numerical modelling of strata movement at footwall induced by underground mining abstract during metal mining the deformation and failure of rock mass are very important factors that dominate rock movement and zoning numerical modelling provides a feasible way to study the deformation and failure of rock mass in this study a numerical method of udec was adopted to study strata movement mechanism influenced by nww trending joints at the footwall at chengchao iron mine and the mohr coulomb model and the coulomb slip model with residual strength were adopted as the constitutive models of rock masses and joints respectively the whole strata movement process was simulated and the strata movement mechanism at footwall and zoning phenomenon was clarified in the chimney caving development stage gravity is the driving force and surface deformations are mainly subsidence deformation of the surface above the ore body in the post chimney deformation stage horizontal tectonic stress is the driving force and surface deformation and subsidence are dominated by horizontal deformation of the hanging wall and footwall in the mining area after the level 395 0 m is mined out the deformation characteristics of deep surrounding rock were revealed by means of numerical modelling the maximum failure depth of the cantilever beam and the spatial distribution of deep surrounding rock zones can be determined at last the influencing boundary of surface deformation expands rapidly in a linear way with the excavation step and the expanding velocity of the horizontal deformation is greater than that of the subsidence in the post chimney deformation stage

u pb and sm nd isotopic constraints on the evolution of the paleoproterozoic perapohja belt northern finland ten localities representing metasedimentary and igneous rocks from the northern part of the paleoproterozoic perapohja belt fennoscandian shield were sampled for zircon u pb dating by la mc icp ms and sm nd analysis by tims the results revealed two phases of granitic magmatism that took place at 1 99 ga and 1 79 1 77 ga the former age 1989 6 ma was given by the kierovaara granite pluton representing the first example of felsic plutonism of this age in northern finland though a type felsic volcanic rocks of the same age have previously been recognized the strongly negative initial nd values obtained for granitoids ranging from 3 9 to 11 4 are compatible with the previous sm nd data indicating the presence of archean basement in northern finland at the time of granite emplacement a garnet whole rock sm nd age of 1752 14 ma was measured for a mica gneiss constraining the time of metamorphic cooling down to the closure temperature of garnet detrital zircon grains from quartzite samples belonging to the jatulian palokivalo formation and a stratigraphically unassigned lithodemic unit the mellajoki suite yielded solely archean zircon populations in contrast our sample from the martimo formation representing kalevian sedimentation revealed a 66 paleoproterozoic detrital zircon component with the youngest zircon grains showing an age of ca 1 91 ga the new age data allow us to constrain the depositional time of this sedimentary unit between ca 1 91 and 1 88 ga the latter being the time of the synorogenic plutonism our geochronological data coupled with recent data from other karelian belts suggest that the depositional time period for rocks assigned to the kaleva spans ca 150 ma and the simple division of these rocks into two non coeval units the lower and upper kaleva has become problematic

delamination of eclogitized lower crust control on the crust mantle boundary in the central fennoscandian shield abstract the crustal structure of the central part of the fennoscandian shield is dominated by a high velocity lower crust hvlc vp 7 3 7 5 km s at the depth of 40 63 km in an area of ca 400 km 600 km formed in the palaeoproterozoic svecofennian orogen at 1 91 1 87 ga in the area of the hvlc the moho is deeper than 50 km and attains depths of up to 63 km in eastern finland at the archaean proterozoic boundary zone we suggest that the present moho dates back to late svecofennian time and was determined by delamination of high density eclogitized lower crust after tectonic collisional thickening of crust densities deduced from seismic and gravity data suggest a very small or completely lacking density contrast between lower crust and uppermost mantle new geological evidence from kimberlite hosted garnet xenocrysts supports the presence of a garnet population with compositions in agreement with crustal eclogitic garnets in addition small clinopyroxene garnet mineral aggregates microxenoliths show omphacitic clinopyroxene compositions therefore the presence of eclogites in the high velocity lower crust is implied although the eclogite proportion as estimated from seismic velocity data is only a few percent in the present hvlc with results on near incidence and wide angle seismic studies and geological and geochemical data on heat producing elements we modeled the svecofennian collision and the thermal evolution of the crust to provide temperature constraints for the delamination model the constructed thermal model simulates the genesis of svecofennian synkinematic at 1 89 1 88 ga and postkinematic 1 88 1 87 ga granitoids as well as the general metamorphic grade of the surface rocks and lower crustal xenoliths moreover the narrow distribution of the ages of the svecofennian mafic ultramafic magmatism ca 1 89 1 87 ga dispersed around the hvlc area is explained by the homogeneous warming of the lithosphere the conditions of lower crustal delamination were estimated with a rayleigh taylor convective instability model constrained with lower crustal and upper mantle rheological data delamination of a lower crustal eclogite layer 5 30 km thick takes place in about 7 50 ma if the rock dynamic viscosity is 1 1021 pa s it requires temperatures of 1000 c in the lower crust and upper mantle in the svecofennian crust such temperatures were attained at about 1860 1850 ma i e after the orogenic peak we conclude that the moho of the hvlc area was controlled by delamination of a ca 5 10 km thick layer of high density lowermost crust into the mantle such a density controlled process may have controlled the moho depth also in other proterozoic shield areas

three zone characterisation of coupled strata and gas behaviour in multi seam mining abstract we propose here a three zone conceptual model in overlying strata of a longwall panel that accounts for the coupled behaviour of strata deformation and gas flow the model comprises a fractured gas interflow zone a de stressed gas desorption zone and a confined gas adsorption zone the fractured gas interflow zone represents the area where mining induced cross strata fractures and bedding separations are well developed with high permeability in both the vertical and horizontal directions coal seam gas can easily be released from this lower zone to flow down into the mine workings the de stressed gas desorption zone which lies above the fractured gas interflow zone is another significant gas producing zone in which strata are highly de stressed however mining induced fractures in this zone are mainly created in the form of bedding separations which only increase horizontal permeability and thus the gas cannot easily flow vertically down to the mine workings in the upper confined gas adsorption zone strata depressurisation is limited the major proportion of coal seam gas in this zone remains adsorbed and cannot be effectively captured while both lower zones are the targets of gas drainage the fractured gas interflow zone is the main source of ventilation gas emission and the prime area of gas control we have developed an approach to determine the height of these three zones based on the hypothesis of key stratum in strata movement and verified the approach using gas drainage experience at a chinese coal mine the applications of the three zone concept in selecting appropriate gas drainage methods for varied mining conditions assessment of methane recovery efficiency and gas drainage optimisation and maximisation in a mining district of china are also discussed

