sediments we argue that the formation mechanism for these fault systems is related to the colloidal properties of the constituent sediments and that as such stresses due to gravity may not be the only factor controlling pore fluid expulsion

the spatial distributions of faults and deep sea carbonate mounds in the porcupine basin offshore ireland localised populations of deep water carbonate mounds occur throughout the ne atlantic margin of ireland the uk and norway but the mechanisms responsible for their nucleation and growth are not well known based in part on the interpretation of seismic data from the porcupine basin offshore ireland it has been proposed previously that deeply rooted faults are present immediately beneath mounds and act as conduits for the vertical migration of mound feeding hydrocarbons several discrete carbonate mound populations or provinces are present in the porcupine basin above a number of distinct fault systems at different levels in the stratigraphy however detailed mapping of the distributions of both mounds and faults for two of these provinces in the northern part of the basin using 3d and 2d seismic data demonstrates that there is a poor spatial relationship between the two furthermore virtually all the reflector offsets directly beneath the mounds which have previously been interpreted as faults can be attributed to seismic artefacts such as velocity pull ups and diffraction cones therefore our findings strongly suggest that seismically mappable faults do not play a pivotal role as conductive fractures in the evolution of the mounds however mounds located towards the nw margin of the porcupine basin are underlain by a shallow intensely faulted slide package which provides one potential association between faults and mounds

stress variability and brittle tectonic structures the problem of stress variability both in space and time during brittle deformation of rocks is faced in this note several possible causes of the temporal and spatial variations of the stress tensor are reviewed and discussed a genetic partitioning of the stress tensor is proposed showing that any stress field within a crustal volume can be seen as the sum of relatively simple stress tensors associated to specific genetic components the genetic components discussed in this note are the gravitational the tectonic the fluid the thermal and the diagenetic one each genetic component is a function of several parameters but for all of them the possible important role played by the variable time is emphasised according to numerous researches based on theoretical and experimental grounds brittle deformation in a rock mass occurs when some critical conditions are reached starting from initial equilibrium conditions and leading to even different stress conditions as a consequence of failure field examples are presented and data from literature are discussed to exhibit evidences from complex tectonic structures and to argue about small and large scale spatial variations as well as about short and long term temporal variations of the stress trajectories and of the stress magnitudes that continuously occur during a brittle deformational event the relationships between local and temporal stress variations and what is commonly defined the regional stress field are discussed adding recommendations for future researches

great plains polygonal fault system as expressed in saskatchewan late cretaceous fault initiation and graben formation an extensive polygonal fault system pfs has been recognized in fine grained late cretaceous sediments of the western interior seaway of north america polygonal fault systems are pervasive organizations of nontectonic faults with fault traces that coalesce to form distinctive polygonal fault patterns interpretation of a three dimensional seismic dataset from southeast saskatchewan provides insight into fault initiation timing and geometry for the great plains pfs gppfs faulting initiates in the niobrara formation with the largest fault throws occurring over early cretaceous viking formation sandstone accumulations suggesting that drape compaction over the channel sand initiated some of the faulting above this faulting increases in vertical offset and the predominant fault strike angles change in the lea park belly river and bearpaw formations all homotaxial to the pierre shale throughout campanian time by late bearpaw time the initially almost random fault strike orientations change to well defined northwest southeast and west east striking grabens these grabens have up to 20 m of throw and can be 125 m wide and 900 m long at 400 m current depth predominant graben faults are the continuation of some of the deeper pfs faults moreover the grabens are present over a campanian clinoform bed and may be interpreted to indicate bearpaw time extension tectonics that is local or regional in scale the pfs helps to explain near surface faulting observed in late cretaceous sediments in the western interior seaway and could be used as a model to help explain late cretaceous geology subsurface groundwater flow and shallow natural gas reservoir continuity

