induced earthquakes at a potash mine near saskatoon canada four earthquakes with magnitudes between 2 3 and 3 0 which occurred between november 1979 and august 1980 are correlated with a potash mining operation near saskatoon previous seismicity in the region is unknown detailed intensity surveys constrain the epicentres over or close to the periphery of the underground mining excavations from microearthquake recordings over the mine and from an analysis of short period surface waves recorded for the march 18 event focal depths are constrained to the region above the excavation microearthquakes show both temporal and spatial correlations with the mining activity the results indicate that the relatively competent carbonate rock above the mine is spasmodically undergoing brittle failure or sudden rupture presumably normal faulting due to induced changes in the local stress strain regime as a result of the mining excavation and the accompanying subsidence in the mine overburden

geophysical evaluation of effectiveness of blasting for roof caving during longwall mining of coal seam deep longwall mining of coal seams is made in the upper silesian coal basin uscb under complicated and mostly unfavourable geological and mining conditions usually it is correlated with rockburst hazard mostly at a high level one of the geological factors affecting the state of rockburst hazard is the presence of competent rocks in the roof of extracted coal seams so rock falling behind the longwall face does not occur and hanging up of roof rocks remains the long lasting absence of caving may lead to an occurrence of high energy tremor in the vicinity of the longwall face roof caving behind the longwall face may be forced by blasting the column of explosives is then located in blastholes drilled in layers of roof rocks e g sandstones behind the longwall face in this article a characterization of tremors initiated by blasts for roof caving during underground extraction of coal seam no 507 in one of the collieries in the uscb has been made using three independent methods by the basic seismic effect method the effectiveness of blasting is evaluated according to the seismic energy of incited tremors and mass of explosives used according to this method selected blasts gave extremely good or excellent effect an inversion of the seismic moment tensor enables determining the processes happening in the source of tremors in the foci of provoked tremors the slip mechanism dominated or was clearly distinguished the expected explosion had lesser significance or was not present by the seismic source parameters analysis among other things an estimation of the stress drop in the focus or its size may be determined the stress drop in the foci of provoked tremors was in the order of 105 pa and the source radius according to the brune s model varied from 44 3 to 64 5 m the results of the three mentioned methods were compared with each other and observations in situ in all cases the roof falling was forced

source mechanism of mining induced seismic events resolution of double couple and non double couple models abstract traditional assumption about a seismic source as a double couple dc can represent a serious limitation for describing mechanisms of mining induced seismic events in mining conditions more general process than a shear slip can occur due to stress concentration on mined out areas we assume both non dc components within the dipole description of the source the moment tensor and a single force we processed five seismic events recorded at driefontein gold mine in south africa to demonstrate that waveform modeling is not successful enough due to poor information about the medium inversion of amplitudes of direct p and s waves is more prospective due to their smaller sensitivity to detail of the medium and possibility to correct them for ray bending and shear wave splitting prior to the inversion moreover we are able to estimate the error of the resulting mechanism due to neglect of ray bending all five events processed display non dc mechanisms which are significant at 95 considering the mismodelling of the rock mass by a homogeneous isotropic medium the source mechanisms are in agreement with the underground mining and geological structures one event has a sub vertical pressure single dipole complemented by an implosion which is the body force equivalent of a collapsing horizontal crack or a burst of a pillar supporting the hangingwall of a mined out area two events have mechanisms close to a pressure single couple all three events are located on pillars two out of these three events can be assigned with a downward single force as an alternative mechanism which matches the amplitude data successfully it is the force equivalent of a mined out area collapse when a rock mass falls from the hangingwall to the footwall the events are however rather strong which would require too large rock mass fallen one of the remaining events is a nearly horizontal tensile single couple corresponding to a vertical tensional fault it could be originated by a break of the hangingwall of a mined out area however the hypocenter of this event is deep into the footwall were there is no mining taking place the last event is mostly dc accompanied by a compensated compressive dipole which may be associated to nearly vertical dip slip along a fault in the hangingwall this event is located on the margin of a wide pillar which supports the interpretation

suspended sediment concentration and calibre in relation to surface flow structure in squamish river estuary southwestern british columbia surface grabs of suspended sediments from boils and the background flow in squamish estuary revealed strong differences between the two environments boils exhibit higher sediment concentrations and larger particle sizes than the background flow the higher sediment concentrations and larger grain sizes in boils are related to tidal phase with maximum concentrations and sediment sizes occurring in the early decelerating phase of the tidal flow sediment concentrations and grain sizes in the background flow are comparatively invariant with tidal phase boils appear to play an important if not dominant role in suspending and transporting sand sized sediments in squamish estuary

induced seismicity in mines in canada an overview monitoring of mine induced seismicity in canada has improved with the expansion of regional seismograph networks into areas of active mining however the severity and in some cases the frequency of mine induced tremors has increased as mining extends to greater depths and at accelerated rates of extraction because of the complex design and large areal extent of many mines potash coal and metalliferous the most feasible and practical way to monitor these tremors at the present time is to deploy a network of seismometers in and on the surface above mines experiencing microearthquake activity a few of these mines already have a network of seismometers deployed around them and plans are under way to deploy seismograph networks around other mines that have experienced some rather severe tremors in recent times six possible mechanisms for mine induced tremors are described and the associated p and s wave radiation patterns presented a comparison of actual seismic radiation patterns with theoretical predictions is a quick way to diagnose the potential source mechanisms in addition recognizing the pattern of microearthquake activity preceding larger tremors can be used to mitigate the potential effects of severe tremors

moment tensor inversion of regional phases application to a mine collapse the aim of our study consists of analyzing potentially non double couple seismic events recorded at regional distances in order to define the nature of the seismic source a moment tensor inversion is carried out as this method is general enough not to initially constrain the source mechanism in this paper we present an application to a seismic event induced by a mine collapse which occurred near the town of halle in germany because of its induced nature many parameters such as the location and geometry of this seismic source are known this information allows us to test the influence of inadequate propagation modeling on the moment tensor obtained from the inversion green s functions have been computed with the reflectivity method in a flat layered medium using the european model eurid du et al 1998 dufumier et al 1997 from the inversion of p wave seismograms recorded by the german regional seismic network will we obtained a source time function which can be decomposed into two subevents the first one has a large isotropic part and a deviatoric mechanism with near vertical nodal planes no volume change is observed for the second subevent but a deviatoric component opposite of the first one the addition of s waves does not change the results of the inversion which are stable surface waves were not used because of their poor dispersion curves based on the moment tensor obtained from these inversions the physical process at the source is compatible with a large cavity collapse

morphodynamics of small scale superimposed sand waves over migrating dune bed forms 1 the kinematics and morphodynamics of low amplitude small scale sand waves developed over migrating dunes are examined using data drawn from laboratory experiments we refer to the superimposed features as sand sheets a general descriptive term for low amplitude bed waves that are not easily classified as ripples dunes or bars within the experiments the sheets formed downstream of the reattachment point at a distance that was invariant with dune size some sheets lacked slip faces composed of sand grains avalanching down a slope near the angle of repose over equilibrium dunes three to four sand sheets were observed per 100 s sheet thickness was 10 of the height of the dune upon which they were superimposed they migrated at 8 to 10 times the dune rate they had nearly constant lengths over the full range of dune lengths and flow conditions and they had aspect ratios of 0 025 dunes and sand sheets represent distinct scales of sediment transport with different migration rates however sediment transport rates calculated from the sand sheet and dune morphologies are nearly identical for transport equivalence to occur sand sheets migrating at 10 times the dune rate must be 0 1 times the size which is consistent with the morphological observations superimposed bed waves on dunes are often considered simply as additional roughness elements but these results indicate that such bed waves are the agency by which the dune bed form itself moves downstream

