sediment dewatering in the makran accretionary prism abstract sediments within the makran accretionary prism are considerably more compacted than the material entering the subduction zone due to the additional tectonic stresses resulting from plate convergence and accretionary processes tectonic compaction of the offscraped sediments has been documented by deriving in situ porosities in the upper 4 km from their seismic velocities wide angle seismic reflection refraction profiles were analysed from a transect crossing both the makran accretionary prism and the undeformed abyssal plain sediments to the south the 6 7 km thick abyssal plain sediments exhibit normal compaction with depth the sediments incorporated into the accretionary prism have higher seismic velocities at all depths corresponding to reductions in porosity of 30 40 mapping the porosity depth gradient across the prism shows that there is a marked change in porosity at the seaward toe of the prism the frontal fold there is then little further change until further folding begins to occur 70 km landward of the toe the dewatering and consolidation of the sediments is an important control on deformation occurring within the sedimentary prism

a discontinuum modelling approach for investigation of longwall top coal caving mechanisms abstract this paper presents a discontinuum modelling approach to investigate longwall top coal caving ltcc behaviour including stress distribution coal and rock failures top coal caving and roof strata rupture and to analyse the impact of overburden movement on top coal caving the current model ia successful in using plastic material in a discontinuum code for intact rocks the model scale is large enough to capture the critical features of ltcc including steady state caving of top coal and repeatable periodic weighting of roof strata the applicability of the numerical model was assessed by calibration with field measurements obtained from a longwall mine site the numerical study found that the stress distribution caused by ltcc mining is in general similar to that caused by conventional longwall mining top coal predominantly fails in shear whereas roof rock mostly fails in tension top coal starts to cave in stress caving while main roof strata first rupture in crushing mode and roof strata weightings periodically increase and decrease top coal cavability the findings of this study should assist engineers in better understanding fundamental rock mechanics associated with ltcc identifying key geotechnical parameters dominating caving behaviour and managing top coal productivity and mine safety involved in ltcc operation

controls on terrigenous sediment supply to the arabian sea during the late quaternary the makran continental slope the input of terrigenous sediment along the tectonically active makran continental margin off south western pakistan gulf of oman northern arabian sea is studied on the basis of sediment cores distributed along a transect from the upper slope to the abyssal plain spatial and temporal variations in sediment composition sedimentation rate and turbidite frequency in late pleistocene holocene time last 20 14c ka will be discussed and related to changes in sea level and climate and tectonic activity end member modelling of the grain size distributions of the hemipelagic and turbiditic sediments indicate that the sediments are adequately described as mixtures of three end members which represent turbidite sand turbidite silt or eolian dust and fluvial mud the geochemical and mineralogical compositions of the hemipelagic sediments indicate that the eolian dust was dominantly supplied from the northern arabian peninsula and the persian gulf region and that the fluvial input is from the makran margin the ratio of contributions of eolian and fluvial sediment in the hemipelagic intervals is used as an indicator of continental aridity i e summer monsoon intensity highest holocene turbidite frequencies and sedimentation rates are recorded at the deepest coring sites they are related to the proximity of the deformation front of the accretionary prism turbidite sedimentation on the upper continental slope was most frequent during the last glacial period of sea level lowstand and continued during the entire deglaciation and sea level rise infrequent turbidite sedimentation occurred during the holocene highstand of sea level turbidite sedimentation during the period of late sea level rise and the holocene sea level highstand is inferred to be due to the strong impact of episodic events i e flash floods and earthquakes and because of the narrow shelf of the active makran continental margin

temporal variability in the northern arabian sea oxygen minimum zone omz during the last 225 000 years the northern arabian sea is one of the few regions in the open ocean where thermocline water is severely depleted in oxygen the intensity of this oxygen minimum zone omz has been reconstructed over the past 225 000 years using proxies for surface water productivity water column denitrification winter mixing and the aragonite compensation depth acd changes in omz intensity occurred on orbital and suborbital timescales lowest o2 levels correlate with productivity maxima and shallow winter mixing precession related productivity maxima lag early summer insolation maxima by 6 kyr which we attribute to a prolonged summer monsoon season related to higher insolation at the end of the summer periods with a weakened or even non existent omz are characterized by low productivity conditions and deep winter mixing attributed to strong and cold winter monsoonal winds the timing of deep winter mixing events corresponds with that of periods of climatic cooling in the north atlantic region