three dimensional time lapse velocity tomography of an underground longwall panel three dimensional velocity tomograms were generated to image the stress redistribution around an underground coal longwall panel to produce a better understanding of the mechanisms that lead to ground failure especially rockbursts mining induced microseismic events provided passive sources for the three dimensional velocity tomography surface mounted geophones monitored microseismic activity for 18 days eighteen tomograms were generated and high velocity regions correlated with high abutment stresses predicted by numerical modeling additionally the high velocity regions were observed to redistribute as the longwall face retreated indicating that velocity tomography may be an appropriate technology for monitoring stress redistribution in underground mines

thermal properties of granulite facies rocks in the precambrian basement of finland and estonia abstract we present results of heat production thermal conductivity and p wave velocity measurements of 252 rock samples from five granulite facies areas in finland and estonia these compositionally mainly intermediate archaean and palaeoproterozoic metamorphic rocks have relatively high heat production values mean values averaged by areas range from 0 57 to 2 24 w m 3 the lowest values are in the varpaisjarvi area which is the oldest and most mafic and where the highest metamorphic pressure occurred 8 11 kbar whereas the highest heat production is found in the turku granulite belt where the metamorphic pressure was 4 6 kbar the heat production decreases with the increase of the metamorphic pressure however a general numerical relationship cannot be presented because of considerable variations in heat production data there is no significant difference in the metamorphic temperatures of the studied granulites and therefore no dependence on temperature is found further our data suggest no relationship between heat production and p wave velocity the mean thermal conductivity of granulites varies from 3 0 to 3 5 w m 1 k 1 slightly elevated thermal conductivity values in the varpaisjarvi and lapland granulite areas can be attributed to higher sillimanite and quartz contents respectively

microseismic signals of double layer hard and thick igneous strata separation and fracturing abstract in order to analyze the microseismic ms effects of hard and thick igneous strata separation and fracturing and the corresponding evaluation index of fracturing intensity the temporal spatial evolution of the ms sources generated by igneous strata fracturing in the 10416 working face of the yangliu coal mine ycm was dynamically recurred and the waveform and frequency spectrum distribution characteristics of primary and igneous strata fracturing were clearly investigated respectively in addition the relationship between the ms dominant frequency the energy ratio in low frequency band and the intensity of igneous strata fracturing was revealed and the energy ratio of ms event in low frequency band can be verified as an effective index for evaluating roof fracturing intensity the work may put forward a certain reference for early warning and evaluating hard and thick roof fracturing and the induced coal rock dynamic disasters based on in situ ms observation

numerical investigation of the effects of coal seam dip angle on coal wall stability abstract instability and failure mechanism of coal wall at coalface is one of the hot button and difficult issues in the study of coal mine ground control research to date has mainly focused on the macro characteristics of coal face failure whereas few efforts have been devoted to the micro aspects or to the mechanisms behind these failures the work described here takes coal face 8102 in the wolonghu mine china as an example and employs distinct element numerical software udec to investigate the distribution of abutment stress in front of the coal face at different mining dip angles from micro and macro perspectives and reveal the main failure form and location of coal rib the numerical results indicate the following six points 1 the distance between the location of the peak abutment stress and the coal face increases with greater mining dip angles 2 the rank by angle of abutment stress concentration factors is horizontal up dip down dip coal faces 3 tensile fractures dominate the failure of horizontal and up dip coal faces and the only difference between the two is the form of the failure 4 shear fractures are the dominant failure components of down dip coal faces 5 the coal face failure forms include integral rib spall and a combination of upper rib shear failure and roof caving 6 tensile fractures are mainly responsible for roof failures the difference in roof movement between up dip and down dip coal faces is reflected in the forms of failure of their coal faces and of their roofs moreover the effect of coalface depth mining height panel advance velocity and coal strength on the stability of coal rib is studied the conclusions obtained from numerical simulation are consistent with engineering result which verifies the reasonability of simulation analysis by udec finally we propose measures to avoid coal face failure in the wolonghu mine considering the numerical outcomes the monitored strata behavior and the recorded setting support resistance

characteristics of stratum movement induced by downward longwall mining activities in middle distance multi seam abstract with the development of mining depth multi seam mining activities is becoming more and more frequent correspondingly the study on stratum movement characteristics induced by multi seam mining activities is of great significance for preventing water inrush disaster and forecasting support pressure surface deformation gas drainage and other mining problems according to the interaction among the caved zone the fractured zone and the continuous deformed zone caused by the multi seam downward mining activities multi seam can be divided into three types i e the short distance middle distance and long distance multi seam this paper carries out a case study on the middle distance multi seam mining activities in a coal mine in china to investigate the characteristics of stratum movement caused by downward longwall coal mining activities in the multi seam by means of borehole water level observation digital borehole camera test microseismic monitoring surface crack observation of the surface cracks and distinct element modelling by analyzing the in site monitoring results and the numerical simulation results it can be found that the failure of the key stratum between the lower and upper seams resulting in the connection between the failed zone in floor induced by the upper seam and the fractured zone induced by the lower seam after the failure of the key stratum the mining activities of the lower seam has a great influence on the secondary stratum movement in the overburden these effects are mainly reflected in the rapid increase of horizontal displacement and vertical displacement which caused the caved and fractured zones extend upward in the overburden and then surface cracks increase significantly the above research results are of great significance for the prevention and control of disasters induced by downward longwall mining activities in middle distance multi seam

interpretation of gravity anomalies along the polar profile in the northern baltic shield abstract the polar profile in the northern baltic shield was analyzed by two and three dimensional quantitative gravity modelling interpretation of fourier amplitude spectra qualitative interpretation using bouguer anomalies and second vertical derivative and horizontal gradient maps and reference to petrophysical data densities of outcropping crustal units show several distinct modes ranging from 2600 to 2990 kg m3 in relation to the mean background density of 2690 kg m3 used in the gravity modelling the granitic crustal units 2600 kg m3 produce well defined gravity lows of up to 20 mgals and the granulites 2750 kg m3 and greenstones 2940 kg m3 cause the most pronounced gravity highs of 30 and 45 mgal the estimated thickness of the kittila greenstone belt is about 6 km in the cross section along the polar profile the base of the lapland granulite belt dips to the northeast and reaches a maximum thickness of about 16 km the thickness of the vainospaa granite body is approximately 6 km evidence of buried anomaly sources also exists our interpretation predicts units of increased density in the basement under the varanger peninsula sedimentary rocks the general pattern of a gravity high near the barents sea coast coupled with a gravity low seawards implies a thick layer of sedimentary rocks under the sea which may be compensated by crustal thinning according to the seismic refraction interpretation there is a depression in the moho under the southwestern edge of the lapland granulite belt explaining together with other features of the seismic model the regional background on which the gravity anomaly of the granulite belt is superposed according to the fourier analysis of gravity anomalies there are two dominant depth clusters of density discontinuities in the southwestern karelian province and middle parts lapland granulite belt of the polar profile the shallower discontinuity varies between 6 and 10 km and the deeper one rises from about 20 km in the southwest to about 10 km in the middle area in the northwestern part inari and sorvaranger terrains and varanger peninsula there are many separate depth values and clusters exist only at depths between 13 and 15 km