correlations between mining and seismicity for re entry protocol development abstract re entry protocols are a strategic approach for controlling risk after large magnitude events or blasts in seismically active mines by monitoring the return of seismicity to background levels restricting access to areas of a mine affected by seismicity for sufficient time to allow this decay to occur is the main approach in most re entry protocols in the present study mining and seismicity are correlated for re entry protocol development by using a uniform statistical technique for the identification of background levels the relations are established relying on a theoretical framework that links the productivity of seismicity with the decay time of seismic sequences three case histories are presented and analyzed selected to illustrate the possible effects of factors such as volume of mined rock depth and magnitude of large events on the decay time of mining induced seismic sequences positive significant correlations between the decay time and the mining factors studied here are found

large eddy simulation of sediment transport currents over ripples a large eddy simulation has been performed to study the detailed sediment dynamics that occur in channel flow over ripples the code solves the navier stokes equations and an advection diffusion equation for the sediment and has been verified to produce quantitatively accurate hydrodynamic results for the flow domains used in this study the main features of interest in this flow are seen because of the high resolution of the grid especially near the ripple boundary this yields a detailed bottom shear stress distribution properly identified coherent structures and resolved sharp gradients in the sediment concentration globally the sediment is carried up into the flow from locations where the shear stress is high on the upslopes of ripple crests and is advected downstream by the current and upward by the vertical velocity component regions of positive vertical velocity are associated with gortler vortices which represent a significant sediment transport mechanism in this flow

rock mass characterization around saskatchewan potash mine openings using geophysical techniques a review saskatchewan potash deposits are found in relatively uniform flat bedded strata with few irregularities potash mines are highly automated and efficient taking advantage of the uniform strata ho

automated full moment tensor inversion of coal mining induced seismicity seismicity induced by coal mining in the ruhr region germany has been monitored continuously over the last 25 yr in 2006 a dense temporary network hamnet was deployed to locally monitor seismicity induced by longwall mining close to the town of hamm between 2006 july and 2007 july more than 7000 events with magnitudes m l from 1 7 to 2 0 were detected the spatiotemporal distribution of seismicity shows high correlation with the mining activity in order to monitor rupture processes we set up an automated source inversion routine and successfully perform double couple and full moment tensor mt inversions for more than 1000 events with magnitudes above m l 0 5 the source inversion is based on a full waveform approach both in the frequency and in the time domain providing information about the centroid location focal mechanism scalar moment and full mt inversion results indicate a strong dominance of normal faulting focal mechanisms with a steeper plane and a subhorizontal one fault planes are oriented parallel to the mining stopes we classify the focal mechanisms based on their orientation and observe different frequency magnitude distributions for families of events with different focal mechanisms the overall frequency magnitude distribution is not fitting the gutenberg richter relation full mts indicate that non negligible opening tensile components accompanied normal faulting source mechanisms finally extended source models are investigated for largest events results suggest that the rupture processes mostly occurred along the subvertical planes

changes in mining induced seismicity before and after the 2007 crandall canyon mine collapse on 6 august 2007 the crandall canyon mine in central utah experienced a major collapse that was recorded as an mw 4 1 seismic event application of waveform cross correlation detection techniques to data recorded at permanent seismic stations located within 30 km of the mine has resulted in the discovery of 1494 previously unknown microseismic events related to the collapse these events occurred between 26 july 2007 and 19 august 2007 and were detected with a magnitude threshold of completeness of 0 0 about 1 6 magnitude units smaller than the threshold associated with conventional techniques relative locations for the events were determined using a double difference approach that incorporated absolute and differential arrival times absolute locations were determined using ground truth reported in mine logbooks lineations apparent in the newly detected events have strikes similar to those of known vertical joints in the mine region which may have played a role in the collapse prior to the collapse seismicity occurred mostly in close proximity to active mining though several distinct seismogenic hot spots within the mine were also apparent in the 48 h before the collapse changes in b value and event locations were observed the collapse appears to have occurred when the migrating seismicity associated with direct mining activity intersected one of the areas identified as a seismic hot spot following the collapse b values decreased and seismicity clustered farther to the east

rip currents mega cusps and eroding dunes abstract dune erosion is shown to occur at the embayment of beach mega cusps o 200 m alongshore that are associated with rip currents the beach is the narrowest at the embayment of the mega cusps allowing the swash of large storm waves coincident with high tides to reach the toe of the dune to undercut the dune and to cause dune erosion field measurements of dune beach and rip current morphology are acquired along an 18 km shoreline in southern monterey bay california this section of the bay consists of a sandy shoreline backed by extensive dunes rising to heights exceeding 40 m there is a large increase in wave height going from small wave heights in the shadow of a headland to the center of the bay where convergence of waves owing to refraction over the monterey bay submarine canyon results in larger wave heights the large alongshore gradient in wave height results in a concomitant alongshore gradient in morphodynamic scale the strongly refracted waves and narrow bay aperture result in near normal wave incidence resulting in well developed persistent rip currents along the entire shoreline the alongshore variations of the cuspate shoreline are found significantly correlated with the alongshore variations in rip spacing at 95 confidence the alongshore variations of the volume of dune erosion are found significantly correlated with alongshore variations of the cuspate shoreline at 95 confidence therefore it is concluded the mega cusps are associated with rip currents and that the location of dune erosion is associated with the embayment of the mega cusp

rock mechanical investigations of seismic events in a deep longwall coal mine seismic events i e fractures in rock that radiate detectable seismic waves are a worldwide phenomena associated with mining and reservoir exploitation longwall mining in german coal mines often causes seismic events which can be felt at surface where they can lead to a considerable annoyance of residents and sometimes even lead to minor damages of buildings and infrastructure strong seismic events are in a large part responsible for a more and more decreasing community acceptance of mining the mines therefore have to investigate the local conditions which cause the generation of seismic events to find ways of avoiding strong mining induced seismic events this paper describes the research on mining induced seismicity around a specific active longwall at 1100 m depth under several previously mined longwall panels seismic events are recorded by a local network featuring 15 surface and six subsurface stations location and fault plane solutions show the occurrence of at least three different event types which are characterized by distinct modes of failure underground core drilling and an extensive rock testing program are used to build up a rock mechanical model featuring a multi layer strata for use with numerical analyses the numerical model is able to explain the different failure mechanisms as fault activation remnant pillar punching and beam failure the use of rock mass classification rock mass strength criteria and in situ stresses together with 2d and 3d numerical analyses facilitates the evaluation of the results from seismology approaches and makes future analysis of longwall related seismic events possible

