Mining and Environmental Geophysics. Selected and Revised Contributions to the XXX Polish-Czech-Slovakian Symposium held at Lądek Zdrój on June 6-8, 2005

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Modern approach to the theory and observations of seismic rotation waves is outlined. The spectacular development of the mechanics of continua, including defects, granular structure and other deviations from ideal linear elasticity, was followed by new technical achievements making it possible to detect the rotation waves with the help of very sensitive instruments. The ring laser and fiber coil interferometers concur with the systems of high precision seismographs, including those with the anti-parallel positions permitting to eliminate the displacement velocity motions.

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A pair of earthquakes or seismic events of the same magnitude which occur close to each other during short time interval is called a seismic doublet. These events therefore should not be random. We accepted the following criteria for selection of doublets in the Polish copper mines: the difference in magnitude (based on seismic moment) of two events not larger than 0.15, the distance between their hypocenters not greater than 200 m, and the time interval between their occurrence not greater than 20 days. We considered seismic events from the Polkowice mine that occurred from 1994 to 1996 and from the Rudna mine that occurred between 1994 and 2003 studied previously; their source parameters and focal mechanisms were known, as well as their source time functions in some cases. Altogether, we found in the two mines about 100 doublets and several triplets and quadruplets. Spatial distribution of doublets in particular sections of mines display linear dominant trends, characteristic for a given area, which are often in conformity with the direction of nodal planes determined by focal mechanism of one or both events forming a doublet and with the direction of rupture propagation in their source. Such correlations imply a common origin of seismic doublets associated with dominant fault systems and discontinuities in mines.

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The paper presents a study on energy distribution of seismic events from the Wesoła coalmine (Mysłowice, Poland). The seismic catalogue comprising 14,514 tremors occurring between January 2000 and March 2004 was analysed. Empirical cumulative distribution functions of energy (CDF) were calculated and estimated using Gumbel’s asymptotic distributions. It was stated that the experimental CDFs of low energy events can be estimated by Gumbel’s theoretical distributions of type II.

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About 70 000 mining tremors recorded from 1989 to 2004 at the Jas-Mos coal mine have been analysed. The tremors had seismic energy in the range from 1·103 J to above 1·106 J. 
   Statistical analysis of the concordance of empirical frequency of tremor occurrence distributions with Poisson distribution has been carried out, gradually decreasing the seismic energy discrimination level. Then the distributions of interevent time intervals have been determined verifying if they approached the exponential distribution. 
   It is concluded that in all cases one might determine the energy discrimination levels above which the tremor occurrence approaches the Poisson process. This means that the occurrence of tremors is random, and the consequences concerning their prediction are briefly discussed.

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Focal mechanisms of 168 mining induced seismic events that occurred in the Halemba coal mine area (Upper Silesian Coal Basin, Poland) were determined using the seismic moment inversion method. 38 seismic events were studied in detail. For 12 tremors, non-double couple components were dominant in seismic moment tensor. Focal mechanisms of 38 tremors were repeatedly recalculated for gradually changing vertical Z coordinate values to obtain the maximum double couple seismic moment tensor component. The high value of nonshearing components in seismic moment tensor is probably a result of inaccurrate localization. The non-double couple mining induced seismic events are not so common in the USCB as previous studies suggested.

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A new, approximate but formal predictor of rockburst probability has been presented. Given the predicted values of the mean and variance of the total (AE + tremors) energy that will be emitted from a well-defined time (t,t+Δt) and space (S) region – which are obtainable with the known linear prediction algorithm – it allows to predict the rockburst probability in the same (time and space) region. The region S has to be observed with the seismic and seismoacoustic sensors, cumulated (AE + tremors) energies during the consecutive Δt periods have to be estimated, and the time series of Ec(t) = EAE(t) + Etrem(t) then formed allow the prediction of Ec(t+1) mean and variance. With these values calculated, simple integration (eq. 4.2) allows us to predict the total probability of rockburst. The quality of prediction depends mainly on the quality of the AE and tremors observation.