scully field marion county kansas abstract the scully field is a multipay new field discovery located in the southern end of salina basin marion county kansas since discovery in november of 1981 r j walker oil co inc has drilled and completed successfully 15 wells within the field productive depths are 3 300 ft 1 000 m and production capabilities of individual wells can exceed 300 bbl of oil day 24 hr gauges oil is trapped structurally within the viola and simpson units ordovician and trapped by a combination of erosional truncation and structure in the mississippian units the scully field was discovered using a combination of satellite imagery and subsurface control structural lineaments recognized from satellite imagery in conjunction with an understanding of the structural timing and framework of the salina basin enabled the definition of the structural unit which contains the scully field subsurface control prior to discovery although relatively sparse was sufficient in light of these structural elements to define the prospective area of the scully structure subsequent drilling has not altered significantly the potentially productive area the overall trapping mechanism at the scully field is anticlinal closure infield drilling has demonstrated however that significant stratigraphic variations do exist within the productive area the stratigraphic variations within the ordovician reservoirs are controlled strongly by paleostructure the simpson sands have been subdivided in five separate units which range from 4 to 12 ft 1 to 4 m in thickness three of these are of economic importance in the field in general the sands with the most economic potential are distributed within relative ordovician paleolows core analysis demonstrates that pay intervals have porosities of 14 to 18 and permeabilities of 200 to 500 md air whole core dean stark analysis the viola has four main lithologic divisions the uppermost of these is a relatively thin dolomite cap which ranges from 2 to 15 ft 1 to 5 m this upper dolomite is the primary viola pay zone core analysis indicates that this interval has porosities of 6 to 12 and permeabilities of 30 to 140 md air whole core dean stark analysis in general this dolomite is best developed on the ordovician paleohighs the mississippian section is eroded deeply over the scully structure and demonstrates about 70 ft 20 m of thinning the potential pay interval is chert which has 25 to 30 porosity based on log analysis the pay interval is absent over the portion of the field that is highest on present day structure at the ordovician level the trapping mechanism is a combination of erosional truncation and structural closure in addition to the structural information obtained from satellite imagery r j walker oil co inc evaluated the hydrocarbon potential of t18s r1e marion county kansas which contains the scully field using remote sensing technology developed by earth reference systems of long beach california the technology involves direct detection of hydrocarbons in place using satellite data nonlinear mathematics and the fundamental principles of molecular structure and electromagnetic wave propagation this analysis was made several months after the discovery well had been drilled in the scully field the conformance of these data within the structural and geologic confines of the scully field after 14 development wells drilled by r j walker oil co inc and two recent dry holes rilled by outside operators provides an interesting glimpse at technology that may revolutionize the way the oil and gas industry searches for new reserves end of article last page 1327

tectonic framework of powder river basin wyoming and montana interpreted from landsat imagery linear features in the powder river basin wyoming and montana were interpreted from landsat images and analyzed to define major lineaments lineaments identified include several that trend northwest and a prominent set that trends northeast these lineaments represent broad 5 10 km or 3 6 mi linear zones where smaller parallel and subparallel linear features are concentrated at the surface the smaller linear features are interpreted as possible expressions of joints fractures folds or lithologic boundaries produced by periodic readjustment along basement block boundaries the lineaments discussed in this report were visually interpreted from maps of linear features and contour maps showing concentrations of linear features lineaments were subsequently compared to mapped structures outcrop patterns geophysical data and isopach maps to assess their geologic significance correlations of these lineaments with mapped structures geophysical gradients or facies changes strongly support the interpretation that they represent the surface expression of boundaries of crustal blocks that have been periodically reactivated through time the northeast and northwest patterns provide evidence that a systematic rectilinear pattern of crustal blocks formed early in the earth s history and has largely controlled subsequent adjustments of the earth s crust these findings suggest the potential for depositional control of sedimentary units by structural adjustments between basement blocks and thus lead to the conclusion that lineaments may be used as guides in petroleum and mineral exploration if favorable source and host rocks are present

an experimental and numerical investigation on the deformation of overlying coal seams above double seam extraction for controlling coal mine methane emissions abstract this study investigates the deformation and the resultant pressure relief of highly gassy coal seams where a double seam mining operation takes place at lower depths at the wulan coal mine china in order to predict the depressurization effect in the overlying coal seams we simulate the extraction process by constructing a scaled model in the laboratory using similar rock materials analyses of experimental results concluded that due to the mining induced stress redistribution the pressure within target coal seams which were 109 m above the mined seams could be fully relieved to attain the statutory approval for gas drainage in addition to scaled model studies computational modeling studies were conducted using udec universal distinct element code which showed that the features of deformation resulting from the double seam extraction were different from that of in the case of single seam extraction the results of the numerical studies revealed that in addition to the panel margin on the air return side areas near the intake entry could also be considered as borehole drilling positions besides it was found that the gob of the extracted seams below the gassy one provided a buffering effect for the would mined protective coal seam and that the depressurization effect was largely weakened the laboratorial findings are instructive to the field practice of methane drainage during the mining operation a displacement comparison method was adopted to measure the dilated amount of protected coal seams and as expected the maximum dilation percentage was much more than 0 2 the critical value upon which the target coal seam is appropriately depressurized to allow gas drainage to be safely and effectively implemented

highly varying radiogenic heat production in finland fennoscandian shield abstract radiogenic heat production in finland has been previously studied using airborne gamma ray surveys and glacial till measurements alike for the first time this paper presents a detailed survey on the spatial variation in radiogenic heat production determined using outcrop samples obtained from all important lithologies of the country the dataset of 6465 samples represents mostly mesoarchean about 2 7 ga paleoproterozoic ca 2 2 1 8 ga and mesoproterozoic ca 1 6 1 3 ga rocks nearly all data are from precambrian fennoscandian shield area but heat production appears to be highly variable and above global archean and proterozoic averages spot readings show an arithmetic average of 1 34 1 19 wm 3 and a range from 0 02 to 19 4 wm 3 the interpolated areal average of the whole area is 1 42 1 41 wm 3 the high standard deviation of data is related to the geochemical characteristics of uranium u thorium th and potassium k resulting in a skewed distribution of heat production mesoproterozoic anorogenic rapakivi granites and late paleoproterozoic svecofennian granitoids show the highest heat production values in the range of 3 5 wm 3 the results show no distinct dependencies of heat production with geological age metamorphic grade nor seismic p wave velocity but an increasing trend of heat production with sio2 content and decreasing trends of heat production with fe2o3 content and with rock density are evident surface heat flow 44 borehole data values correlates weakly with heat production r 0 35 the general heterogeneity of heat production calls for supporting information from other geophysical methods for better understanding of the thermal state of the lithosphere in finland and beyond