close in scs and sscs reverberations from the 9 june 1994 bolivian earthquake recordings of the bolivian earthquake of 9 june 1994 from two portable experiments were analyzed for scs and sscs reverberations these stations span the distance range 6 22 sampling the mantle beneath south america along an ew line from the central andes to the brazilian craton we used the core method to obtain path averaged locations of the moho and 400 and 660 km discontinuities the average depth for d400 is 410km for the banjo stations and 395km beneath brazil and the value for d660 is 700km for banjo and 675km for blsp while the difference d660 d400 d is 290km and 280km respectively these values are much larger than the global average around 245km and suggest 200 300 colder temperatures in the region sampled this is most plausibly explained by the reduced temperatures in the slab and surrounding region we also detect a significant discontinuity at 210 km depth with a shear wave impedance increase of at least 5 finally we observe systematic variations in duration between p scs and sscs that can only be attributed to source finiteness these observations constrain the inclination of an equivalent unilateral rupture velocity vector to be 17 positive up from horizontal our rupture model is consistent with models derived from subevent analysis of the p wave arrivals and implies a source extent of 72 km

electric potential changes prior to shear fracture in dry and saturated rocks electric potential changes before shear rupture were measured using darley dale sandstone quartz rich and icelandic basalt quartz free on both dry specimens and in the presence of pore fluid we find that electric potential changed markedly just prior to dynamic rupture in dry and saturated sandstones and saturated basalt but we did not detect precursory signals in dry basalt the absence of signals in dry basalt provides strong evidence that the piezoelectric effect and electrokinetic effect are dominant sources for precursory signals moreover we find that the amplitude of the precursory signals due to electrokinetic effect in saturated sandstone were as large as the coseismic signals we propose that this signal is caused by accelerating evolution of dilatancy as cracks grow in the rock before rupture resulting in water flow into the dilatant region with an electric current produced concurrently

introduction to the special issue gis based mineral potential modelling and geological data analyses for mineral exploration this introduction provides an overview of the procedures involved in mineral potential modelling the papers included in this special issue are also summarized

experimental study on damage failure mechanical characteristics and crack evolution of water bearing surrounding rock water plays an important role in the mechanical properties of roadway surrounding rocks and poses a great threat to their stability to study the damage and failure characteristics and the fracture development laws of surrounding rock a uniaxial compression test for prefabricated fractures in water bearing surrounding rock was carried out results indicate that water bearing prefabricated fracture specimens are in better development condition after failure in water bearing specimens the propagation direction is more complex there are more secondary fissures and the fracture strength is significantly lower than in dry specimens when immersed in water the interior structure of surrounding rock is weakened and softened thus the intensity is reduced and the development and propagation of fractures is promoted for larger angles of the prefabricated fractures the compression failure of surrounding rock changes into shear failure as the angles approach 90 the shear failure again prevails therefore the strength of the surrounding rock firstly decreases and then increases a new ultimate stress strength model is developed for fractures caused by shear slip failure in water bearing surrounding rock the model results are consistent with the experimental results and the validity of the model is verified these results are helpful for deeply understanding the failure process of water bearing surrounding rock with prefabricated fractures the proposed model could be used for the evaluation of water bearing surrounding rock stability in coal mines as well as dynamic risk monitoring

electric potential source localization reveals a borehole leak during hydraulic fracturing abstracta laboratory experiment was performed to see if passively recorded electric signals can be inverted to retrieve the position of fluid leakages along a well during an attempt to hydraulically fracture a porous block in the laboratory the cubic block was instrumented with 32 nonpolarizing sintered ag agcl electrodes during the test several events were detected corresponding to fluid leakoff along the seal of the well each event showed a quick burst in the electric field followed by an exponential type relaxation of the potential distribution over time the occurrence of these electric events was always correlated with a burst in the acoustic emissions and a change in the fluid pressure these self potential data were inverted in two steps 1 using a deterministic least square algorithm with focusing to retrieve the position of the source current density in the block for a given snapshot in the electric potential distribution and 2 using a genetic algorithm to refine the position of the sou

analysis of roof fall hazards and risk assessment for zonguldak coal basin underground mines the roof fall hazards are frequent problems of underground coal mines which are generally unpredictable due to the associated uncertainties these uncertainties which arise from geological and stress conditions and mine environment make the control of roof fall hazards difficult in underground coal mines the most efficient method for coping with uncertainties in roof fall hazards is the use of risk assessment techniques in this study a risk assessment and management methodology is proposed for roof fall hazards in underground mines of the zonguldak coal basin the annual rates of roof falls obtained from the five mines in the basin are statistically analyzed the components of risk which are the probability of roof fall and consequences of roof fall hazard are identified and quantified the probability of roof fall is computed by fitting a distribution function to the annual roof fall while the consequences of roof falls are quantified based on a cost model then a decision analysis methodology for evaluating the performance of possible alternative action to be taken in order to decrease the risk is developed the results show that the underground coal mines in the zonguldak coal basin have considerably high risk levels and hence require comprehensive risk management schemes