Abstract:

The cumulative distribution function (cdf) of the magnitude or energy of seismic events is one of the most important probabilistic characteristics in the Probabilistic Seismic Hazard Analysis. The probability distribution function (pdf) of the seismic events magnitude can be estimated through the parametric approach where the magnitude distribution model comes from the Gutenberg–Richter relation or the nonparametric approach using the kernel density estimators. In the nonparametric case, the pdf of the magnitude density estimator is unknown so the confidence intervals of the magnitude cdf are unable to be calculated using the classical methods of mathematical statistics. The evaluation of the magnitude cdf amounts to the point estimate. The same concerns the seismic hazard parameters.
   To assess and reduce errors in the seismic events magnitude or energy estimation, and thereby in the seismic hazard parameters evaluation in nonparametric approach, we propose using resampling methods: the bootstrap and jackknife. These two resampling techniques applied to a one data set provide many replicas of this sample, which preserve its probabilistic properties.
   In this paper we present an example of the use of the developed nonparametric interval estimation algorithm based on the bias corrected and accelerated method (BCa method), with iterated and smooth bootstrap for characterizing the seismicity from an underground copper mine in the Legnica–Głogów Copper District in Poland.

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Analysis of rotational components of the seismic field is a new method in research of the processes in a seismic source. This work presents exemplary results obtained by the differential seismologic method. The chosen seismic events, mainly of mining origin, were registered at the observatories in Książ and Ojców. Two-fold analysis was performed: (i) after filtration of the original data with the pass-band of 0.3-3 Hz, and (ii) after filtration of the same data with the pass-band of 2.6-43 Hz; the obtained pictures of the shocks differ.
   An attempt was made to find what fraction of the seismic energy of a shock was emitted as rotational waves. Various indexes, those known from previous works and also the new ones, were used. The index which informs on the share, in registered seismograms, of the differential components (connected with the rotational ones), was calculated, both for the whole shock and for consecutive short time-intervals; usually it varies in a characteristic way. With the same method, chosen parts of seismograms, bearing apparently only noise, were analysed too. The results obtained in this study had common features with those obtained while analysing seismic events in the Central Appennines and the Pasterze glacier, Austrian High Alps.

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This paper ilustrates advantages of the Bayesian approach to seismic tomography imaging enhanced by the Monte Carlo sampling technique. The theoretical considerations are illustrated by an analysis of seismic data from Rudna (Poland) copper mine. Contrary to the classical LSQR techniques, the Bayesian approach allows to construct not only the “best fitting” model of the sought velocity distribution but also other estimators like, for example, the average model which is often expected to be a more robust estimator than the maximum likelihood solution. We demonstrate that using the Markov Chain Monte Carlo sampling technique within the Bayesian approach opens a possibility of an analysis of tomography imaging uncertainties with a minimal additional computational effort compared to the robust optimization approach.

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The seismicity of California (ANCC catalogue) was tested for the possible tidal and/or non-tidal frequencies. The local maxima of tidal potential were computed as a comparative base using global elastic tidal model of Earth by Wahr-Dehant-Zschau. The imperfect elasticity of the Earth mantle was used. Tidal cycles were defined by the analysis of quasi-periods of tidal potential maxima with comparable lengths. We found semi-diurnal, diurnal, fortnightly, monthly, semiannual, annual, 4.425-years up to 18.6-years long tidal cycles. Ocean tides were not considered.
   Results of the comparison of tidal cycles and seismicity show that tidal cycles with periods equal or longer than semi-diurnal were found in the catalogue and/or in the sub-catalogues.
   Besides the tidal diurnal cycle, the daily (24:00 hours) period was found. This wave has stronger influence on the seismicity than the tidal diurnal cycle. Its origin is connected probably with temperature cycles on the Earth’s surface. The combination of tidal diurnal cycle and daily (24:00 hours) wave leads to the superimposed wave.
   The 7-days and 3-months long periods were also found in the seismicity. They correspond to the half-size of tidal periods. In this case, maxima of seismicity or other seismic parameters coincide both with maxima and minima of tidal potential.