rock mechanics analysis of the springhill mine disaster october 23 1958 abstract the evolution of mining practices in the collieries at springhill nova scotia is recounted over a 40 year period during which 525 bumps or rock bursts were recorded in the no 2 mine where mining progressed to a depth of over 4000 feet at this depth a devastating bump occurred which destroyed the whole of the producing area of the mine early rock mechanics studies undertaken by the fuels division of the department of mines and technical surveys during the five year period prior to the disaster are described and a re assessment is made of some of the data the displacement discontinuity method of stress analysis for tabular ore bodies is used to study patterns of stress build up during the mining of the last three longwalls factors contributing to bumping are discussed and a theory of bump mechanism is developed in the light of descriptions of earlier bumps at springhill and literature from other bump and rock burst prone areas of the world bumping in coal mines appears to be inevitable under certain conditions of depth and geology better understanding of the mechanism of bumps permits the design of more effective counter measures to mitigate the hazards from bumping micro seismic monitoring seems to be the most promising method of early warning of bump occurrences

aftershocks of an explosively induced mine collapse at white pine michigan abstract we recorded an explosively induced 320 m deep mine collapse and subsequent aftershocks at white pine michigan using an array of 12 seismic stations sited within 1 km of surface ground zero the collapse which followed the rubblizing of a 2 10 4 m 2 panel of a room and pillar copper mine was induced to facilitate leaching operations the explosions produced little seismic energy however fracturing and collapse stages produced large signals that were observed at distances up to 900 km yielding a magnitude m blg of 2 8 previous work showed the initial collapse to be an expanding seismic source interpreted as an opening tensile crack opposite to the implosional character most often observed for natural mine collapses yang et al 1998 we counted over 4000 aftershocks their occurrence rate followed the modified omori law rate 560 time 0 01 1 3 with time in hours based on p wave polarities we identified events of shear slip implosional and tensile character in the aftershock sequence for shear slip events we found stress drops of 1 bar or less seismic moments of 10 15 10 17 dyne cm m w 0 8 0 5 and source radii of 10 50 m corner frequencies for implosional events were relatively low an indication that the collapsed cavity played a role in the source process this caused implosional events to separate from other events in source parameter plots providing a technique for classifying events of unknown type we obtained locations of 135 aftershocks using p and s wave data the aftershock zone was less than 100 m thick situated just above and along the western mined edge of the collapsed mine panel implosional events occurred at the bottom of the active volume while shear slip events were distributed throughout shear slip focal mechanisms indicated thrusting along north striking planes consistent with the high eastwest regional compressive stress coupled with a local decrease in vertical stress the inferred deficit of vertical stress above the western panel edge following collapse indicated that overburden load shifted preferentially to the surrounding unmined areas consistent with lower than predicted stresses measured in the first row of intact pillars

a re examination of the seismicity of michigan abstract according to reports on felt shocks and those recorded by instruments 105 seismic events have been reported as occurring within michigan from the 1700 s to the present of these 41 instrumental events are due to chemical explosions detonated in experiments during 1964 1966 of the remaining events most of those reported from the upper peninsula are related to mining in the lower peninsula most events can be shown or strongly inferred to be cryoseisms atmospheric shock waves from explosions or aircraft or errors in location or reporting at least four and perhaps up to eight events are thought to be tectonic earthquakes and occur in the southernmost part of the state primarily in western lake erie and the southwestern corner of the state or in lake superior this study indicates that the seismicity level within michigan is very low and that there is no evidence to substantiate either a tectonically active michigan basin seismic zone or the extension of the midcontinent seismic zone into keweenaw peninsula in addition these results suggest that earthquake catalogs for weakly seismic regions may be contaminated with non tectonic and even non seismic events thirty earthquakes occurring outside the state have also been reported in michigan these lie primarily along a line connecting the st lawrence seaway and the new madrid zone of missouri

induced seismicity and the potential for liability under u s law abstract research by seismologists over the past 30 years has firmly established that some human activities induce seismicity sometimes induced seismicity causes injuries to people or property the activities which induce seismicity generally involve extraction of energy or natural resources or the disposal of wastes as the human population increases these extraction and disposal activities will increase in number of sites and intensity of effort as the demands become greater and the resources scarcer with these increases the number and severity of damaging induced earthquakes is likely to increase induced seismicity may cause injuries by vibrations or by seismically induced ground failure in either case compensation for injuries caused by induced seismicity should be paid for by the inducer in the united states the inducer of damaging seismicity can be made to pay for the harm caused liability for damage caused by vibrations can be based on several legal theories trespass strict liability negligence and nuisance our research revealed no cases in which an appellate court has upheld or rejected the application of tort liability to an induced earthquake situation however there are numerous analogous cases that support the application of these legal theories to induced seismicity vibrations or concussions due to blasting or heavy machinery are sometimes viewed as a trespass analogous to a physical invasion in some states activities which induce earthquakes might be considered abnormally dangerous activities that require companies engaged in them to pay for injuries the quakes cause regardless of how careful the inducers were in some circumstances a court may find that an inducer was negligent in its site selection or in maintenance of the project if induced seismicity interferes with the use or enjoyment of another s land then the inducing activity may be a legal nuisance even if the seismicity causes little physical damage in most states of the united states owners of land owe a duty of lateral support to adjacent landowners and in some states mineral estate owners and lessees owe a duty of subjacent support to the surface owners failure to meet those duties of support can result in liability seismicity induced by one source might accelerate failure of support originating from another source leaving both of the parties at fault proportionally liable to the injured parties geoscientists can use their roles as investigators educators and advisors to help companies in the petroleum mining and geothermal fields avoid liability

the cqu regional seismic network and applications to underground mining in central queensland australia the central queensland university cqu regional seismic network is made up of an array of six short period seismometer and two strong motion accelerometer stations the array has an aperture of about 50 km cqu is able to resolve epicentral co ordinates to about 2 kilometres with a sample rate of 100 per second and an absolute time accuracy of 100 milliseconds this resolution is achieved by using triaxial seismometers which allow better secondary phase identification of shear converted and depth phases

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

morphological evolution and dynamics of a large sand braid bar jamuna river bangladesh the initiation and evolution of a kilometre scale sand braid bar was monitored during a 28 month survey period from 1993 to 1996 in one of the world s largest braided rivers the jamuna river bangladesh repeated bathymetric surveys through two monsoon flood seasons combined with bar top surveys during exposure of the bar at low flow provide the most detailed chronology of braid bar growth yet compiled for a large sand bed river during rising and peak flow of the 1994 monsoon flood a 1 5 km long 0 5 km wide 12 m high symmetrical mid channel bar was deposited in the centre of a major channel downstream of a zone of flow convergence and significant bank erosion initial deposition and growth of the bar core were probably caused by amalgamation of dunes that are present in the jamuna channels at all flow stages bar top aggradation continued through downstream migration of an accretionary dune front a 3 m high angle of repose slipface that was composed of amalgamated 0 5 to 1 m high dunes at waning and low flow the mid channel bar widened by up to 1 km through the lateral accretion of dunes onto the margins of the initial bar core a low velocity zone in the sheltered wake region of the bar tail led to the accumulation of substantial volumes of silts and clays during the rising and peak flows of the next monsoon flood the mid channel bar extended its bar tail by up to 1 5 km as one of the anabranches became dominant and flow was deflected across the bar tail accretion at the bar tail generated a lobate transverse bar front with a 10 m high angle of repose avalanche face emergence of several smaller bars along this depositional front produced an overall reach morphology that more closely resembled an alternate bar rather than several mid channel bars the conversion of a mid channel bar to an alternate bar is contrary to many previous descriptions of the braiding process