stratigraphic development of the south voring margin mid norway since early cenozoic time and its influence on subsurface fluid flow abstract the cenozoic seismic stratigraphy and geological development of the south voring margin are analyzed to understand their relation to fluid flow and margin stability the regional stratigraphy and palaeomorphology of the more and voring basins indicate gradual changes in depositional environment and tectonic compression between 55 ma to 2 8 ma during brygge and kai periods and abrupt changes associated with glacial interglacial cycles from last 2 8 ma during naust period these changes resulted in deposition of various types of sediments and led to processes such as polygonal faulting and dewatering inter fingering of contouritic stratified and glacigenic sediments and margin progradation a gas hydrate related bottom simulating reflector bsr occurs at nyegga and within the central voring basin while pockmarks are observed at nyegga only diagentic reflectors due to opal a opal ct conversion dbsrs occur along a wider area beyond the shelf edge the dbsrs are located in oozes within the kai and late brygge formations the gas hydrate bsr occurrence is concentrated above eocene depocenters in hemipelagic and contouritic sediments deposited during late plio pleistocene the bsr overlies polygonal faults and dbsrs but are confined to the slope of anticlines indicating its formation being related to fluid pathways from methanogenic rocks through focused fluid flow microbial gas production in kai brygge and deeper formations may have supplied the gas for gas hydrate formation fluid expulsion due to dbsr formation and polygonal faulting in oozes may have created overpressure development in permeable layers belonging to the overlying naust formation slide headwalls are also located close to the anticlines in the study area implying that over pressured oozes and focussed fluid flow may have been important in creating weak surfaces in the overlying naust sediments promoting conditions for failures to occur

s waves profiles from noise cross correlation at small scale abstract cross correlations of ambient seismic noise recordings are studied to infer shear wave velocities vs profiles versus depth experiments are performed over inter station distances ranging from 60 m to about 400 m in the crowded and noisy historical centre of napoli where the conditions for the use of active controlled source seismic spreadings are prohibitive even for just one receiver from the noise cross correlation group velocity dispersion curves are extracted with ftan method and their non linear inversion supplies vs profiles versus depth the information of nearby stratigraphies and the range of vs variability for samples of neapolitan soils and rocks confirms the validity and reliability of the results obtained with our expeditious procedure if successfully tested in other geological settings the proposed approach is a low cost methodology to get reliable vs velocity profiles versus depth

body wave reconstruction from ambient seismic noise correlations in an underground mine abstractthe reconstruction of seismic green s functions from correlations of ambient seismic noise has recently developed as a promising approach for exploring the earth s interiors without the requirement of costly active seismic sources this approach is widely used for imaging the crust at a kilometer scale however few studies report noise based green s function reconstruction at smaller scales in industrial environments we have investigated the possibility of constructing seismic green s functions between sensors in an active underground mine garpenberg sweden by crosscorrelating seismic noise generated by mining activities we have determined with realistic numerical simulations that the mining excavations in an underground mine lead to a regime of strong scattering which is favorable for constructing seismic green s functions by crosscorrelating seismic noise one month of continuous data was recorded by 18 seismic sensors located more than 1 km below surface a variety of broadband 10 3000

pliocene paleoenvironment evolution as interpreted from 3d seismic data in the southern north sea dutch offshore sector a high resolution 3d seismic survey from the dutch offshore sector has been interpreted and subsequently correlated with existing regional seismo stratigraphic concepts derived from conventional 2d seismic data sets the interpreted 13 seismic units have been related to a newly established chrono stratigraphic framework kuhlmann et al 2006a b chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 integrated chronostratigraphy of the pliocene pleistocene interval and its relation to the regional stratigraphical stages in the southern north sea region netherlands journal of geosciences geologie en mijnbouw 85 1 19 35 resulting in up dated age control for the seismic units the generation of amplitude maps time slices and isopach maps from the 3d seismic data enabled detailed spatial and temporal reconstruction regarding the paleoenvironmental and climatological development as depicted by kuhlmann et al 2006a chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 the lowermost seismic units s1 s4 comprise condensed middle miocene to piacencian sediments deposited under warm open marine conditions these sediments show a uniform seismic facies of low amplitude reflectors the boundary of seismic unit s4 s5 around 2 6 ma delineates a shift towards generally colder climate conditions that are connected to the onset of northern hemisphere glaciation seismic unit s5 includes alternations of warmer and colder periods during warmer periods bottom currents generated elongated structures 2 5 4 km long 300 500 m wide on the horizon display these layers show as well shallow gas accumulations with a more regional extent and are related to coarser grained sediments sealed by clayey sediments of the cold phases a homogenous seismic facies is characteristic for the colder periods within seismic units s6 and s7 internal fore set structures display the regressional trend related to the cooling of this interval seismic units s8 s11 display a pattern of unoriented lineaments which was probably caused by icebergs drifting into the north sea and souring the sea floor this finding is in accordance with the shallow marine arctic conditions of this interval within these units a bright spot of 3 by 7 km in size is interpreted to result from shallow gas accumulation related to a grounded iceberg this feature represents another more local area of gas accumulation that is closely related to iceberg activity within the study area the uppermost seismic units s12 and s13 belong to a fluvial paralic paleo environment that is characterised by aggradational seismic reflectors pleistocene glacial valleys were recognised in the upper 200 m below sea floor 2007 elsevier ltd all rights reserved