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Tectonic motion along fault is the basic cause of mining induced tremors. Determining focal mechanism of tremor produced by slip on a fault is ineffective with regard to slip direction until rock volume is identified reliably. An orthogonal projection of fault onto the vertical plane containing strike of the fault surface seems to be the technique which can provide information appropriate to help with answering the question about the focal mechanism. The projection enables three-dimensional geometry of fault to be illustrated by constructing contour displacement diagrams and calculating displacement gradients over fault surface. This paper describes displacement distribution along selected wellidentified faults from the central part of the Upper Silesian Coal Basin. Using contour displacement diagrams we have calculated displacement gradients, drawing attention to the existence of four distinct types of pattern. The different patterns are related to different orientations of principal axes that characterise the fault growth. Examining the gradient data patterns, one can determine direction and sense of actual slip on the fault surface. Information brought by displacement geometry analysis, supplemented with ellipticity study and shear moduli calculation, enables kinematic types of faults to be identified. Strike-slip faults, oblique-slip faults, and dip-slip faults can be recognised by means of the presented method. Similarly, left-handed faults can be distinguished from righthanded ones. The procedure presented enables measurements and observation of faults made by mine surveyors to be directly used in seismological interpretations for identifying fault plane responsible for mine tremor occurrence.

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A brief foredesign and status of development of a system to compute seismic signals (SPS) are presented. The system is designed to work in a clientserver system architecture, controlled by the Unix operating system. Authorized SPS users can access resources of the system server via Internet browsers. The resources include gathered data, a set of numerical procedures, and a collection of presentation functions. Users can graphically program the to-be-accomplished tasks using the available software elements and to write their own data processing procedures. Implemented within the system are, among other things, spectral analysis and digital signal processing, in particular signal differentiating and integrating. The system may serve to process (e.g. filter) individual signals, as well as determine common attributes in a collection of signals and further analyze such collections (e.g. attenuation relations). SPS has been designed as an open and scalable software that will be offered free-of-charge under the GPL licence.

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The geomechanical stability assessment of the cultural monument Jeroným Mine at Čistá near Mariánské Lázně, Czech Republic, deals with the issues of the evaluation of the geomechanical condition of the rock mass and the mine workings. This monument supplements the fund of European mining monuments, especially in the area of tin mining and treatment in the period of the second half of the 16th century by the part of old mine workings and in the period of more than 400 years by a part of abandoned mine workings. 
   Since the year 2001, measurements have been carried out to check the crack development in the mine working (mainly by means of plaster and glass targets – 10 measuring points), development in changes in convergence crosssections of linear and spatial workings (21 measuring points) and fluctuations in the groundwater level (4 locations). Detailed surface geophysical survey was made in the same year by the method of apparent resistivity and radiometric measurement. In the year 2004, together with the reconstruction of the drainage adit, seismological monitoring of seismic load on the mine working was started by means of a station installed directly in the mine working. First results of these measurements are presented in this contribution.

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This paper refers to the present state of historical buildings situated in the Karviná and Ostrava region and also to the problems of these buildings caused first of all by surface vibrations generated by mining-induced seismicity in the Karviná region and by technical seismicity caused by industrial activities and transportation in the Ostrava region. Designing of earthquake-resistant structures and analyses of structures affected by surface vibrations are governed by standards ČSN 73 0036 Seismic loads of buildings, ČSN EN 1998–1 Design of structures for earthquake resistance and ČSN 73 0040 Loads of technical structures by technical seismicity. In the second part of this paper, these three standards are described and compared. In the last part of the paper, the measured data from the last six years are shown and reviewed, specifically the maximum values of amplitudes of oscillation velocities. These data come from seismic monitoring using solitary stations of the Institute of Geonics, situated in surface structures in the Karviná region, and from experimental measurements of the influence of transport in Ostrava in 2004.

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Attenuation relations of the transversal and radial components are presented for the absolute acceleration response spectra for 5% damping for 16 periods between 0.05 to 1 s. The equations were obtained using 387 data from three recording stations situated in Polkowice. All models have been tested statistically and for each of them a confidence interval for prediction has been estimated. These relations provide a possibility of predicting the response spectra over the range of epicenter distances less than 2000 m and a source energy logarithm between 5 and 8.

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Two seismic profiles were established for experimental determination of a decrease of the maximum ground motion acceleration amplitudes as a function of the distance and magnitude of seismic sources. Profile I (direction N-S) was equipped by four accelerometers in the period from 2003 July 1 till 2004 December 31. At present, five additional seismometers are dislocated along the Profile II (NW-SE). In this paper, only mining tremors from Legnica-Głogów rockbursts region recorded on Profile I were processed. The local seismic service of Lubin mine yielded data about geographic and time coordinates of foci, as well as local magnitude ML. Magnitude values ML were correlated with magnitude values MV given in the bulletins of near seismic events, recorded by the Czech regional seismic network. Preliminary acceleration attenuation relation was derived for Profile I in the Bohemian massif. Input magnitude ML data are in the interval 2.7-4.1 and epicentre distances are 100-250 km. The obtained relation was compared with two relations derived for data abroad.

