Wstęp

Występowanie sejsmiczności w rejonach eksploatacji górniczej jest zjawiskiem dobrze znanym i musi być rozpatrywane jako jedno z negatywnych oddziaływań górnictwa na środowisko. Jest też przedmiotem specjalnie zaprojektowanych badań sejsmologicznych, górniczych i geologicznych prowadzonych na świecie już od 100 lat, a w Górnośląskim Zagłębiu Węglowym (GZW) zainicjowanych z końcem lat dwudziestych ubiegłego wieku

Badania nad sejsmicznością w Górnośląskim Zagłębiu Węglowym - ewolucja poglądów na pochodzenie wstrząsów

Dzisiaj wiadomo, że występowanie sejsmiczności indukowanej w obszarze eksploatacji górniczej jest wynikiem naruszenia równowagi w górotworze i przejawem niestabilnego wyzwalania akumulowania w nim energii odkształcenia, przy czym źródła akumulowanej energii mogą być różne — zwykle są to naprężenia eksploatacyjne, które mogą się nakładać na naprężenia tektoniczne, lub obserwujemy je w górotworze o właściwościach zdeterminowanych budową i historią geologiczną obszaru. Z naukowego punktu widzenia bardzo istotne jest wyróżnienie naprężeń eksploatacyjnych i ewentualnej składowej tektonicznej, jednakże już R. TEISSEYRE (1983) stwierdził, że „rozróżnianie wstrząsów na eksploatacyjne i tektoniczne może być trudne i bezprzedmiotowe, jeśli powiązanie naturalnej tektoniki i długotrwałej eksploatacji doprowadziło do pola naprężeń, które ze względu na swój charakter i zasięg trudno rozdzielić na części różne przyczynowo”. Z tego też względu tylko długotrwałe badania i obserwacje oraz monitoring obszaru mogą doprowadzić do pewnych korelacji, z których można wyciągnąć odpowiednie wnioski

Podsumowanie wyników i wnioski

Badania zmienności warunków deformacji na podstawie analizy parametrów geometrii uskoków w rejonie siodła głównego pozwoliły określić kryteria regionalnego podziału i wydzielenia obszarów, w których uskoki wykazują zachowanie podobne do podatnego oraz kruchego w okresie deformacji górotworu. Małą podatnością charakteryzują się obszary zlokalizowane w południowym skrzydle uskoku kłodnickiego. W rejonie siodła głównego występują naprzemiennie obszary o średniej i dużej podatności. W obszarach o małej podatności można spodziewać się dużej liczby wstrząsów niskoenergetycznych. W obszarach o wyższej podatności należy się spodziewać wstrząsów o wyższych energiach sejsmicznych. Wdrożenie do praktyki tej analizy pozwoli na zwiększenie dokładności prognozowania sejsmicznego w Górnośląskim Zagłębiu Węglowym

Case Studies of Seismic Energy Release Ahead of Underground Coal Mining Before Strong Tremors

We would like to test the concept that induced seismicity prior to relatively large mining tremor (ML[2.5, E[106J) can be inferred from the cumulative Benioff strain release (BSR) as power law time-to-failure before the strong event. This study presents the application of accelerating BSR prior to a large earthquake, widely used in natural seismicity, for analysis of this phenomenon in induced seismicity. The Benioff strain release is quantified as accelerated releases of cumulative (square root sum) of seismic energy in the time series. During the study, five sequences were extracted from the seismic catalogues from two Polish hard coal mines: exhausted Bobrek Mine (data form the ISEPOS Platform) and from a mine belonging to the Polish Mining Group. Next, a search radius was used to select precursory events and to indicate the type of processes occurring in the coal seam and its vicinity. The fitted power law of cumulative Benioff strain release showed changes of m-parameter. If the value of m was lower than 1.0, the process was regarded as an accelerating-like and if m was higher than 1.0—as a quiescence-like. The investigation of m-parameter vs. the search radius showed the general behaviour of the rock mass in the studied areas and allowed to evaluate the relationship between the critical radius and magnitude of the target event. The obtained scaling relation log(Rc) * 0.35 ML is similar to these reported by other authors who analysed natural seismicity which might suggest that the scaling relation works in a wide range of magnitudes

Determination of Destress Blasting Effectiveness Using Seismic Source Parameters

Underground mining of coal seams in the Upper Silesian Coal Basin is currently performed under difficult geological and mining conditions. The mining depth, dislocations (faults and folds) and mining remnants are responsible for rockburst hazard in the highest degree. This hazard can be minimized by using active rockburst prevention, where destress blastings play an important role. Destress blastings in coal seams aim to destress the local stress concentrations. These blastings are usually performed from the longwall face to decrease the stress level ahead of the longwall. An accurate estimation of active rockburst prevention effectiveness is important during mining under disadvantageous geological and mining conditions, which affect the risk of rockburst. Seismic source parameters characterize the focus of tremor, which may be useful in estimating the destress blasting effects. Investigated destress blastings were performed in coal seam no. 507 during its longwall mining in one of the coal mines in the Upper Silesian Coal Basin under difficult geological and mining conditions. The seismic source parameters of the provoked tremors were calculated. The presented preliminary investigations enable a rapid estimation of the destress blasting effectiveness using seismic source parameters, but further analysis in other geological and mining conditions with other blasting parameters is required

Tectonophysical approach to the description of mining induced seismicity in the Upper Silesia