astronomically induced paleoclimatic oscillations reflected in pliocene turbidite deposits on corfu greece implications for the interpretation of higher order cyclicity in ancient turbidite systems the growth pattern of fan lobes in the early pliocene corfu turbidite system greece demonstrates that regional climatic fluctuations in the land locked mediterranean completely concealed global glacioeustatic effects the temporal evolution of the fan lobes studied closely matches the astronomical precession cycle in this time interval 23 ka strongly suggesting that regular waxing and waning of the sediment supply to the delta fed turbidite system were directly driven by changes of precipitation and continental runoff the common lack of high resolution time control in ancient turbidite systems may lead to mistaken interpretations of higher order cyclicity in ancient turbidite sequences produced by precession induced variations of sediment supply at low paleolatitudes

atmospheric summer circulation and coastal upwelling in the arabian sea during the holocene and the last glaciation accumulation rates of biogenic and lithogenic components were studied in 39 turbidite free well dated sediment cores from the northern indian ocean to define the proportions of fluvial and eolian input and to reconstruct quaternary patterns of coastal upwelling the majority of dust deposited in the western arabian sea during the holocene about 100 106 t yr 1 is advected from arabia by northwesterly winds which overlie the low level southwest monsoon the glacial increase in dust flux to 160 106 t yr 1 culminated in the northern arabian sea most probably due to i entrainment of dust rich in chlorite dolomite and lithogenic carbonate in the then dry persian gulf and ii a southward shift of the mean position of the southwest monsoon during glacial summer this shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off somalia and oman both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27 000 yr as well as the asian continental summer heat low however the glacial seasonal time span of the southwest monsoon season was much reduced most likely because of a delay in the seasonal onset of the southwest monsoon

2d self potential tomographies for studying groundwater flows in the varco d izzo landslide basilicata southern italy abstract a geoelectrical monitoring activity has been carried out to improve the geological and hydrogeological knowledge about the varco d izzo landslide potenza basilicata southern apennine italy an active rotational translational slide evolved in earth flow in this work we have focused on the self potential sp method by applying three different sp measuring techniques and combining modern technologies for data acquisition and new methods for tomographic inversion a sp map and three static sp tomographies have been carried out to better analyse the groundwater circulation system and to better reconstruct the geometry of the landslide body in the accumulation zone which is the area more exposed to the geomorphological activity a new sp measuring strategy has been applied this strategy based on time continuous 2d sp tomographies helps identify water flow changes in subsurface by studying the time series of sp tomographic images the analysis of time dependent changes of water infiltration in near surface is the key to better understand the hydrogeological processes underlying the ground instability phenomena the time lapse analysis of tomographic images has allowed us not only to investigate the correlation between the temporal changes of sp signals and rainfall events but also to quantify the range of these changes the modification of the distribution of the sp source accumulation zones is associated with the dynamics of the groundwater flows these preliminary results allow us to consider the sp tomographic method as a tool for geophysical monitoring of landslide areas and encourage to develop new measuring systems for near real time applications

particle swarm optimization inversion of self potential data for depth estimation of coal fires over east basuria colliery jharia coalfield india coal fires pose a serious threat to the environment and it is important to detect them at an early stage for their control and hazard mitigation the present study addresses an innovative approach for depth estimation of coal fires using self potential sp method and its inversion through particle swarm optimization pso technique the suitability of pso inversion technique for self potential data has been established using synthetic models of spherical and cylindrical objects and inclined sheet with large horizontal extent as causative sources present study reveals that the geometry of subsurface coal combustion is possibly similar to inclined sheet with relatively large horizontal extension the depth of coal fires has been estimated using pso inversion of sp anomaly data over the east basuria colliery jharia coal field jharkhand india with good accuracy the results of the analysis are compared with borehole lithologic log data which proves efficacy of the pso inversion technique