fluid flow features in hydrocarbon plumbing systems what do they tell us about the basin evolution abstract fluid flow features such as sandstone intrusions mud volcano systems and pockmarks represent well known geological structures generated due to flow of fluids in the subsurface however the integration of fluid flow features in quantitative and qualitative basin analysis is still in its infancy this study presents a review and a qualitative integration of fluid flow features in basin analysis of the danish north sea area and of salt mini basins offshore angola based on results from six case studies focusing on the detection mapping and evaluation of features related to focused fluid flow in these areas in the study the diversity of seismically imaged fluid flow features in hydrocarbon plumbing systems is reviewed and their utility is demonstrated this is done by focusing on the aspects of fluid flow related features that can be integrated into basin analysis studies and how these may help us increase the understanding of basin evolution and to achieve the major goals of basin analysis such as understanding the depositional and tectonic context of the basin and the presence and extent of hydrocarbons particularly concerning the determination of fluid flow timing triggers sources and routes fluid flow features represent a major but underused tool in basin analysis

exploring the continental shelf for low geological risk nuclear waste repository sites using petroleum industry databases a uk case study abstract site selection for deep disposal of intermediate and high level radioactive waste in the uk to date has not taken full advantage of oil industry databases that cover offshore areas the shallow water area of the uk continental shelf is twice that of the onshore area and due to variations in regional geology many geological settings occur that are not found onshore the geology and hydrogeology of the uk continental shelf contrast in many respects with that of onshore areas the geology of the north sea in particular is constrained by over 3000 deep 2 km exploration wells 50 000 km 2 of 3d seismic data and several million line kilometres of 2d seismic data vastly more than the coverage of data constraining the deep geology onshore combined with detailed studies of oil and gas fields this data has led to a greater technical understanding of many aspects of offshore geology relative to that onshore these data represent an original investment of 20bn by oil and gas companies but are now in the public domain these databases are used here to compare onshore and offshore settings in terms of criteria such as structural geology fault activity and uplift subsidence clear differences emerge such as risk of seismicity exhumation and the variety of hydrogeological systems the distribution and geometry of candidate repository sites throughout the north sea salt structures shale basins sealed sandstone reservoirs and basement highs are illustrated several lines of petroleum related research have yielded lessons that may be useful in assessing deep repository locations such as migration of hydrocarbons through shale seals the exceptional combination of seismic data and well control means that offshore areas on the continental shelf and the north sea in particular can now be thoroughly explored in this context and contribute candidate sites into a nationwide portfolio of deep geological disposal options in the event of site selection being pursued in the uk an example framework for this process is presented here

ice load induced tectonics controlled tunnel valley evolution instances from the southwestern baltic sea abstract advancing ice sheets have a strong impact on the earth s topography for example they leave behind an erosional unconformity bulldozer the underlying strata and form tunnel valleys primarily by subglacial melt water erosion and secondarily by direct glacial erosion the conceptual models of the reactivation of faults within the upper crust due to the ice sheets load are also established however this phenomenon is also rather under explored here we propose a causal link between ice load induced tectonics the generation of near vertical faults in the upper crust above an inherited deep rooted fault and the evolution of tunnel valleys the kossau tunnel valley in the southeastern bay of kiel has been surveyed by means of high resolution multi channel seismic and echosounder data it strikes almost south to north and can be mapped over a distance of ca 50 km it is 1200 8000 m wide with a valley of up to 200 m deep quaternary deposits fill the valley and cover the adjacent glaciogenic unconformity a near vertical fault system with an apparent dip angle of 80 which reaches from the top zechstein upwards into the quaternary underlies the valley the fault partially pierces the seafloor and growth is observed within the uppermost quaternary strata only consequently the fault evolved in the late quaternary the fault is associated with an anticline that is between 700 and 3000 m wide and about 20 40 m high the fault anticline assemblage neither resembles any typical extensional compressional or strike slip deformation pattern nor is it related to salt tectonics based on the observed position and deformation pattern of the fault anticline assemblage we suggest that these structures formed as a consequence of the differential ice load induced tectonics above an inherited deep rooted sub salt fault related to the gluckstadt graben lateral variations in the ice load during the ice sheet s advance caused differential subsidence thus rejuvenating the deep rooted fault as a result the inherited fault propagated upwards across the zechstein and post permian overburden and further grew during the ice sheet s retreat the developing fault and anticline system under the ice sheet created a weakness zone that facilitated erosion by pressurized glacial and subglacial melt water as well as by the glaciers themselves near vertical faults cutting through the post permian are abundant in the southwestern baltic realm which implies that the ice load induced tectonic activity described above was not an isolated incident