contribution of salinas river sand to the beaches of monterey bay california during the 1978 flood period fourier grain shape analysis abstract examination of medium grained sand from southern monterey bay using fourier grain shape analysis and q mode multivariate techniques was performed to identify the contribution of sand from the salinas river to the beaches along the bay following an episode of high stream discharge conventional textural and petrographic analyses also were used to aid in the interpretation of potential local sources for the sand in monterey bay fundamental sedimentologic properties along the littoral zone of monterey bay remained much the same during the 1978 flood period but some distortion and greater sediment mixing occurred within certain segments of the shorezone statistically significant shape differences define various potential sand sources a two factor solution which explains 91 percent of the total sample variance shows two sources represented by salinas river sand and southern beach sand adjacent to a pre flandrian and flandrian dune complex the other potential sources offshore and beach sand from north of the salinas river are mixtures of the two extracted factors offshore sand deposits in the southern bay accumulated by the seaward transport of adjacent beach sand northern beach sand which is similar n shape to salinas river sand is deposited by longshore transport of pajaro river and soquel creek sand both streams drain an area similar to that drained by the salinas river which accounts for the similarity of salinas river and northern beach sand during the 1978 flood season the contribution of salinas river sand to the southern monterey bay beaches ranged from 63 percent south of the river mouth to 0 percent near fort ord even during a period of high salinas river discharge the dominant source of the southern monterey bay beach sand is reworking of the adjacent flandrian and pre flandrian dune complex thus this sand must be considered a nonrenewable resource

mechanics of flow over ripples and dunes a simple predictive model for velocity and boundary shear stress fields over two dimensional bedforms of finite amplitude is presented herein and the results of that model are compared with flume data the production of a wake due to separation of the flow near the bedform crest and the subsequent interaction of this wake region with a developing nonuniform boundary layer downstream of the flow reattachment point are treated using the method of mclean and smith 1986 their model is modified in order to take account of the flow response to short wavelength obstructions more accurately and to include the effects of wakes from upstream bedforms as these wakes coalesce in the interior the theory is also extended to include the region between the bedform crest and the reattachment point thereby providing a spatially complete field of velocity and shear stress results of the calculations are found to be in good agreement with laboratory measurements taken over immobile bedforms using a laser doppler velocimeter our finite amplitude flow model is shown to yield accurate predictions of the fluid dynamical effects ultimately responsible for the morphology of well developed natural bedforms

seismic moment tensor resolution on a local scale simulated rockburst and mine induced seismic events in the kopanang gold mine south africa seismic records contain information about the effect of the source as well as the effect of wave propagation through the rock mass the effect of wave propagation is usually not well known as only simplified models of geological structures are available therefore the information about the source retrieved by inverting seismograms may include errors due to incomplete knowledge of the rock mass along the propagation path which in turn cause a distortion in the calculated moment tensor mt the distortion of the mt on a local scale was observed by inverting records of a simulated rockburst conducted at the kopanang gold mine in south africa a dominant isotropic component of the explosive characteristics was found from the inversion the deviatoric components retrieved from the blast are spurious a test of their stability indicated that they are not significant assuming an uncertainty above 5 for velocities and 10 for attenuation within the homogeneous model available for the mine thus the retrieval of the mt from records of local networks in mines using a homogeneous model of the rock mass seems to be feasible however the homogeneous model of the rock mass can only be applied to close stations within a few kilometers of the source the seismic records from distant stations were too complex to be modelled by a homogeneous rock mass records of six mine induced seismic events recorded at the kopanang gold mine were also inverted a vertical linear dipole along the pressure p axis was found for three of the events suggesting a pillar burst the mechanism of two events contains an isotropic implosion together with a nearly vertical dip slip and seems to indicate a combination of a cavity collapse with a down dip slip along a nearly vertical fault one event corresponds to a dipole along the tensional t axis however it is vertical thus its association with tensile faulting of the hangingwall is uncertain

assessment of quantitative aftershock productivity potential in mining induced seismicity strong mining induced earthquakes exhibit various aftershock patterns the aftershock productivity is governed by the geomechanical properties of rock in the seismogenic zone mining induced stress and coseismic stress changes related to the main shock s magnitude source geometry and focal mechanism in order to assess the quantitative aftershock productivity potential in the mining environment we apply a forecast model based on natural seismicity properties namely constant tectonic loading and the gutenberg richter frequency magnitude distribution although previous studies proved that mining induced seismicity does not obey the simple power law here we apply it as an approximation of seismicity distribution to resolve the number of aftershocks not considering their magnitudes the model used forecasts the aftershock productivity based on the background seismicity level estimated from an average seismic moment released per earthquake and static stress changes caused by a main shock thus it accounts only for aftershocks directly triggered by coseismic process in this study we use data from three different mines mponeng south africa rudna and bobrek poland representing different geology exploitation methods and aftershock patterns each studied case is treated with individual parameterization adjusted to the data specifics we propose the modification of the original model i e including the non uniformity of m0 resulting from spatial correlation of mining induced seismicity with exploitation the results show that even when simplified seismicity distribution parameters are applied the modified model predicts the number of aftershocks for each analyzed case well and accounts for variations between these values such results are thus another example showing that coseismic processes of mining induced seismicity reflect features of natural seismicity and that similar models can be applied to study the aftershock rate in both the natural and the mining environment

geological modeling for simulation studies reservoir heterogeneity is hierarchical in nature and different levels of reservoir heterogeneity need to be quantified by the reservoir geologist for numerical simulation studies at the largest scale field scale sand body continuity and interconnectedness are the most important parameters at the scale of a reservoir or a genetic sand body areal permeability trends presence and distribution of permeability baffles vertical profiles of permeability and presence of directional permeability within a sand body are the most critical parameters at a smaller scale the influence of cross bedding on displacement processes is shown to be significant and in fact should be assessed to obtain more meaningful results from larger scale simulation models the examples given show some of the effects of the different scales of heterogeneity on fluid flow patterns these examples indicate the degree of detail that must be considered at different scales if simulations are to give meaningful results

some observations on the influence of faults in mininginduced seismicity abstract the effect of faults on seismicity has been investigated for mining induced seismicity associated with coal extraction in the north staffordshire coalfield u k the studies show that seismic events occur if the mine workings cause the redistribution of strata pressure in such a way that sliding movements take place along major faults in particular movements occur when the active longwall face is driven in the footwall of the faults and parallel to the fault plane

the fluid dynamics of river dunes a review and some future research directions 1 dunes are present in nearly all fluvial channels and are vital in predicting flow resistance sediment transport and deposition within many rivers progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field laboratory and numerical investigations progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune additionally the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood with the feedback of dune three dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features this review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes five areas are then highlighted and discussed as a possible focus for future research 1 the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field 2 the influence of three dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress 3 flow field modification resulting from bed form superimposition and amalgamation 4 the scale and topology of dune related turbulence and its interactions with sediment transport and the flow surface and 5 the influence of suspended sediment on the dune flow field and dune morphology