advanced techniques in site characterization and mining hazard detection for the underground coal industry abstract today s highly productive coal mining systems represent large capital investments careful geotechnical planning and design are essential to protect these systems and to help ensure their overall success too often however the ability of the mine operator to adequately characterize the geotechnical environment and keep up with changing geologic conditions lags the advance rate of the mining equipment seismic tomographic imaging based on the same principles as medical computer aided tomography cat scans offers the ability to identify changing geologic conditions loading patterns and the location of nearby abandoned mine workings although seismic tomography has been used for many years in the oil industry until recently its practicality in the mining industry has been limited because the processes involved interfered with mining productivity and were labor intensive in terms of data collection and interpretation new advancements in signal processing have greatly enhanced the speed resolution and range of applications of tomographic imaging in underground coal mine settings many tomography applications in the mining industry use seismic velocity and or attenuation tomography within a volume enclosed by the seismic source and receiver array although results obtained using this geometry work well in many situations recent developments in reflection tomography show promise in eliminating the requirement that the target volume be surrounded by sources receivers for example in seam seismic reflection tomography may now be used to image structures and or old workings from one general location in the mine e g face areas of mains and panel developments well ahead of planned developments largely eliminating the need to probe hole drill on regular intervals these new developments have greatly expanded the ability of the mine operator to cost effectively characterize previously inaccessible areas of the property this paper gives an overview of the theories and processes involved in seismic tomography applicable to coal mine settings recent examples are presented of tomographic imaging applied to a variety of coal mine ground control problems and old works detection in the united states and europe the applicability of both seismic refraction and seismic reflection tomography is discussed

petrology and geochemistry of mafic granulite xenoliths from the lahtojoki kimberlite pipe eastern finland abstract the lahtojoki kimberlite pipe in kaavi eastern finland contains lower crustal mafic granulite xenoliths with a mineral assemblage cpx amph pl grt opx bt the tweequ thermobarometry indicates crystallization at ca 800 900 c and 0 75 1 25 gpa which corresponds with crustal depths of ca 22 38 km reaction textures and results of thermobarometry in some xenoliths indicate post peak decompression with cooling chemical composition of the xenoliths suggest that their protoliths crystallized from basaltic melts with some k enrichment their ree patterns are slightly lree enriched some xenoliths having small negative eu anomalies the u pb ion probe dating of zircons from two samples yielded variable ages for zircons even in the same xenolith between ca 2 6 and 1 7 ga these ages correspond with main late archaean and palaeoproterozoic orogenic events in the fennoscandian shield the sm nd garnet clinopyroxene isochron age from one dated sample is 1 6 ga which represents either a cooling or reheating of the lower crust by rapakivi magmatism because the petrology geochemistry and ages of xenoliths do not correlate well with the nearest exposed archaean mafic granulites it is evident that the present lower crust underlying the archaean rocks has a considerable palaeoproterozoic component

a zoning model for coal mining induced strata movement based on microseismic monitoring a microseismic monitoring technique is adopted to investigate the distribution regularity of microseismic events released by the coal mining induced roof rock mass along the vertical and horizontal directions in combination with mine geological data on the basis of the quantity and energy distributions of the microseismic events recorded using the microseismic monitoring technique a zoning method is first established for the roof strata movement in the vertical and horizontal directions the vertically zoning method is then applied to analyze the microseismic monitoring results obtained in the dongjiahe coal mine which divides rock mass into six zones along the vertical direction i e the caved zone the block zone the vertical fracture through going zone the vertical fracture zone the separation zone and the continuous zone the horizontally zoning model divides the roof strata movement into three zones i e the calm zone the generation zone impacted by working face and the historical generation zone after that based on the horizontally zoning model a method is developed to determine the displacement angle using the microseismic monitoring data which has been verified in the dongjiahe coal mine

overview on the application of geophysics in coal mining abstract since their introduction to the coal mining industries of the united kingdom and west germany in the 1970s geophysical methods are now utilised in coal mining around the world the range of applications in both surface and underground mining is extensive applications include coal seam mapping and geological fault detection lithological mapping geotechnical evaluation assessment of the rock mass response to mining detection of voids location of trapped miners and guidance of drills and mining equipment the range of techniques that can be employed is also extensive and includes geophysical borehole logging the potential field methods seismic reflection 2d and 3d resistivity electromagnetics and microseismic monitoring using active and passive sources this paper discusses the major applications and the geophysical methods that can be applied it also discusses future trends and suggests that the future motives for applying geophysics will not only include the current motivations of mine safety and productivity but will also include an increased emphasis on environmental management the monitoring of sequestration activities and the provision of sensors to enable autonomous mining

physical modelling of subsidence from sequential extraction of partially overlapping longwall panels and study of substrata movement characteristics field examples of subsidence from sequential extraction of overlapping coal longwall panels have shown that complex and unexpected subsidence effects can occur physical models comprising sand and plaster obeying relevant similarity rules were used to investigate the subsidence mechanisms displacements within the models were measured using a combination of optical transducers photogrammetry and laser scanning the observed results were compared with finite element models the models demonstrate that the incremental subsidence and substrata movement profiles after lower seam extraction can be separated into three different zones these zones undergo different horizontal and vertical movement characteristics the zone of overlap of the two longwall panels undergoes greater total subsidence compared to a single seam of equivalent thickness the limit angle of the subsidence also differs at the two ends of the lower extraction as a result of the effects of the previously mined out area above

a heat production model of a shield area and its implications for the heat flow heat production relationship the pikwitonei and sachigo subprovinces of central manitoba provide a cross sectional view of the superior province crust to constrain thermal models of the crust we measured heat production and thermal conductivity in rocks from this terrain using standard gamma ray spectrometry and divided bar techniques these data when used in a two dimensional model of shield crust show that estimates of surface heat flow and surface heat production yield the well known linear relationship between surface heat production and surface heat flow observed for heat flow provinces this demonstrates that determinations of heat production with depth based on inversion of the linear heat production heat flow relationship are non unique