can polygonal faults help locate deep water reservoirs polygonal faults are compaction related normal faults that develop in very fine grained sedimentary successions despite their ubiquity few studies have highlighted the application of polygonal fault mapping to identifying deep water sandstone reservoirs we use three dimensional seismic and borehole data from the maloy slope offshore norway to demonstrate that the distribution cross sectional geometry and throw characteristics of polygonal faults can be used to locate deep water sandstone reservoirs we identify two tiers of polygonal faults in the cretaceous to lower paleogene succession the lowermost tier is stratigraphically restricted to the lower barremian to lowermost turonian succession and likely formed during the early turonian the uppermost tier spans the entire cretaceous succession and likely formed during the maastrichtian an abrupt decrease in the thickness of the upper tier occurs where a 92 m 302 ft thick sandstone rich slope fan is developed in the upper turonian interval furthermore the lower tips of faults in the upper tier which are defined by anomalously high throw gradients cluster at the top of the sandstone resulting in decoupling of this tier from the underlying lower turonian tier we interpret that faults in the upper tier nucleated above the reservoir across the entire slope and that the slope fan sandstone acted as a mechanical barrier to downward fault propagation resulting in abrupt thinning of the tier at the sandstone pinchout we demonstrate polygonal faults are not simply an academic curiosity mapping of these enigmatic structures can have practical applications for the delineation of a variety of reservoir types in hydrocarbon bearing sedimentary basins worldwide

3d s wave velocity imaging of a subsurface disturbed by mining using ambient seismic noise abstract seismic interferometry based on ambient seismic noise was used to image the 3d s wave velocity field of a subsurface disturbed by mining under the geological conditions at the kghm rudna copper mine in southwestern poland we recorded ambient seismic noise data for 3 months using 11 surface mounted broadband seismometers located across the mining area we used ambient noise cross correlation techniques to create a three dimensional s wave velocity model of the cenozoic and triassic formations up to a depth of 500 m cross correlation functions ccfs indicate the rayleigh and love waves however only the love waves in the 0 19 0 4 hz frequency range were reliable based on the symmetry of the ccfs in the positive and negative conditions imaging using the love waves indicated that the changes in the s wave velocity field in the model may be explained by the subsidence processes occurring above the mined area the s wave velocity decreased above the areas of the current mining operations however the s wave velocity increased above older mined areas probably due to suppression of the subsidence process and progressive consolidation of the geological medium over time we also observed low velocity anomalies in the intersection zones of the larger faults with high energy seismic events this could be caused by fault activation by current mining operations and a reduction in the stiffness of the layers in the fault intersection zone this study presents the possibility of imaging the subsurface layers in a mining area using ambient seismic noise it also has the potential to give a broader insight into how a geological medium responds to mining in terms of protecting the terrain surface and developing mining technologies

seismic evidence for repeated vertical fluid flow through polygonally faulted strata in the canterbury basin new zealand abstract seismic imaging techniques are widely used to determine fluid migration pathways in the subsurface understanding the timing and distribution of focused fluid migration pathways is important for assessing reservoir seal quality and hydrocarbon exploration risk as well as seafloor biogeochemical processes in the case of fluid venting from the seafloor the frontier canterbury basin southeast of new zealand is well studied but questions remain regarding the dynamic movement of fluids through the basin using 3d seismic data combined with high resolution boomer seismic data we characterise focused fluid migration and sediment remobilisation events in the canterbury basin we show how polygonal fault formation and nucleation is affected in the vicinity of vertically ascending fluids and sediments a cylindrical region devoid of polygonal faulting around the feeder system of a buried sediment volcano points to the possible existence of an axisymmetrical stress field induced by upward migrating fluids and sediments sediment remobilisation and intrusions of permeable stingers i e sand injectites could enable dewatering of their host strata and thereby prevent polygonal faults from nucleating amplitude variations with angle ava and a detailed analysis of two tiers of polygonal faults reveal three phases of fluid migration and sediment remobilisation and intrusion through and into low permeability sediments our integrated conceptual model provides insights into vertical fluid migration mechanisms and the implications for polygonal fault formation