frequency spectra and intermittency of the turbulent suspension process in a sand bed river previous research suggests that the turbulence driven suspension process in sand bed channels is dominated by intermittent energetic eddies with length scales of the order of channel depth because of the scarcity of data on the turbulent suspension process in alluvial channels the possible variability in suspension intermittency and turbulent frequency content due to contrasts in flow depth velocity or bedforms remains unclear however the present study analyses eddy correlation suspension signals from seven deployments in varied flow conditions around a sandy meander bend deployment depths at near bankfull flow stages varied from 2 to 5 5 m velocities at 0 75 1 m height from 0 6 to 0 9 m s 1 and local mean suspended sand concentrations ranged from 30 to 150 mg l 1 in the intermittence and spectral content of sand suspension between the various deployments are analysed and results are compared with previously published findings study data suggest that the dominant eddy sizes involved in sediment mixing across the sensor level are consistently of the order of 1 5 times flow depth and lie within the energy bearing turbulent range when sand suspension is analysed in the time domain in the various deployments energetic burst like suspension events occupying only 1 5 of the record duration account for 20 90 of the suspension work the degree of intermittence in the suspension process was observed to increase in deeper flows where mixing events contributing extreme vertical sediment fluxes appear to be relatively more frequent

false alarms and mine seismicity an example from the gentry mountain mining region utah as part of a large discrimination study in the western united states taylor et al 1989 one earthquake was consistently classified as an explosion the magnitude m 3 5 disturbance occurred on 14 may 1981 and was conspicuous in its lack of love waves relative lack of high frequency energy low lg pg ratio and high moment tensor additionally a moment tensor solution by patton and zandt 1991 indicated that the event had a large implosional component the event occurred in the gentry mountain coal mining region in the eastern wasatch plateau utah previous microearthquake studies in the region have demonstrated the existence of numerous small implosional events associated with the mining activities the event is more comparable in appearance at the broadband station at kanab utah knb to the atrisco collapse at the nevada test site nts than to another double couple event near the mining region using a simple source representation we modeled the event as a tabular excavation collapse that occurred as a result of normal mining activities this study raises the importance of having a good catalog of seismic data and information about mining activities from potential proliferant nations this information will be critical in resolving potential false alarms that may be generated from natural mine seismicity

in situ monitoring of rock fracturing using shear wave splitting analysis an example from a mining setting summary changing stress conditions are well known to cause rupturing of rock this is well constrained on a small scale from laboratory experiments and inferred on a much larger scale from tectonic earthquakes here we present a study of rock fracturing induced by changes in stress state during block caving operations in an australian mine this intermediate scale study provides further evidence of the scalability of processes involved in rock fracturing and thus helps to link laboratory and seismological observations we analyse the temporal evolution of rock fracturing during a production cycle using the analysis of fracture induced anisotropy fracturingoftherockmassismonitoredusingevidenceofseismicanisotropyfromestimates of shear wave splitting and their subsequent inversion for fracture parameters the data set consists of more than 40 000 three component seismograms recorded by an array of sensors which provides excellent ray coverage we applied a novel automatic quality assessment technique to handle this large data set and find that anisotropy and thus fracturing correlates strongly with the excavation process we then perform a grid search over a series of synthetic models based on rock physics to invert the splitting parameters for fracture orientation and density finally by applying a sliding window on our results we are able to identify production related fracture evolution during production the fracture density increases with horizontal fracture density being stronger than the vertical fracture density this can be explained by the removal of the supporting rock during caving during short intervals of reduced production the horizontal fracture density decreases whereas vertical fracture density increases we relate this to change in stress regime with reducing overburden mass during cavity collapse this scenario is similar to a collapsing caldera or the inverse of an inflating magma chamber

human induced seismicity and large scale hydrocarbon production in the usa and canada we compare current and historic seismicity rates in six states in the usa and three provinces in canada to past and present hydrocarbon production all states provinces are major hydrocarbon producers our analyses span three to five decades depending on data availability total hydrocarbon production has significantly increased in the past few years in these regions increased production in most areas is due to large scale hydraulic fracturing and thus underground fluid injection furthermore increased hydrocarbon production generally leads to increased water production which must be treated recycled or disposed of underground increased fluid injection enhances the likelihood of fault reactivation which may affect current seismicity rates we find that increased seismicity in oklahoma likely due to salt water disposal has an 85 correlation with oil production yet the other areas do not display state province wide correlations between increased seismicity and production despite 8 16 fold increases in production in some states however in various cases seismicity has locally increased multiple factors play an important role in determining the likelihood of anthropogenic activities influencing earthquake rates including i the near surface tectonic background rate ii the existence of critically stressed and favorably oriented faults which must be hydraulically connected to injection wells iii the orientation and magnitudes of the in situ stress field combined with iv the injection volumes and implemented depletion strategies a comparison with the seismic hazard maps for the usa and canada shows that induced seismicity is less likely in areas with a lower hazard the opposite however is not necessarily true

microearthquake mechanism from wave amplitudes recorded by a close to surface seismic array at ocnele mari romania the resolution of event mechanism is investigated in terms of the unconstrained moment tensor source model and the sheartensile crack source model representing a slip along the fault with an off plane component data is simulated as recorded by the actual seismic array installed at ocnele mari romania where sensors are placed in shallow boreholes noise is included as superimposed on synthetic data and the analysis explores how the results are influenced i by data recorded by the complete seismic array compared to that provided by the sub array of surface sensors ii by using threeor one component sensors and iii by inverting pand s wave amplitudes vs p wave amplitudes only the orientation of the pure shear fracture component is resolved almost always well on the other hand the noise increase distorts the non double couple components non dc of the moment tensor unless a high quality dataset is available the shear tensile crack source model yields considerably less spurious non shear fracture components incorporating recordings at deeper sensors in addition to those obtained from the surface ones allows for the processing of noisier data performance of the network equipped with threecomponent sensors is only slightly better than that with uniaxial sensors inverting both pand swave amplitudes compared to the inversion of p wave amplitudes only markedly improves the resolution of the orientation of the source mechanism comparison of the inversion results for the two alternative source models permits the assessment of the reliability of non shear components retrieved as example the approach is investigated on three microseismic events occurred at ocnele mari where both large and small non dc components were found the analysis confirms a tensile fracturing for two of these events and a shear slip for the third

variations in sediment texture on the northern monterey bay national marine sanctuary continental shelf abstract the storm protected continental shelf of monterey bay part of the monterey bay national marine sanctuary north central california is subject to abundant episodic sediment input from fluvial sources north of monterey bay conditions of reduced sediment supply combined with the exposed nature of the shelf provide an effective laboratory for studying the contrasting effects of storm versus fluvial dominated conditions on modern sedimentation textural analyses performed on surface sediment samples collected from more than 380 box cores and multicores document the existence of a clearly defined mud belt occupying the mid shelf throughout the region inshore sands combined with these mid shelf muds represent deposits from modern sedimentation processes in monterey bay where episodic fluvial input from winter storms dominates sedimentation the mid shelf mud belt extends across the shelf to the shelf break north of monterey bay where sediment loads are reduced and both oceanographic and storm processes dominate the mid shelf mud belt is bordered by relict sediments occupying the outer shelf in the study area mass accumulation rates established by radiochemical studies support the contention that storm induced along shelf processes result in northward transport of sediment within the mud belt the continuity of transport however is interrupted by topographic highs which are barriers or inhibitors to sediment transport created by wrench style tectonics associated with the san andreas fault system