an estimation method for cover pressure re establishment distance and pressure distribution in the goaf of longwall coal mines measurement of deformations and stresses in the goaf of longwall panels is difficult due to the inaccessibility of the waste area this paper proposes a method for estimating the distance to return of the cover pressure and the stress distribution in the goaf of flat lying longwall panels where the caving is bulking controlled in the development of the method it has been considered that the final subsidence on the surface is a result of deformation of the caved material and deformation of the strata over the caved zone i e during both the caving and the compaction of the caved material in this respect the stress strain behaviour of the caved rock pile bending of the lowest uncaved strata depending on seam thickness and residual expansion of fractured strata vertically over the caved zone have been described by using previous field and laboratory investigations from the relations established between these parameters and surface subsidence the re establishment of cover pressure distance has been characterised with a three parameter power function in which the independent variables are depth excavation height bulking factor and compressive strength of the rock fragments it has been found that the cover pressure distance increases exponentially by increasing depth unlike previous findings of investigations in which the cover pressure distance increases as a linear function of depth on the other hand the cover pressure distance for a constant depth and mining height increases if the bulking factor of the rock pile increases and or the strength of rock fragments decreases when the mining height increases the bulking factor of the caved rock pile increases and hence this result with increase in cover pressure distance an estimation of the stress distribution curve for panels which are wide enough for the development of cover pressure has been expressed with a six parameter taylor series polynomial function the general form of the stress development curves found from the proposed method has been verified with curves obtained through numerical models

inversion of seepage channels based on mining induced microseismic data abstract water inrush in mines has always been a major technical problem restricting the safe production of mines with abundant water seepage channels formed by fractures in rock masses provide the necessary conditions for water inrush to occur effectively controlling the formation of fractures in rock masses is essential for preventing water inrush disasters in response to the shortcomings of conventional water inrush monitoring methods a set of methods for the inversion of seepage channels in rock masses based on mining induced microseismic ms data was proposed in this paper a discrete fracture network dfn was built based on moment tensor mt theory and a method for extracting reasonable fractures associated with different failure mechanisms was proposed to enhance the applicability of the fractures derived from ms data ms derived fractures the ms derived fractures were transformed into a graph structure by graph theory subsequently the hydraulic properties of each node and edge in the graph structure were obtained based on darcy s law in addition the fluid flow time in the ms derived fractures was weighted to detect the shortest seepage channel finally the method was applied to a mine that experienced a water inrush disaster the seepage channel formation process water pressure distribution and main seepage channel in the study area of the mine were analyzed the results may provide references for decision makers regarding when and where to implement water shutoff measures in mines

microseismic investigation of mining induced brittle fault activation in a chinese coal mine abstract the process whereby a brittle fault was activated by mining is not only significant for disaster prediction but also for earthquake prediction thus it was necessary to study their activation process in this study stress state ae acoustic emission ms microseismic activities during brittle fault activation stages of brittle fault activation and the relation between ae ms activities and brittle fault parameters were analysed and it was feasible to identify buried brittle faults determine their parameters and activation process based on ms monitoring the no 22517 working face in the dongjiahe coalmine was taken as an example firstly a buried brittle fault was identified in no 22517 working face by the ms monitoring method secondly the buried brittle fault parameters were determined its azimuth angle was 307 5 in the orbital roadway and 357 5 on the haulage roadway its dip angle was 73 and it was a reverse fault thirdly the activation process of the buried brittle fault was determined the buried brittle fault was not affected by the mining activities when the distance from mining activities to the buried brittle fault was over 300 m the disturbance stage was from 300 m to 80 m and the local activation stage from 100 m to 30 m and the whole activation stage around 30 m the b value decreased during the process of brittle fault activation and reached a minimum value at the whole activation stage it was concluded that these changes are related to the stress distribution around the brittle fault the results demonstrated that ms monitoring technology can detect small buried brittle faults ahead of the working face and is also an effective method to study the process and mechanism of brittle fault activation

terrestrial heat flow and groundwater circulation in the bedrock in the central baltic shield abstract unpublished heat flow measurements from 17 drillholes in finland central baltic shield are presented the holes range from 270 to 1080 m in depth sharp vertical changes in the heat flow density and in the temperature gradient indicating groundwater flow disturbances were detected in eight holes the variations in heat flow were typically of the order of 5 10 mw m 2 in many cases the groundwater flow concept was supported by geological logs and other borehole measurements which indicated the existence of fracture zones at the same depths as the flow the flow zones were usually encountered at depths of less than 500 m but flows between fracture zones in the holes were detected even deeper at as much as 930 m according to recent groundwater studies in the same holes the water flowing in the fracture zones seems to be fresh or only slightly saline in composition this can be taken as an indication of relatively rapidly circulating groundwater in contrast to the more saline and more stagnant groundwater encountered deeper in the holes the results indicate that disturbances in heat flow induced by groundwater flow may be much more common in areas of crystalline bedrock than has previously been realized the apparent heat flow densities mean 35 0 3 0 mw m 2 agree well with values published previously from the central baltic shield but the results from southern and western finland indicate regionally above average heat flow values 45 mw m 2

modelling of strata movement with a special reference to caving mechanism in thick seam coal mining abstract caving of top coal behind the face is the key factor affecting the efficiency of production at thick coal seams during production of top coal by caving behind the face not only is a significant amount of coal lost in the goaf but also the coal drawn by means of caving is usually diluted considerably with surrounding rock therefore it is not possible to carry out an efficient production operation unless caving of top coal behind the face is optimized in this paper results of 3 d modelling of the top coal caving mechanism at the m3 longwall panel of omerler underground mine located at tuncbilek turkey are presented by using a finite difference code called flac 3d according to modelling results a 1 5 2 0 m thick layer of coal just above the shield supports is well fractured however 3 0 3 5 m thick layer of coal above the well fractured part is either not fractured or fractured in the form of large blocks leading to obstruction of windows of shields during coal drawing it is concluded that in order to decrease dilution and increase extraction ratio and production efficiency the top coal should be as uniformly fractured as much as possible hence an efficient and continuous coal flowing behind the face can be maintained a special pre fracture blasting strategy just sufficient enough to form cracks in the top coal is suggested by means of comparing results from numerical modelling

finite element modeling of stress distributions and problems for multi slice longwall mining in bangladesh with special reference to the barapukuria coal mine abstract this paper deals with current coal mining operations under a mega aquifer in nw bangladesh and presents a case study of underground mining in barapukuria the study uses numerical analyses to evaluate stress redistribution strata failure and water inflow enhancements that result from these coal extraction operations a total of three models a b and c are presented in this study two dimensional numerical modeling was performed to analyze the deformation and failure behavior of rock elements for two different models a and b for model a we used an elastic finite element software package considering a mohr coulomb failure criterion for model b we used boundary element method bem the first two models were applied to determine the stress patterns model a provides the tectonic stress pattern of the basin whereas model b represents the mining induced stress field the third model is a schematic model the results of model a show that tensional failure of rock elements is concentrated in the gondwana coal sequences as well as within the eastern boundary fault ebf and its surroundings failure occurs in the middle to lower part of the model and the magnitude of tensional stress in the shallow part is much greater than in the deeper part contours of max magnitudes are attributed to up bending of the overburden which would create numerous upward propagating fissures fractures the results of model b show that fracture propagation would be about 240 m upward for single slice height 3 m mining extraction from the contours of mean stress magnitudes it is observed that the high range of fracture propagation increased upward for multi slice extraction of coal it is apparent from the fracture heights that large amounts of caving would occur towards the roof due to the multi slice extraction of coal and finally would be linked with the water bearing dupi tila formation if this happened it would ultimately cause a major water inflow hazard in the mine