hydraulic resistance of flow in channels with cylindrical roughness a laboratory study on the hydraulics of flow in an open channel with circular cylindrical roughness is presented the laboratory study consists of an extensive set of flume experiments for flows with emergent and submerged cylindrical stems of various sizes and concentrations the results show that the flow resistance varies with flow depth stem concentration stem length and stem diameter the stem resistance experienced by the flow through the vegetation is best expressed in terms of the maximum depth averaged velocity between the stems physically based formulas for flow resistance the apparent channel velocity and flow velocities in the roughness and surface layers are developed the formulas are validated with the flume data from the present study as well as those from past studies a method for calculating channel hydraulic conditions using these formulas is presented

an experimental study of flow through rigid vegetation 1 better understanding of the role of vegetation in the transport of fluid and pollutants requires improved knowledge of the detailed flow structure within the vegetation instead of spatial averaging this study uses discrete measurements at multiple locations within the canopy to develop velocity and turbulence intensity profiles and observe the changes in the flow characteristics as water travels through a vegetation array simulated by rigid dowels velocity data was collected with a one dimensional laser doppler velocimeter under emergent and submerged flow conditions the effects of dowel arrangement density and roughness were also examined the results show that the velocity within the vegetation array is constant with depth and the velocity profile is logarithmic above it however the boundaries are marked by inflection points the strongest vortices and turbulence intensities can be found there especially in the region immediately downstream of a dowel these results support the idea that the flow in the region near the bed and at the top of the dowel array is very unstable leading to the formation of coherent structures and are areas of significant mass and momentum exchange

analytical solution of the depth averaged flow velocity in case of submerged rigid cylindrical vegetation a new model for the depth averaged velocity for flow in presence of submerged vegetation is developed the model is based on a two layer approach where flow above and through the vegetation layer is described separately vegetation is treated as a homogeneous field of identical cylindrical stems and the flow field is considered stationary and uniform it is demonstrated that scaling considerations of the bulk flow field can be used to avoid complications associated with smaller scale flow processes and that still the behavior of depth averaged flow over vegetation is described accurately the derived scaling expression of the average flow field is simple in form it follows fundamental laws of fluid flow and it shows very good agreement with laboratory flume experiments the new model can be used for quick evaluation of a river s hydraulic response in cases where vegetated floodplains are inundated

the interdisciplinary use of overpressure abstract overpressure is a polysemic word that has a variety of meanings within and across different disciplines this is likely to be a particular problem in analysis of geothermal resources where reservoir engineers volcanologists and structural geologists may each confidently use overpressure but mean different things we suggest that to avoid confusion the term should be carefully and accurately defined whenever used and ideally only used to mean fluid pressure in excess of hydrostatic pressure

a typical evolution of seismicity patterns resulting from the coupled natural human induced and coseismic stresses in a longwall coal mining environment abstract a very unusual time space distribution of seismicity accompanying coal exploitation has been observed in a polish mine the earthquakes did not follow the depth of mining but exhibited changing depths from far below to close to the mined seam one of the deep events which occurred at close epicentral distance to the active mining front was m l 3 7 event this paper presents the study of possible coupling of natural human induced and coseismic stresses in a longwall coal mining environment the full moment tensor solution showed that the strong earthquake occurred on an almost vertical plane consistent with approximate strike of local tectonic structure the signal correlation analysis revealed some highly correlated pairs within both deep and shallow event groups to evaluate inducing factor of ongoing and past exploitation geomechanical modelling of its influence on strain and stress at the target depth has been performed the results exhibited a changing vertical stress regime which might have promoted failure on preexisting almost vertical planes of weakness the earthquakes rate variation in time showed no increase in activity right after the occurrence of m l 3 7 event the p s wave spectra corner frequency ratio had an average of 1 0 suggesting slow rupture however the coulomb stress change analysis showed that the magnitude of stress changes due to coseismic slip of m l 3 7 event at the hypocentral depth is of the same order as the stress changes caused by mining thus the distribution of seismicity at this level could have been driven by both exploitation and coseismic stresses moreover the seismicity which occurred within first few weeks after m l 3 7 event followed positive stress changes all the obtained results let us prove that the m l 3 7 event was a tectonic earthquake triggered by ongoing exploitation and that the distribution of following seismicity was affected by coupled natural exploitation induced and coseismic stresses