interplay of stream subsurface exchange clay particle deposition and streambed evolution 1 hyporheic exchange mixing of stream water with pore water beneath the stream is responsible for the transport of many ecologically relevant substances across the stream subsurface interface this process is dependent on both the streamflow conditions and sedimentary properties but the complex nature of fluvial systems has presented a barrier to the development of mechanistic understanding of the dynamics of stream subsurface interactions this work presents the results of a controlled study to examine in detail the relationship between stream subsurface exchange fluxes delivery of suspended sediments to the hyporheic region fine particle accumulation in the streambed and alteration of sedimentary properties laboratory flume experiments were used to observe kaolinite clay deposition in a sand bed and the resulting alteration of hyporheic exchange fluxes solute and suspended sediment exchange with clean sand beds is predicted well by a fundamental model for bed form driven advective pumping exchange however substantial accumulation of clay in the bed causes an alteration of the pore water flow environment which reduces both water flux across the stream subsurface interface and subsequent particle deposition measurement of bulk solute exchange and direct observation of clay accumulation in the bed both indicate that transported fine particles are preferentially removed near the stream subsurface interface clogging of inflow regions produces heterogeneous subsurface clay deposits even when the bed is initially homogeneous this behavior is also predicted by the fundamental colloid pumping model these results contradict the accepted view that suspended sediments will generally deposit in the deepest regions of the bed and thus clog the bed from the bottom upward our results indicate that clogging of the streambed surface will often isolate deeper regions of the bed from the streamflow so that even relatively low amounts of suspended sediments can substantially degrade streambed habitat

a field study of turbulence and sediment dynamics over subaqueous dunes with flow separation this study examines flow turbulence and sand suspension over large dunes in canoe pass a distributary channel of the fraser river delta canada dune morphology is characterized by a symmetrical shape and steep leeside slopes over 30 velocity was measured with an electromagnetic current meter and suspended sand concentration with four optical backscatter obs probes the general patterns of time averaged velocity and sand suspension are consistent with previous studies including an increase in mean velocity and decrease in turbulence intensity and sand concentration with height above the bed reversed flow with high turbulence intensity and high sand concentrations in the leeside flow separation zone and an increase in near bed velocity and sand concentration along the stoss side of the dune frequency spectra of near bed velocity and obs records from leeside separation zones are composed of two distinct frequencies providing field confirmation of scale relations based on flume experiments the low frequency spectral signal probably results from wake flapping and the high frequency signal from vortex shedding the wake flapping frequency predominates outside the separation zone and is linked to turbulent structures that suspend sand predictions from a depth scale strouhal law show good agreement with measured wake flapping frequencies cross correlations of obs records reveal that turbulent sand suspension structures advect downstream at 23 25 above the horizontal these advection angles are similar to coherent flow structures measured in flumes and to sand suspension structures visualized over large dunes in the field

a comparison of characteristic parameters of mining related and tectonic seismic aftershock sequences abstract the temporal decay pattern of seismicity following rock bursts and large magnitude events is studied for aftershock sequences in several mines in ontario canada the decay phenomenon is described by the so called modified omori s law the dependency of the parameters k c and p with the magnitude of large mine seismic events is analyzed a total of eleven mining related seismic sequences with mainshock magnitudes ranging from 0 5 to 4 0 mn nuttli magnitude scale and from four different mine environments are examined results including the calculation of the gutenberg richter s and reasenberg jones parameters b and a are compared with previous research in tectonic seismicity using available data from new zealand italy and u s a further parameters were derived and applied in a correlation study of mining related and tectonic events the study revealed a good correlation between the productivity parameter a and b values particularly the b values show significant different number ranges for mining related and tectonic data which was applied to derive a direct numerical relationship between mining related and tectonic parameters and the aftershock number estimation finally numerical values for the b values in mining related seismic activity were obtained

rock mechanical analysis of a m1 4 0 seismic event induced by mining in the saar district germany summary on 2008 february 23 a 4 0 magnitude seismic event occurred in close proximity to a deep underground longwall coal mine in the german saar mining district preceding this event was a series of smaller seismic events which can be traced back to geological structures a seismic network was installed to observe and analyse the seismic events underground core drilling was performed to obtain rock samples for rock mechanical testing possible causes for the events failure of rock mass or slip on unknown faults are evaluated by numerical methods failure of rock mass is excluded as a cause since the stresses are well below the strength of the rock mass seismic events are of similar fault plane strike and are organized in several clusters associated with local and regional tectonic elements it was found from backcalculation that fault planes with friction angles as low as 8 must have been present the role of pore pressure on the fault stability is discussed and found to play no role in generating the seismic events finally the question of mining in a rock mass obviously close to failure is addressed and it was concluded that any mining activity would lead to a significant seismic response

bed form development based upon the results of a series of 47 bed development experiments the evolution of bed features subsequent to their initial generation from flat bed conditions is examined for each such experiment bed profiles were measured at frequent time intervals as sand wave configurations developed under the action of open channel water flow the two sediments used for these experiments were of geometric mean size 0 20 mm and 0 82 mm respectively in line with the bed form unification model of bed development postulated by saudkivi and witte in 1990 the principle of bed form propagation speed decreasing with increasing bed form height and the mechanisms of bed form coalescence and bed form throughpassing are all found to be central to bed evolution processes a quantitative relation between bed form speed and bed form height is presented bed development predictions based upon bed form unification models can be seen to clearly parallel the present experimental results stability analyses based upon potential

source analysis of post blasting events recorded in deep copper mine poland seismic and rock burst hazard is a very important factor that has to be considered in seismically active mining areas several different methods are used to decrease seismic activity in mines among others an active prevention method known as destress blasting is considered the most effective technique the aim of this work is to find possible influences of such active prevention on observed seismic activity recorded in the established waiting time after blasts using technological knowledge and seismic data recorded by an underground seismic network we estimated several parameters that characterize sources provoked by blasting works and compared them with the parameters obtained for spontaneous non provoked mining tremors according to our studies the source mechanisms of post blasting seismicity are characterized by the similar non dc part of the full moment tensor whereas the source mechanisms of spontaneous events are not characterized by any specific features on the other hand non provoked seismicity presents lowest values of apparent stress also es to ep ratio suggest some differences between events occurred immediately after blasting up to 30 s and the rest dataset we believe that these parameters could be considered valuable tools supporting established safety time limitations after active prevention

bedform migration and bed load transport in some rivers and tidal environments reliable field data obtained by directly measuring bed load transport of fine to coarse grained bed material are extremely scarce mainly because of the difficulty of sampling accurately therefore the verification of bed load transport formulae is largely based on flume experiments which refer to unrealistic shallow water conditions in this study some bed load transport formulae were tested against data from natural environments as an alternative to ascertaining the bed load transport rate by sampling the bed load the transport rate was deduced from data on bedform height and bedform celerity for this purpose 43 sets of data from rivers representing a wide range of bed material bedform dimensions and hydraulic conditions were collected as were some sets of data from tidal settings two formulae were used for the prediction of the bed load transport the formula of van rijn 1981 and the kalinske 1947 formula as approximated by elzerman frijlink 1951 and in the present study slightly modified for application to tidal waters both the bed load function of van rijn and the modified formula of kalinske frijlink require data which are easily obtained and that can be measured accurately at those stages of the flow when bed load transport was high the van rijn function tended to overestimate that transport for flow stages when bed load transport was low the opposite was true the modified kalinske frijlink function gave consistently good results 86 of the transport rates predicted using the river data were within 0 5 2 0 times the values actually measured