lithological interpretation of crustal composition in the fennoscandian shield with seismic velocity data abstract in this study we report the results of an investigation of lithological interpretation of the crust in the central fennoscandian shield in finland using seismic wide angle velocity models and laboratory measurements on p and s wave velocities of different rock types the velocities adopted from wide angle velocity models were compared with laboratory velocities of different rock types corrected for the crustal pt conditions in the study area the wide angle velocity models indicate that the p wave velocity does not only increase step wise at boundaries of major crustal layers but there is also gradual increase of velocity within the layers on the other hand the laboratory measurements of velocities indicate that no single rock type is able to provide the gradual downward increasing trends thus there must be gradual vertical changes in rock composition the downward increase of velocities indicates that the composition of the crust becomes gradually more mafic with increasing depth we have calculated vertical velocity profiles for a range of possible crustal lithological compositions the finnish crustal velocity profiles require a more mafic composition than an average global continental model would suggest for instance on the sveka 81 transect the calculated models suggest that the crustal velocity profiles can be simulated with rock type mixtures where the upper crust consists of felsic gneisses and granitic granodioritic rocks with a minor contribution of amphibolite and diabase in the middle crust the amphibolite proportion increases the lower crust consists of tonalitic gneiss mafic garnet granulite hornblendite pyroxenite and minor mafic eclogite assuming that these rock types are present in sufficiently extensive and thick layers they would also have sufficiently high acoustic reflection coefficients for generating the generally well developed reflectivity in the crust in the central part of the shield density profiles calculated from the lithological models suggest that there is practically no density contrast at moho in areas of the high velocity lower crust comparison of reflectors from fire 1 and fire 3 transects and the velocity model from sveka 81 wide angle transect indicated that the reflectors correlate with velocity layering but the three dimensional structures of the crust complicate such comparisons

horizontal stress under supercritical longwall panels abstract this study identifies the relative magnitude of horizontal stress change below a series of parallel longwall panels as a consequence of multi seam mining the investigation method yields an upper bound to the horizontal stress change by assuming that the fractured and caved overburden above the supercritical longwall panels is not able to support any lateral load finite element modelling was conducted to consider the effects of the following variables on the horizontal stress redistribution the ratio of the equivalent width of the extracted area to the overburden depth the ratio of the original horizontal to vertical in situ stress components and anisotropy in the rock mass behaviour the key findings of this research are that the maximum horizontal stress induced as a consequence of extracting multiple supercritical longwall panels will be within approximately 10 of the original in situ horizontal stress for the case of isotropic rock strata the magnitude of this horizontal stress may be larger in a stiff stratum if the overall sequence of strata consists predominantly of softer rocks anisotropy in the strata underlying the extracted longwall panels also causes an increase in the maximum horizontal stress induced into the immediate floor of the first extracted seam and an increase in the rate of dissipation of horizontal stress change with depth these findings indicate that a significant increase in horizontal stress relative to the original in situ horizontal stress should not be expected in multi seam mining situations the results from this study need to be considered in conjunction with predicted vertical stress distributions in order to accurately predict the overall stress environment likely to be encountered when conducting multi seam mining

investigation of movement and damage of integral overburden during shallow coal seam mining abstract most prediction methods used to calculate mining induced subsidence are empirical which cannot explain the mechanism of fundamental rock strata movement in this paper based on key stratum theory and the mechanical analysis of overburden a new analytical solution the analogous hyperbola subsidence model ahsm was proposed to describe the movement and damage of inner burden mining induced rock strata movement was verified using the distinct element method udec to assess the performance of the theoretical model three subsidence parameters smax t sgoaf smax d h generally used to describe surface subsidence trough agree with statistical field measurements of the south coalfield in australia the surface subsidence and the movement boundary in the overburden are very close to the theoretical predictions additionally the primary key stratum damages the least in the overlying strata its broken length is the smallest the width of subsidence trough and maximum surface subsidence increase as the primary key stratum drops

assessment of rock mass characteristics and the excavation disturbed zone in the lingxin coal mine beneath the xitian river china safe production and induced hazard prevention in coal mines mainly concern problems in the excavation disturbed zone edz but coal mining can also make a significant impact on the environment comprehensive techniques using a borehole tv viewer system electrical logging and monitoring of drilling fluid leakage offer the ability to identify changing geological conditions and the location of any nearby abandoned mining workings the inner collapsed zone and the expanding height of the crack zone transmitting water plus their spatial distribution after excavating the superincumbent coal seam stratum are determined at no l3414 workings lingxin coal mine beneath the xitian river china an integrated system of gis based on a stochastic model which has been developed for the prediction of dynamic subsidence coupling the time function and probabilistic integral method is verified through practice at the lingxin coal mine this development has greatly expanded the ability of the mine operator to characterize previously inaccessible areas of the mine providing a reliable basis for safe mining and prevention of induced hazards to ensure high production mining underneath the river bed

mining induced seismicity seismic measurement using multiplet approach and numerical modeling the volume of influence of mining works is essentially determined from in situ observations field measurements particularly surface subsidence measurements as well as from numerical investigations seismic monitoring is the primary requirement for mining in rock burst environment a micro seismic network is systematically used to monitor coal extraction in the provence colliery south eastern france a significant database of seismic events is now available a further advancement in this sequence was added by the development of doublets technique or multiplet selections the technique uses with the database to identify families of seismic events and to work out the relative locations of these events the analysis of location of these multiplet families showed a particular spatial distribution locations of the epicentre follow the direction in which the coalface is advancing numerical models are used in the paper to show the overstress distribution by comparing the seismic activity and results of the numerical modeling of the advancing coalface with observations a close correlation can be established between the location of seismic activity and induced stresses in the ground surface of the working areas by combining micro seismic monitoring with the numerical modeling the volume of influence of long wall mines is determined results show that such a coupling can be an efficient way for detecting areas subjected to rock burst hazards this can also prove to be a powerful tool for assisting the planning of underground workings in complex geological and mining conditions