Seismicity occurring in the Upper Silesian Coal Basin (the USCB) Is induced by deep underground coal mining and is relatively well recorded and recognized. The majority of tremors occurring there, is closely related to mining so only mining induced stresses were considered to be the cause of the tremors. The frequency energy distribution of mine tremors in the USCB has indicated the evident bimodal features: the lower energy mode, closely related to mining and the largest energy indicating the relation to the geological structures of the USCB. Therefore the research has been undertaken to explain if there is any tectonic influence on mine tremors occurrence and to formulate a seismotectonic model of state of deformation and stresses in the rock mass of the USCB responsible together with mining activity for the mine tremors generation. The obtained results indicate that tectonics plays a significant role in the occurrence of at least some of the largest mining tremors in the USCB area and the tectonophysical analysis can explain some relations in their occurrence. On the basis of seismotectonic model constructed for the USCB area we can conclude that the parameters of strain ellipsoid as well as of the seismic moment tensor and regional stress tensor for some mine tremors are almost the same. Some parts of the Upper Silesian Coal Basin (e.g. the zones of large latitudinal faults) are related to the large discontinuities in the deep crustal basement with active shear stresses. The equilibrium disturbance due to the reduction of vertical stress component caused by mining, erosion of the Carpathian overlap or the postglacial rebound may result in unstable behaviour in these zones and one can expect recent horizontal and vertical movements there. We also underline that the application of the optimum method of direct stress (strain) measurement it the rock mass for conditions of the USCB is necessary as well as that the modernization of seismological networks existing there is inevitable

Recognition of the loess covers by using a resistivity imaging method

A main aim of research work was to recognize loess covers by geoelectrical method for three tipped areas, to define loess thickness and show their variability. Resistivity imaging method was used. To research chose Kańczuga Plateau, Nałęczów Plateau and Prydniestrov’ja region (Ukraine). There were used resistivity imaging methods, and the work results were corelated with geological documentation of the research area. The research showed variability in loess covers related to their stratigraphy and allow determine thickness loesses deposit

Wyznaczenie parametrów sprężystych płytkiego ośrodka geologicznego nad wykształcającą się niecką obniżeniową

Seismic and geodetic studies were carried out before, during, and after underground exploitation of a coal bed in Katowice – Kleofas Coal Mine, located in the Upper Silesia Coal Basin, Poland. Development of a subsidence trough was completed approximately 3 months after passage of a longwall exploitation in the coal seam. This was the time required for the subsidence trough to appear on the surface, which was confirmed by levelling measurements. Sharp changes in the elastic parameters were observed on each profile during subsidence trough development. This observation can result from changing tension and compression forces caused by increase and/or decrease of the elastic parameters of the rock mass. After completion of subsidence trough development, the rock mass appeared to return to its isotropic state and the observed changes ceased. Some minor fluctuations were noted, but they probably resulted from changes in groundwater levels, which might have affected the measured parameters

An inversion of rayleigh waves dispersion curves as a tool to recognize the bedrock depth in Chorzów Stary, Poland

Identification of a bedrock beneath soft cover is one of the most important task in engineering geology. The location of boundary-overburden information may be used by investors, builders and municipal authorities to design an infrastructure or land-use plans. In such issues the application of appropriate geophysical methods is useful. However, in urban zones and areas characterized by subsurface soft layer the usage of certain methods (eg.: seismic refraction) is not advisable. The passive method of Refraction Microtremor (ReMi) can fulfill its tasks in the relatively difficult urban environment. The vertical S-wave velocity profiles were carried out as a result of inversion of Rayleigh wave dispersion curves obtained from ReMi method. The change of S-wave velocities allowed to distinguish shallow geological layers in the area of Chorzów Stary. Preliminary measurements allowed to identify the Carboniferous bedrock at a depth of 14 -18 m what has been confirmed by resistivity imaging. Furthermore, unconsolidated deposits are also recognized and the seismic results show a good correlation with the available geological information and resistivity imaging data

Application of seismic parameters for estimation of destress blasting effectiveness

Coal seams in the Upper Silesian Coal Basin are currently extracted under more and more disadvantageous geological and mining conditions. Mining depth, geological dislocations and mining remnants are factors which affect the rockburst hazard during underground mining to the greatest extent. This hazard can be minimized by employment of active rockburst prevention, where long-hole destress blasts in roof rocks (torpedo blasts) have an important role. The main goal of these blastings is to either destress local stress concentrations in rock mass and to fracture the thick layers of strong roof rocks to prevent or minimize the impact of high energy tremors on the excavations. Sometimes, these blastings are performed to make the roof rocks caving behind the longwall face easier. The efficiency of blasting is typically evaluated from the seismic effect, which is calculated based on seismic monitoring data (seismic energy) and the weight of the charged explosive. This method, as used previously in the Czech Republic, was adopted in a selected Polish hard coal mine in the Upper Silesian Coal Basin. This method enables rapid and easy estimation of destress blasting effectiveness, adjusted to conditions occurring in the designed colliery. Destress blasts effectiveness may be evaluated via the seismic source parameters analysis as well, as was carried out in the selected colliery in the Polish part of the Upper Silesian Coal Basin. These parameters provide information, for example, on its size, state of stress and occurrence of slip mechanism in the source of provoked tremors. Long-hole destress blasting effectiveness in selected colliery has been evaluated using the seismic effect method and seismic source parameters analysis. The results were compared with each other and conditions were observed in situ