mining induced stress transfer and its relation to a text m _w 1 9 seismic event in an ultra deep south african gold mine on 27 december 2007 a text m w 1 9 seismic event occurred within a dyke in the deep level mponeng gold mine south africa from the seismological network of the mine and the one from the japanese german underground acoustic emission research in south africa jaguars group the hypocentral depth 3 509 m focal mechanism and aftershock location were estimated since no mining activity took place in the days before the event dynamic triggering due to blasting can be ruled out as the cause to investigate the hypothesis that stress transfer due to excavation of the gold reef induced the event we set up a small scale 450 times 300 times 310 text m 3 high resolution three dimensional 3d geomechanical numerical model the model consisted of the four different rock units present in the mine quartzite footwall hard lava hanging wall conglomerate gold reef and diorite dykes the numerical solution was computed using a finite element method with a discretised mesh of approximately 10 6 elements the initial stress state of the model is in agreement with in situ data from a neighbouring mine and the step wise excavation was simulated by mass removal from the gold reef the resulting 3d stress tensor and its changes due to mining were analysed based on the coulomb failure stress changes on the fault plane of the event the results show that the seismic event was induced regardless of how the coulomb failure stress changes were calculated and of the uncertainties in the fault plane solution we also used the model to assess the seismic hazard due to the excavation towards the dyke the resulting curve of stress changes shows a significant increase in the last sim 50 text m in front of the dyke indicating that small changes in the mining progress towards the dyke have a substantial impact on the stress transfer

spectral analysis of turbulent flow and suspended sediment transport over fixed dunes laboratory measurements of turbulent fluctuations in velocity and suspended sediment concentration were obtained synchronously over fixed two dimensional dunes in a sediment starved flow contour maps of turbulent flow parameters demonstrate that the flow separation cell and a perturbed shear layer are the main sources of turbulence production and that the distribution of suspended sediment is controlled by spatially dependent macro turbulent flow structures spectral analysis reveals that peak spectral energies generally occur at 1 2 hz for the stream wise velocity component and 2 4 hz for the cross stream and vertical velocity components spectra show larger and better defined energy peaks near the shear layer peak spectral energies for suspended sediment concentration occur near 1 hz throughout the flow squared coherency values for cospectral analysis of velocity and sediment concentration are insignificant integral timescales for velocity range from 0 20 s for the streamwise component to 0 06 s for the cross stream and vertical components integral length scales for velocity range from 0 065 to 0 135 m for the streamwise component which is comparable to flow depth and from 0 020 to 0 030 m for the crossstream and vertical components which is comparable to dune height for suspended sediment concentration integral timescales and length scales are similar to the streamwise velocity component

temporal and spatial variations in sand budgets with application to southern monterey bay california abstract often in calculating a sediment budget there is an unknown contribution which is ascribed to the residual of the balance and the budget cannot be fulfilled the temporal and spatial variations and sediment size within a littoral cell provide additional information to define sediment budgets the approach here is to consider only medium to coarse sand grain size 0 25 mm over a long time period during significant changes of natural and anthropogenic inputs and losses that allow calculating several budgets to isolate the unknown inputs and outputs to close the system considering only medium to coarse sand eliminates including the cross shore transport of fine sand by waves which is poorly quantified to demonstrate these concepts shoreline recession rates measured over a 101 year time period are used to calculate sediment budgets for southern monterey bay california littoral cells the coarse sandy shoreline is backed by extensive bluffs and dunes that reach 44 m in elevation intensive sand mining of coarse sand derived directly from the beach and surfzone started in 1927 and continues today a contribution of about 100 k m 3 year of medium to coarse sand from the salinas river is calculated from measured shoreline accretion for the period 1910 1945 starting when the river first flowed into the littoral cell prior to damming of the river and significant losses owing to sand mining sediment budgets are calculated for 1940 1989 and 1989 2011 to spatially identify the loss of about 200 k m 3 year attributed to different mining operations that captured the littoral transport the primary contributions of medium to coarse sand to the littoral system is approximately 180 k m 3 year from the eroding dunes and beaches only a quarter of the dune sand is found to be compatible with the coarser beach sand with the finer fraction carried offshore a conclusion is that sand mining is the cause of the observed high recession rates

on the transition between 2d and 3d dunes sediment transport in sand bedded alluvial channels is strongly conditioned by bedforms the planimetric morphology of which can be either two or threedimensional experiments were undertaken to examine the processes that transform the bed configuration from two dimensional 2d dunes to threedimensional 3d dunes a narrowly graded 500 lm size sand was subjected to a 0ae15 m deep non varying mean flow ranging from 0ae30 to 0ae55 m sec 1 in a 1 m wide flume changes in the planimetric configuration of the bed were monitored using a high resolution video camera that produced a series of 10 sec time lapsed digital images image analysis was used to define a critical value of the non dimensional span sinuosity of the bedform crestlines that divides 2d forms from 3d forms significant variation in the non dimensional span is observed that cannot be linked to properties of the flow or bedforms and thus appears random images also reveal that once 2d bedforms are established minor transient excesses or deficiencies of sand are passed from one bedform to another the bedform field appears capable of absorbing a small number of such defects but as the number grows with time the resulting morphological perturbations produce a transition in bed state to 3d forms that continue to evolve but are pattern stable the 3d pattern is maintained by the constant rearrangement of crestlines through lobe extension and starving downstream bedforms of sediment which leads to bifurcation the experiments demonstrate that 2d bedforms are not stable in this calibre sand and call into question the reliability of bedform phase diagrams that use crestline shape as a discriminator

turbulent flow over three dimensional dunes 2 fluid and bed stresses 1 dunes formed in response to fluid flow exert a total boundary stress on the fluid that is made up of form drag and skin friction the latter of which is generally considered important for predicting sediment transport and dune evolution previous research has used various methods to estimate the total stress and its subcomponents with recent work suggesting the application of a spatial average to the equations of motion a complete three dimensional 3 d form of this analysis is derived and applied to recent measurements of turbulent open channel flow over 3 d dunes spatial averages of reynolds shear stresses over 3 d dunes cannot be used to predict total boundary shear stress however estimations of total boundary shear stress from the spatially averaged equations of motion agree with not only the sum of form drag and skin friction but also the direct measurements of average free surface slope form induced stresses from secondary circulations augment the relatively low reynolds shear stresses over the 3 d dunes these low turbulence levels have ramifications for sediment transport predictions in that use of the total boundary shear stress in prediction of sediment transport over 3 d dunes must account for these low turbulence levels so as not to overpredict transport rates

ground motions induced by mining seismic events with different focal mechanisms abstract it is essential to quantify the ground motions induced by seismic events with different focal mechanisms in underground mine to quantitatively calculate the induced ground motions we expressed the motions as the convolution of the seismic source and the wave propagation path using seismological method firstly we investigated the theoretical ground motion patterns using four idealized focal mechanisms results show that the pure compressional failure source and the pure tensional failure source induced the same ground motion patterns the vibrations they induced attenuate extremely fast the pure shear failure source shows closely azimuth related pattern with four quadrants around the source the pure explosive failure source induces vibrations attenuating toward all directions away from the source but the vibrations are not attenuated gradually with the increasing distance then we investigated the ground motions under complicated focal mechanisms using recorded fault slip events cavity collapse events and tensional failure events the fault slip events show a four quadrants ground motion distribution in the horizontal plane and a two quadrants distribution in the vertical plan but the cavity collapse events show a two quadrants distribution in the horizontal plane and a four quadrants distribution in the vertical plane it is concluded that the induced ground motion at a certain location is controlled by the dual effects of the azimuth and the source focal mechanism as well as the distance and the source magnitude