numerical modelling of microseismicity associated with longwall coal mining abstract microseismicity has long been a precursor for underground mining hazards such as rockbursts and coal and gas outbursts in this research a methodology combining deterministic stress and failure analysis and stochastic fracture slip evaluation based upon the widely accepted fracture slip seismicity generation mechanism has been developed to simulate microseismic events induced by longwall mining using the built in dfn facility in flac3d discrete fractures following a power law size distribution are distributed throughout a 3d continuum model in a probabilistic way to account for the stochastic nature of microseismicity the dfn based modelling approach developed was adopted to simulate the evolution of microseismicity induced by the progressive face advance in a longwall top coal caving ltcc panel at coal mine velenje slovenia at each excavation step global stress and failure analysis with reference to the strain softening post failure behaviour characteristic of coal and fracture slip evaluation for microseismicity are conducted sequentially the model findings are compared to the microseismic event data recorded during a long term field monitoring campaign conducted at the same ltcc panel it was found that the released energy and frequency magnitude distribution of microseismicity are associated with the slipped fracture sizes and fracture size distribution these features for recorded microseismic events were fairly constant until a xylite rich heterogeneous zone ahead of the working face was approached which indicates that fractures within the extracted coal seam follow the same size distribution the features obtained from modelled microseismic events were consistent over the production period and matched well the field observations furthermore the model results indicate that the power law fracture size distribution can be used to model longwall mining induced microseismicity this model provides a unique prospective to understand longwall coal mining induced microseismicity and lays a foundation to predict microseismicity or even rockburst potential in specific geological realisations

acoustic emission and thermal infrared precursors associated with bump prone coal failure abstract coal bump is sudden catastrophic failure of coal and usually causes serious problems to underground coal mining the acoustic and thermal infrared radiation tir characteristics of bump prone coal under uniaxial compression and cyclic loading conditions are investigated in this study the monitoring system consists of a tir observation system a stress and strain measurement system and an acoustic emission monitoring system precursory information for impending failure of coal samples is collected including tir acoustic emission and strain precursors moreover the response speed and the sensitivity of different monitoring systems during the cracking events in the samples are studied under different loading conditions the microstructure of coal sample is analyzed by x ray computerized tomography ct and scanning electron microscope sem the experiment results show that 0 9 c c is the compressive strength and 0 82 c can be regarded as the stress caution points for the failure of bump prone coal under uniaxial compression and under uniaxial cyclic compression respectively they are much higher than 0 79 c as the stress caution point for the normal coal samples it is also indicated that the temperature at coal surface or in the coal mass should be monitored at the perimeter of the site with anticipated collapses it can be a valuable tool to obtain the precursors for mine disaster control such as coal bumps gas outburst and water inrush

formation of fractured zones in overburden due to longwall mining the fractured zones caused by mining were studied in the overburden of the torezko snezhnyanskaya area ukraine through the change in natural gas emission from these zones during longwall coal excavation zones of interconnected fractures and separate horizontal fractures were studied with vertical wells drilled from the ground surface down to active underground workings the maximum heights of the zone of interconnected fractures and separate horizontal fractures may reach 19 41 and 53 92 times the thickness of the coal seam respectively it was found that the ratio between the maximum height of the zone of interconnected fractures and the thickness of the extracted coal seam increases with the increasing number of rock layer interfaces and decreases with the increasing stiffness of immediate roof it is shown that the growth of the zone of interconnected fractures occurred during 17 39 days at an average rate of 0 94 1 97 m day 1 and it was accompanied by increasing methane emission from overburden observation shows that the formation of separate horizontal fractures began only 11 49 5 days after the height of the zone of interconnected fractures reached its maximum value formation of separate horizontal fractures in overburden over the longwall excavation occurred as a stepped process from lower to upper sandstone sandy shale layer interfaces in the direction of the ground surface

the kola alkaline province of the cis and finland precise rbsr ages define 380 360 ma age range for all magmatism abstract twenty one new rb sr mineral and biotite whole rock isochrons are presented for intrusive rock complexes of the palaeozoic kola alkaline province in the cis and finland samples from the ultrabasic alkaline and nepheline syenite complexes khibina lovozero afrikanda turiy mys ozernaya varaka sokli and iivaara all yield ages in the very narrow range from 361 7 to 377 3 ma i e late middle devonian to upper devonian these data represent crystallization rather than intrusion ages but are nevertheless argued as marking very closely the time of intrusion there is no indication of bimodal age distribution the emplacement of the alkaline magmas is related temporally to the subsidence of the kontozero graben of the central kola peninsula sr initial ratios of the agpaitic nepheline syenites of the giant khibina and lovozero intrusions scatter between 0 703 and 0 704 because of high rb sr ratios of the rocks these isotope ratios exclude long term pre enrichment of alkalis in the sources of the magmas prior to segregation and intrusion and thus episodic enrichment during earlier rifting events in the northern baltic shield the magma formation may be related to wrench movements in the surroundings of the major trollfjord komagelv fault which forms part of the late caledonian arctic north atlantic megashear system

seismic monitoring and analysis of excessive gas emissions in heterogeneous coal seams abstract uncontrolled and excessive gas emissions pose a serious threat to safety in underground coal mining in a recently completed research project a suite of monitoring techniques were employed to assess the dynamic response of the coal seam being mined to longwall face advance at coal mine velenje in slovenia together with continuous monitoring of gas emissions two seismic tomography measurement campaigns and a microseismic monitoring programme were implemented at one longwall top coal caving panel over 2000 microseismic events were recorded during a period of four months over the same period there also was a recorded episode of relatively high gas emission in the same longwall district in this paper a detailed analysis of the processed microseismic data collected during the same monitoring period is presented specifically the analysis includes the spatial distribution of the microseismic events with respect to the longwall face advance the magnitude of the energy released per week and its temporal evolution examination of the spatial distribution of the recorded microseismic events has shown that most of the microseismic activity occurred ahead of the advancing face furthermore the analysis of the gas emission and microseismic monitoring data has suggested that there is a direct correlation between microseismicity and gas emission rate and that gas emission rate tends to reach a peak when seismic energy increases dramatically it is believed that localised stress concentration over a relatively strong xylite rich zone and its eventual failure which was also identified by the seismic tomography measurements may have triggered the heightened microseismic activity and the excessive gas emission episode experienced at the longwall panel monitored

prediction of the height of destressed zone above the mined panel roof in longwall coal mining abstract longwall mining is one of the most widely used underground mining methods most suitable in relatively flat lying thick and uniform coalbeds due to extraction of the coal seam the panel roof strata above the mined zone will be destressed and then the roof loads will be redistributed and transferred to the front abutment and neighboring solid sections with higher load bearing capacity where the adjacent access tunnels and the corresponding barrier pillars are located the height of destressed zone hdz in this paper is taken as equivalent to the combined height of the caving and fracturing zones above the mined panel roof induced due to longwall mining the height of destressed zone plays a vital role in accurate determination of the amount of loads being transferred towards front abutment and panel sides the paper describes the mechanism of development of the height of this zone finally five new simple yet conclusive mathematical approaches to estimate the height of destressed zone are presented the results of the methods proposed are compared with each other and with the comparable methods the methods proposed are further compared and verified with in situ measurements reported in the literatures the comparative results confirm the agreement that exist among the methods and those with the in situ measurements as well finally the methods have shown that in short term the height of destressed zone ranges from 6 5 to 24 times the extraction coal seam height while in long term the height of destressed zone ranges from 11 5 to 46 5 times the extraction coal seam height therefore beyond this height the overburden pressure will be transferred towards the front abutment the adjacent access tunnels the intervening barrier pillars as well as the panel rib sides