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

hydraulic stimulation of geothermal reservoirs fluid flow electric potential and microseismicity relationships summary we have observed surface electric potential variations of several mv during a reservoir stimulation experiment run in 2000 at the soultz sous forets france hot dry rock site that we have interpreted as deep electrokinetic processes using data from another experiment run in 2003 at the same site we show here that the electrically conducting steel casing makes possible the measurement of surface sp anomalies even 5 km above the injection zone but obliterates any information about the geometry of the electrokinetic sources we also observed a slow temporal sp decay after the end of the that we interpret as large fluid flow persisting long after shut in at the edge of the stimulated area this persisting deep fluid flow explains why large induced microseismic events are recorded in this area long after the end of the stimulation experiment as fluid overpressures diffuse far away from the injection area this interpretation is consistent with the diffusive pattern of seismicity analysis of shapiro et al

rock mass behaviour prior to failure abstract changes in stress around mining excavations can result in changes in the behaviour of the rock mass which in turn may lead to damage failure and consequent collapse of the rock mass analysis of documented case studies of regional scale collapses indicates that each rock mass failure is preceded by a precursory manifestation of rock mass behaviour structural damage and progressive failure are manifested by the presence of geotechnical warning signs indicators and precursors and can be exacerbated by triggers indicators suggest that the rock mass may be prone to damage whereas geotechnical precursors demonstrate that the rock mass has been disturbed possibly preceding failure geotechnical analysis of large scale rock mass behaviour also indicates that the failures do not happen at random and are not unpredictable in terms of the type of failure and its location indicators and precursors have to be interpreted in conjunction with mine design mining activities and potential triggers geotechnical monitoring of the precursory behaviour of the rock mass provides timely warning and allows for implementation of remedial measures in this paper these issues are discussed and illustrated in the context of geotechnical risk management

study on electrical potential inversion imaging of abnormal stress in mining coal seam during the mining activities coal rock dynamic disasters have caused grievous casualties and massive property losses it is the severe problem for regional monitoring of abnormal stress electrical potential ep can be produced on coal rock under loading and its response is related closely with the loading stress and damage evolution meanwhile electric field inversion has the advantage to realize regionalization monitoring in the space to identify the abnormal stress localization characteristics in mining coal seam after theoretical derivation the strategy of ep inversion imaging on is studied under bilateral model further simulation experiment of coal rock under loading is conducted the abnormal probability zones of sample can be identified with ep inversion imaging while it corresponds with severe damage zones with significant crack propagation it can be utilized to reveal the localized characteristics of damage and failure of coal rock spatially finally the results of ep inversion in the mining coal seam indicate that the abnormal probability zones can be considered as stress concentration and dynamic hazard areas its effectiveness is verified by microseismic monitoring and rock burst hazard assessment the study provides a new idea to monitor abnormal stress zone regionally and forecast dynamic disasters in the field

tomography of self potential anomalies of electrochemical nature ore deposits and buried metals like pipelines behave as dipolar electrical geobatteries in which the source is due to 1 variation of the redox potential with depth 2 oxido reduction reactions acting at the ore body groundwater contact and 3 migration of electrons in the ore body itself between the reducing and oxidizing zones this polarization mechanism is responsible for an electrical field at the ground surface the so called self potential anomaly a new quick look tomographic algorithm is developed to locate electrical dipolar sources in the subsurface of the earth from the analysis of these self potential signals we applied this model to the self potential anomaly discussed by stoll et al 1995 in the vicinity of the ktb boreholes drilled during the continental deep drilling project in germany the source of this self potential signal is related to the presence of massive graphite veins associated with steeply inclined fault zones within the gneisses and observed in the ktb boreholes

a combined seismic and geoelectrical monitoring approach for co2 storage using a synthetic field site this paper presents an approach to assess the methods of 2d elastic seismic full waveform inversion fwi and electrical resistivity tomography ert for monitoring storage of co2 in deep saline formations as at a real site the subsurface is not fully known this approach uses a synthetic field site densities and saturations are obtained from a numerical simulation of the injection process and are introduced into geophysical forward models which simulate the geophysical data acquisition from the surface fwi and boreholes ert these synthetic geophysical data are then evaluated with respect to changes in co2 saturation and are compared to the fully known co2 saturation of the numerical process model to verify the geophysical monitoring methods results show that both methods are capable of detecting a thin co2 phase body in about 2 200 m depth for a synthetic site in the north german basin inverted co2 saturations are in good agreement however both methods cannot resolve the co2 phase edges of less than 4 m saturated thickness the maximum error of estimated co2 saturation is 10 for the fwi method and 15 for the ert method if accurate baseline models are available the fwi method sensitivity on the baseline model is tested by a sensitivity analysis demonstrating high sensitivity on bulk density but low sensitivity on fluid densities and porosity ert results are considerably improved using structural information from the fwi as constraint