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Mining activities in the Karvina region, Czech Republic, provoke seismic events. Some of them may have amplitude values high enough to cause macroseismic effects on the surface. Generalized information about seismic effect on the surface is presented in the form of calculation of contours of maximum values of vibrations velocity for a given event. Measured values from permanent surface seismic stations are input parameters. A small number of these stations and generalized geological pattern of area under study result in local variances between the computed values and values measured using solitaire temporary stations. Therefore, main parameters influencing vibration on the surface are looked for.
   Results of registration in the years 2003-2004 and experimental measurements are presented in this contribution. High differences in the thickness of sedimentary layers of both the Quaternary and Tertiary ages in a small region make it impossible to derive common relations or to use results from other areas.

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The main geological element influencing the temperature changeability within the Halemba Mine area is Kłodnica fault, which divides this area into two parts with different rock temperatures. The area lies to the north of the fault (the upthrow) and is characterized by a higher temperature than in the area located to the south (the downthrow). The same trend is shown in the case of geothermal gradient and geothermal heat flow. The reason for the higher rock temperatures in the upthrow of the Kłodnica fault might be the occurrence of many smaller accompanying faults which could cause the better transport of radiogenic heat from the deeper parts of the rock mass towards the surface and in consequence make the rock temperature higher in the area of Halemba I. The rock temperature rises in the north-east direction. The distribution of temperature in the area of the Halemba Mine is an element of a regional trend, not only the local changeability.

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Katowice Coal Holding which groups 9 collieries is a large producer of high quality steam coal. Mines are generally affected by rockbursts, methane and fires. The paper presents the impact of rockburst hazard on methane hazard and gas emissions. The magnitude of the seismic events and their location are also discussed. The relationship between the above-mentioned hazards for strong events is proved. In the next step, the paper attempts to find a relationship between weak seismic activity and mine gas emissions. Typical exploitation tremors with energy of the order of 10³ J, which were localized in the direct vicinity of the longwall face, were used for the analysis. Apart from CH4 and CO measurements, the air flow velocity in the area was also analysed. Only for several per cent of cases, an increase of CH4 emissions was registered after the occurrence of seismic phenomena. These phenomena had no impact on CO emissions and air flow velocity. A big group of unexplained phenomena was observed (30 per cent of cases), where the occurrence of tremors was preceded by distinct drops of air velocity in the area.

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In the present research, a relationship between seismic wave velocity anisotropy and the distribution of crack orientation parameters was studied using interpretation methods based on tensor calculus. Objects of the research were basalt deposit located within the Sudetian Monocline and diabase deposit located within the Carpathian Foothill. The relationship between velocity and azimuth of seismic profile was established. It was found that the average strike azimuth of separated vertical crack systems determined by direct fracture measurements agreed with the direction of maximum velocity. Results of the present research were compared with the results of earlier measurements carried out in limestone and sandstone deposits located within the Polish Carpathians.
   The existence of relationships between seismic wave velocity anisotropy and fracture parameters makes it possible to use seismic methods for determining the fracture density and the orientation of fracture systems.

Abstract:

The structural research was done in the Silesian-Kraków Upland in two open-cuts of building stone: Dębnik (limestone) and Imielin (dolomite). As a result of the investigations, the directions of fracture systems were delineated and block divisibility was calculated, as principal parameters in the documentation of building stone.
   Simultaneously, geophysical methods were applied using shallow seismic refraction. According to the azimuthal velocity of wave propagation, the orientation of fracture was estimated. In Dębnik a strong anisotropy of seismic waves occured and there was an excellent correlation between structural and seismic measurements, whereas in Imielin this correlation was rather weak, which was probably caused by using explosives for mining in the open-cut. The calculation of block divisibility using a seismic method was not possible in this case.