in situ identification of water permeable fractured zone in overlying composite strata abstract the height and boundary shape of a water permeable fractured zone wfz play an important role in mining safety under challenging conditions for example when the coal seam is subject to a confined aquifer or the roadway is designed in close range to the coal seam for the accurate estimation of the wfz height the theoretical prediction method was introduced based on the overlying composite strata structure and an empirical equation in situ detection of the wfz height and shape was performed in the zhaizhen coal mine china the field detection was executed by injecting water into boreholes based on the analysis results of the variation in water seepage along these boreholes the fracture intensity and the permeability of the overlying strata were studied and the height and boundary shape of the wfz were also confirmed the measured height was consistent with the theoretical estimation verifying that the wfz developed upwards through the strata group acting as a unit the final boundary of the wfz presented an irregular saddle shape and the boundary angle was approximately 75 78 according to the height and shape of the wfz induced by mining of the lower coal seam the fracture intensity and scope of the surrounding rock and the mining feasibility of the upper coal seam was evaluated in the zhaizhen mine a suitable roadway layout of the upper coal seam was also designed

crustal heterogeneities and the thermal structure of the continental crust the observed linear relationship between surface heat flow q0 and the radiogenic heat production of near surface rocks a0 discovered almost two decades ago has been a primary tool used to infer the distribution of heat production in the continental crust recent evidence on the nature of compositional heterogeneities in the continental crust has led us to reexamine the q0 a0 relationship and the likely implications for the thermal structure of the lower continental crust numerical simulations of crustal thermal models indicate that some interpretations derived from this relation may be flawed in particular the length scale determined from the q0 a0 function normally thought to describe the depth distribution of crustal heat sources is significantly affected by the horizontal scale of crustal heterogeneity as a consequence most estimates of lower crustal heat flow and lower crustal temperatures obtained using heat flow data with the q0 a0 relationship are overestimates this overestimation is proportionally largest in areas of low mantle heat flux such as cratons where basal heat flux may be overestimated by more than a factor of two

heat flow map of northern and central parts of the fennoscandian shield based on geochemical surveys of heat producing elements abstract the heat flow heat production q a relationship is a useful tool in geothermal research and it has been widely used for delineating geothermal provinces and determining characteristic parameters of heat production in the continental crust in this study a simple but rarely used technique of utilizing the heat flow heat production relationship is discussed in central and northern parts of the fennoscandian shield extensive geochemical surveys have produced 1483 samples taken from glacial till with a sampling density of 1 sample 300 km 2 heat production values determined from u th and k concentrations in these samples were used to calculate a map of heat flow density a previously determined q a relationship q 15 8 10 8 a was applied the compiled map covers all finland northern sweden and northern norway about 35 of the exposed shield area in fennoscandia heat flow density and heat production increase with decreasing geological age and correlate with granitoid types the calculated heat flow density values on the map were controlled with 12 drill hole measurements not used in calculating the applied q a regression line nine of them are from previously unpublished data from the finnish part of the shield the agreement with drill hole measurements and the geochemical estimate is reasonable although not perfect in all cases the differences can be attributed to anomalous vertical variation in heat production reliability of the applied q a plot reliability of till geochemistry in bedrock studies convective groundwater disturbances or local structural effects the calculated heat flow map can be used as a data set supplementing drill hole measurements to determine representative values of heat flow density in areas with low numbers of drill hole measurements

terrestrial heat flow and radiogenic heat production in finland the central baltic shield abstract heat flow density and radiogenic heat production of the bedrock were studied in finland in part of the central baltic fennoscandian shield heat flow data were collected from 35 holes 270 1080 m deep the heat production values at the sites were determined from the drill core samples by gamma ray spectrometry the areal variation in heat production was studied with the aid of k u and th analyses of 1054 glacial till samples collected for the geochemical atlas of finland a heat production map constructed from this data set revealed a strong areal variation that can be attributed to the known lithological geochemical and tectonic features of the bedrock in general heat production seems to increase with decreasing geological age the presented data strongly suggest that the southern and western parts of finland are geothermally anomalous apparent heat flow density 38 68 mw m 2 surface heat production 2 0 w m 3 in contrast to the other parts of the country mw m 2 w m 3 the heat production heat flow density plots were constructed from apparent and palaeoclimatically corrected heat flow densities the heat production values were determined from both drill core samples and till samples the plot constructed from the till data and apparent heat flow densities which yielded a scale depth of 10 8 2 6 km and a reduced heat flow density of 15 8 4 9 mw m 2 was considered the most reliable the results are discussed in terms of crustal fracturing and deep groundwater flow if the crystalline bedrock is approached as a medium consisting of blocks internally conductive but bounded by fracture zones in which heat is transported by groundwater flow an alternative hypothesis can be constructed for interpreting the linear heat production heat flow density plots according to this hypothesis the scale depth and reduced heat flow densities refer only to the geothermal properties of the uppermost bedrock block in the present study this concept is supported by results from deep electromagnetic and seismic soundings

paleotectonics and hydrocarbon accumulation powder river basin wyoming the belle fourche arch a subtle northeast trending paleoarch extends across the central part of the powder river basin wyoming to the black hills uplift the arch is the result of differential vertical uplift primarily during cretaceous time on numerous northeast trending structural lineaments lineament trends are identified from structural offsets in the black hills monocline offsets in well defined linear topographic escarpments and by linear drainages which connect trends between the monocline and the escarpments underlying basement zones of weakness are thought to be shear zones of precambrian age analogous to the mullen creek nash fork shear zone of southeast wyoming stratigraphic evidence suggests that the structural lineaments which form the belle fourch arch have rejuvenated periodically throughout the phanerozoic subtle movements along the lineaments have affected depositional environments and hydrocarbon accumulation in virtually all significant reservoirs in the northern two thirds of the basin evidence includes 1 localization of minnelusa formation permian hydrocarbon production along the crest of the arch 2 localization of dakota formation cretaceous alluvial point bar production on the crest of the arch 3 localization of lower muddy formation cretaceous channel deposits parallel with and on the downthrown sides of lineament trends 4 abrupt change in depositional strike of upper muddy formation cretaceous marine bars close to the arch 5 superposition of turner sandstone cretaceous channel deposits alon the trends of muddy channels and 6 localization of virtually all significant upper cretaceous shannon and sussex sandstone offshore marine bar production along the crest of the arch subtle uplift along the arch was persistent during at least lower muddy through sussex deposition a period of about 35 m y