morphology sedimentology and palaeohydraulic significance of large gravel dunes altai mountains siberia coarse gravel bedforms which resulted from pleistocene glacial outburst floods are identified as subaqueous dunes comparison of the morphology of these fossil structures with modern dunes shows that the form of two dimensional 2 d transverse dunes and 3 d cuspate and lunate dunes developed in coarse gravels is comparable with sand dune morphology within lesser scale geophysical flows the similarity of the steepest gravel dunes with equilibrium dunes in sand indicates that grain size is not a major factor in constraining primary duneform internal structure indicates that flow over 2 d dunes was relatively uniform but over 3 d bedforms flow was locally variable flow separation and complex streaming of flow occurred over the steepest 3 d dunes cross beds are thin and few approach the angle of repose consequently most dunes did not migrate primarily by avalanching but by stoss entrained gravel transported over the crests rolling down and depositing on the lee slopes the lee formed when flood power was waning some dunes were siightly planed down during falling stage because lee side cross beds tend to be steeper than the angle of the preserved lee slope however silt rich caps indicate that any height reduction was contemporary with the final deposition of foresets post flood modification has been negligible although the modern topography is subdued by loess deposits within the dune troughs lee side sediments are often finer than the stoss slope sediments which indicates

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany ii hydrodynamics and sediment transport the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine during daylong surveys suspended sediment concentration bedload transport rate water depth flow velocity turbulence intensity near bed shear stress and water temperature were recorded over individual isolated dunes this paper considers the hydrodynamic environment and sediment transport over the dunes a companion paper details the sedimentology and morphology of the dunes flow over the flat gravel lag upstream of large dunes is more uniform than that over dunes and gravels are rarely entrained by in bank discharges unsteady and non logarithmic velocity profiles are common within the boundary layer above the stoss side of large dunes and the near bed flow demonstrates evidence of large scale coherent low frequency flow structures these may reflect stacked sequences of separated boundary layers generated by secondary dunes however the low amplitude morphology of large dunes does not affect the statistical properties of turbulence production over the stoss sides bed roughness and near bed shear stress commonly increase steadily over the stoss of dunes but may decrease near the crest especially where a crestal platform exists that is devoid of secondary bedforms bed roughness scales with the physical size of bed roughness elements however variability in roughness lengths is large owing to the composite nature of bed roughness bedload transport over stoss slopes is spatially variable but often shows an increase with increasing bed shear stress over the stoss well formed wakes only develop downstream of lee slopes which are close to the angle of repose otherwise separation is weak and suspension and settling of fine sediments is of little consequence to dune evolution wake flow is characterized by turbulence production one order of magnitude greater than over the stoss side which may be related to vortex shedding from the dune however wake current speeds are extremely low and variable in direction reverse flow is not sustained and no retrogressive bedforms occur in the lee of large dunes near bed shear stress and bed roughness are usually low within the wake reflecting low current speeds weak wake flow reattachment occurs at a variable distance downstream up to several times the duneform height a two dimensional numerical model for flow over dune topography calibrated using average parameter values provided a reasonable description of the flow upstream and over the backs of large dunes as far as the crestal region wake flow could not be modelled however the temporal and spatial complexity of natural three dimensional flow over the dunes resulted in variance in parameter estimates this variance precluded modelling of flow and bedload transport consequently it was not possible to model dune evolution in a deterministic sense

aftershock sequences of the 1982 miramichi new brunswick earthquakes the mb 5 7 miramichi new brunswick earthquake of 9 january 1982 was located by comparison to the aftershock distribution in central new brunswick canada at 47 00 n 66 60 w with a focal depth of 7 km and an uncertainty of 3 km on each of the spatial coordinates the main shock was followed by a long and complex aftershock sequence with four events m 4 5 and more than 800 events m 1 0 until 30 june 1982 the aftershocks were studied by three temporary field networks set up in the epicentral areas from 10 to 20 january 2 to 7 april and 17 to 23 june 1982 and by the permanent canadian seismograph networks the aftershock activity was concentrated in a volume approximately 6 km ns 6 km ew 8 km deep and arranged in a north trending conjugate v pattern the miramichi earthquakes were predominatly thrust earthquakes occurring on north trending mid to high angle faults in the upper 8 km of the crust in the presence of an east west compressive horizontal regional stress field detailed field surveys have not yet been able to associate the earthquakes with any known preexisting faults the main shock had a moment of 2 2 0 7 1024 dyne cm and a stress drop of 35 to 70 bars the rupture started at 7 km depth on a plane striking 195 dipping 50 down to the west and propagated up to the east with a rake angle of 120 aftershocks deeper than 3 5 km had composite mechanisms very similar to the main shock s but shallower events took place on more steeply dipping planes up to 78 dip the rupture planes of the main shock and its principal aftershocks may have been similarly curved the magnitude frequency relationship b 0 8 of the aftershocks was comparable to the regional one the aftershock activity decayed as t 0 8 and had the highest rate of activity following the principal aftershock on 11 january that aftershock mb 5 4 appears to have ruptured the east dipping plane conjugate to the main shock s plane two other principal aftershocks mb 5 1 on 9 january and mb 5 0 on 31 march were associated with the main shock rupture plane while the fourth large event mb 4 7 on 16 june occurred 30 km west of the other activity and was seemingly unrelated however all the earthquakes were apparently associated with the same granitic terrain the miramichi earthquakes did not produce any significant surface faulting one small 25 mm surface displacement was found but it was identified as a secondary stress induced movement along a preexisting joint

location of microseismic swarms induced by salt solution mining ground failures caving processes and collapses of large natural or man made underground cavities can produce significant socio economic damages and represent a serious risk envisaged by the mine managements and municipalities in order to improve our understanding of the mechanisms governing such a geohazard and to test the potential of geophysical methods to prevent them the development and collapse of a salt solution mining cavity was monitored in the lorraine basin in northeastern france during the experiment a huge microseismic data set similar to 50 000 event files was recorded by a local microseismic network 80 per cent of the data comprised unusual swarming sequences with complex clusters of superimposed microseismic events which could not be processed through standard automatic detection and location routines here we present two probabilistic methods which provide a powerful tool to assess the spatio temporal characteristics of these swarming sequences in an automatic manner both methods take advantage of strong attenuation effects and significantly polarized p wave energies at higher frequencies 100 hz the first location approach uses simple signal amplitude estimates for different frequency bands and an attenuation model to constrain the hypocentre locations the second approach was designed to identify significantly polarized p wave energies and the associated polarization angles which provide very valuable information on the hypocentre location both methods are applied to a microseismic data set recorded during an important step of the development of the cavity that is before its collapse from our results systematic spatio temporal epicentre migration trends are observed in the order of seconds to minutes and several tens of meters which are partially associated with cyclic behaviours in addition from spatio temporal distribution of epicentre clusters we observed similar epicentre migration in the order of hours and days all together we suggest that the recorded microseismicity mainly represents detachment and block breakage processes acting at the cavity s roof indicating a zone of critical state of stress and where partial fractures cause chain reaction failures as a result of stress redistribution processes