discussion on geometry and origin of a polygonal fault system journal vol 157 2000 151 162 scientific editing by richard england d m d james writes the paper is much to be welcomed as bringing new and stimulating ideas to the ongoing debate concerning the origin of polygonal faults cartwright lonergan 1996 cartwright dewhurst 1998 however if the proposed mechanism of blind faulting above sites of incipient diapirism is correct then demonstration is required of significant thickness variation of the causative mobile layer and of a density inversion across its upper boundary the following remarks aim largely to seek geophysical reassurance on these aspects and as such are also relevant to many of the increasing number of journal papers that utilize seismic and well data from the oil and gas industry the candidate mobile layer is stated to be a shale fortuitously preserved at its depositional thickness of 35 m in the only control well apparently available it is critical for the authors interpretation fig 8b that both top and bottom of this shale are mappable seismically and the character of the sonic log fig 1c gives some encouragement that this may indeed be possible ideally via an exact tie to the well based on a well shoot an acoustic impedance profile from well logs and knowledge of the phase and polarity of the seismic no such tie is mentioned but assuming that the position of the shale is approximately as shown in fig 3a rather than its accompanying rather obvious seismic mistie in fig 3b the distinctive and rather tram line character at this level makes it very difficult to accept the authors requirement of a range of mobile thicknesses of 0 70 m pp 156 160 such variation should easily be resolvable and the extreme thinning indicated by tuning effects at the likely seismic bandwidth seismic lines illustrated as figs 6b d

seismic characterization of a highly stressed rock mass using tomographic imaging and induced seismicity a seismic tomography study was carried out at falconbridge s lockerby mine sudbury canada in april 1989 the objective was to determine the integrity of a rock mass at 1 km depth and to investigate the correlation between induced seismicity and p wave velocity structure the tomographic image showed two distinct and significant p wave velocity anomalies a low velocity zone at the source region of a mn 2 3 mining induced tremor recorded in 1985 and a high velocity zone at the source region of a mn 2 6 mining induced tremor recorded in 1988 analysis of mining induced microseismicity showed that the high velocity zone was the focus for seismic activity prior to and after the 1988 tremor in contrast to the low velocity zone which remained aseismic for the same period the seismic anomalies were diamond drilled following the tomographic imaging to verify the physical characteristics of the zones the seismically active high velocity zone showed severe core disking indicative of a highly stressed strong rock while the low velocity zone was characterized by extensive fracturing and failed rock the results showed that the 1985 tremor and rock burst sequence resulted in a major failure of the rock mass in the source region of the event and stress was redistributed and concentrated in the source region of the 1988 tremor the 1988 event and rock burst sequence did not result in failure of the source region which therefore remains a seismically active high velocity zone with a potential for significant seismic energy release and further rock bursting the study has highlighted a correlation between p wave velocity structure and induced seismicity which can be used to characterize highly stressed rock masses in underground mines

episodic basin wide hydrofracturing of overpressured early cenozoic mudrock sequences in the north sea basin a deformational fabric associated with the early cenozoic mudrock dominated sequences of the north sea is described seismic data show that the mudrock sequences are pervasively faulted over a large area of the basin axis in the central and northern north sea mapping the faults using regional two and three dimensional data shows that the faults are minor extensional structures arranged in stratigraphically bound tiers in the deep water sequences and bounded by regional condensed sequences seals the geometry of the faulting is complex faults are organized into cellular networks comprising polygonal prismatic and pyramidal forms a gravitational mechanism of downslope collapse faulting is rejected on the grounds that the distribution of the deformed sequences extends over large areas of formerly horizontal basin plain a mechanism involving the repeated development of basin wide overpressured compartments is proposed in which the cellular structure is related to deformation patterns associated with a density inversion between the overpressured units and the overlying seal hydrofracturing is invoked to account for the almost random strike distribution of the faulting the region affected by the pervasive fluid expulsion faulting encompasses almost half of the north sea basin basin wide collapse of the overpressured compartments could have resulted in a geologically rapid flux of enormous volumes of pore fluids this mechanism has implications for concepts of steady state compaction heat flow in basins hydrocarbon transport and the genesis of lead zinc ore deposits