Abstract:

The application of the shallow refraction seismic method for analysis of block divisibility of natural building stone is presented for an example of the Górka-Mucharz sandstone deposit (Polish Carpathians). Geological block divisibility is a relative participation of the block material in a deposit, profile etc. The applied method reflects the main fracture directions to the satisfactory degree but the estimation of fracture linear density has only an approximate character. The authors suggest the possibility to set the volume of average block as an additional (geophysical) index of the block divisibility.

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This paper contains the results of preliminary study of landslides located in the Polish Flysch Carpathians. The resistivity imaging method in connection with direct geological and geodetic methods was applied to investigate five small landslides situated in Nowy Sącz. The goal of this work was to test the resistivity imaging method for identifying the geological structure of landslide, especially the weathered cover of the flysch. Marking out the slip plane was also an object of interest. Measurements were carried out during the long period of drought which resulted in significant decrease of ground water table. Very dry rock mass and horizontal variability of the landslide structure caused considerable difficulty in the explicit interpretation of the geoelectrical tests.

Abstract:

Abandoned shafts, even if backfilled, create a potential hazard for the environment and safe use of post-mining lands. The hazardous phenomena depend on the shaft tube structure and the extent of mining activity in the vicinity and, on the other hand, the dynamic processes which occur within rock strata. Among the processes which affect the rock mass structure is the rainfall water migration and erosion. The amount and rate of water flow within soil and bedrock in the specific area depend on time. The water saturation in rock formation is the main factor which determines the electric properties of geological environment. These phenomena can be used for monitoring erosion processes by electroresistivity or conductometric measurements. In the paper, experimental results of the tests carried out in an abandoned shaft site are described. The tests were performed in three series of measurements conducted using vertical electroresistivity sounding method (VES) in autumn, winter and spring. The results indicate significant changes of rock formation resistivity values due to change in seasonal conditions. This impacts the interpretation of the data collected in geoelectrical measurements.

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The article shows the results of an application of geoelectrical methods for identifying places of pollution and contamination in the area of former military fuel base located 2 km west of Borne Sulinowo.

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Sinkholes are natural phenomena in the landscape that cover the majority of old mining sites of shallow hard coal and zinc-lead exploitation in the Silesian Coal Basin and in the Olkusz area. Each sinkhole has unique characteristics due to the mechanism of its occurrence. Some of them are related to old, abandoned shafts, often not quite well closed. 
   Dependence of sinkhole diameter upon overburden soil parameters has been established by numerical modelling. This dependence correlates quite well with the hypothesis of Professor Chudek, which has not been proved yet.
   The paper discusses some theoretical aspects of sinkhole occurrence in the conditions of the Silesian Coal Basin. In the core part, basic assumptions and results of numerical calculations are presented. Finally, the calculated dependence and the resultant graphs are compared to the analytical ones.

Abstract:

The aim of the paper is to present preliminary results of studies of natural radioactivity of selected rocks from the Vysočina region occurring relatively close to the Rožná (Czech Republic) uranium deposit. Measurements allowed to determine the activity concentrations of 40K and nuclides from 238U and 232Th series in investigated rocks and compare the noted activities with average activity concentrations of these radionuclides in the continental crust and soil. Appearance of regional natural radioactivity anomaly could be determined on the basis of the obtained results.

Abstract:

Sedimentary rocks from the borders of Krzeszowice graben have been the most popular origin of building materials in the whole Kraków region since the Middle Ages to the present day. Apart from using these rocks for building purposes, they are also used in road construction industry and as a part of sorbent for desulphurisation of combustion gases. It is vital to know the background radiation of these rocks. In situ gamma ray spectrometry was used to determine the activity concentrations of nuclides from U series, Th series and potassium 40K in selected rocks that were mostly of the Paleozoic age.

Abstract:

This paper presents the results of a non-invasive geophysical investigation of an archeological position in Cieszacin Wielki. The study was carried out on a group of ancient ground mounds. The main aim of the present investigation was to recognize the internal structure of one of the selected mounds and delineate the anomalies of the zones which might be related to archaeological objects in the cover of the mound. Three geophysical methods were used: magnetic, electromagnetic and resistivity imaging. The results are presented on the maps of magnetic anomalies ΔT, maps of apparent ground conductivity and shallow resistivity inversion up to 2 m in depth.
   The results were combined with the geological cross-section and geochemical data obtained from the environs of the mound.