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1
Content available Passive Seismic Tomography at Rudna Copper Ore Mine
EN
Seismic tomography is a technique widely used to image the Earth’s interior at various scales, from the very local subsurface to the whole Earth’s interior. Successful tomographic applications in seismology have opened the question of whether, or not, the method can also be helpful in assessing the safety of mining operations. Long-time efforts and accumulated evidence with tomography imaging carried out at the Rudna copper mine clearly indicate that this is really the case. Repeating imaging of velocity distributions reveals that the observed temporal changes provide information that is useful for improving the safety of mining processes. In this paper, we describe our experience of performing seismic passive velocity tomography at the Rudna copper ore mine in the south-western part of Poland. We consider only the last 10 years, when the geophysical unit of Rudna copper mine began using an advanced modern tomography software developed originally for this mine.
EN
A better understanding of rockburst precursors and high stress distribution characteristics can allow for higher extraction efficiency with reduced safety concerns. Taking the rockburst that occurred on 30 January 2015 in the Sanhejian Coal Mine, Jiangsu Province, China, as an example, the mechanism of rockburst development in a roadway was analysed, and a combined method involving b values and seismic velocity tomography was used to assess the rockburst in both time and space, respectively. The results indicate that before the rockburst, b values dropped significantly from 0.829 to 0.373. Moreover, a good agreement between a significant decrease in b values and the increase of the number of strong tremors was found. Using seismic tomography, two rockburst risk areas were determined where the maximum velocity, maximum velocity anomaly and maximum velocity gradient anomaly were 6 km/s, 0.14 and 0.13, respectively. The high-velocity regions corresponded well with the rockburst zone and large seismic event distributions. The combination of b values and seismic tomography is proven to have been a promising tool for use in evaluating rockburst risk during underground coal mining.
PL
Badania miały na celu rozpoznanie właściwości górotworu w aspekcie występowania anomalii sejsmicznych, mających związek ze zjawiskami gazogeodynamicznymi w rejonie pola XXVIII/1 w ZG „Rudna”. Badania były ukierunkowane na rozpoznanie właściwości warstwy dolomitu w stropie wyrobisk górniczych. Zostały one przeprowadzone w rejonach o kilkusetmetrowych wymiarach, z wykorzystaniem 96 czujników, specjalnie rozmieszczonych i zainstalowanych oraz kilkudziesięciu otworów strzałowych, w których odpalano 100-300 g ładunek MW. W wyniku badań obliczono i opracowano mapy izolinii zmian parametrów sejsmicznych. Posłużyły one do sformułowania wniosków odnośnie do zmian właściwości górotworu oraz do zaprojektowania i wykonania otworów kontrolnych. Wyniki badań można również wykorzystać przy prowadzeniu robót przygotowawczych i eksploatacyj-nych w polu XXVIII/1.
EN
The study aimed to identify the properties of the rock mass in terms of seismic anomalies relevant to the recognition of gaso-geodynamic threat zones in the area of XXVIII/1 field in the Rudna copper ore mine. The research was carried out in dolomite layer in the roof of the mine workings. This was done in areas with several hundreds meters dimension, using 96 geophones, especially arranged and installed, and several tens of blast holes, which were fired 100-300 grams of explosives. In the result, maps of seismic parameters' changes were calculated and performed. These were used to formulate conclusions about changes in the properties of the rock mass and for the design and construction of control boreholes. The test results can also be used to carry out preparatory and exploitation works in the XVIII/1 field in Rudna copper ore mine.
PL
W artykule przedstawiono wyniki tomografii sejsmicznej wykonanej na wybiegu ściany w pokładzie 510 w jednej z kopalń w Górnośląskim Zagłębiu Węglowym oraz analizę mechanizmu ognisk średnio- i wysokoenergetycznych wstrząsów górotworu, jakie wystąpiły w rejonie tej ściany bezpośrednio po przeprowadzonych badaniach geotomograficznych. Uzyskany rozkład naprężeń w górotworze na wybiegu ściany oraz wyniki przeprowadzonej analizy mechanizmów ognisk wstrząsów skorelowano ze sobą oraz z warunkami górniczo-geologicznymi. Na podstawie przeprowadzonych badań określono czynniki mające dominujący wpływ na kształtowanie się zagrożenia tąpaniami w rejonie eksploatowanej ściany w przyjętym przedziale czasowym. Jednoczesne wykorzystanie tomografii sejsmicznej i analizy mechanizmów ognisk wstrząsów umożliwia pełniejsze rozpoznanie zagrożenia tąpaniowego w trakcie prowadzonej eksploatacji.
EN
The article presents the results of seismic tomography conducted ahead of the longwall front in coal bed 510, in a mine of the Upper Silesian Coal Basin, along with the analysis of medium- and high-energy tremors of the rock mass which occurred in the longwall area directly after the geo-tomographic research. The achieved stress distribution in the rock mass ahead of the longwall front, as well as the results of the tremor source mechanisms were correlated with each other and with the mining and geological conditions. Based on the conducted research, the factors were identified which impact rock-burst hazards in the area of the exploited longwall in the assumed period of time. Simultaneous use of seismic tomography and the analysis of tremor source mechanisms enables better identification of rock-burst hazards during the longwall exploitation.
EN
Controlled-source seismology (CSS) is the primary source of information regarding the fine structure of the lithosphere. The aim of this paper is to provide an overview of the methods that are commonly used to derive Earth models from CSS data with the focus on the wide-angle reflection/refraction method. Some outlook on the future of the CSS is presented with the special emphasis on the full-wavefield based methods like full-waveform inversion, which brings high level of objectivity into modeling, as well as significantly increases spatial resolution. It is stressed that the researchers should be aware of the limitations of how the elastic parameters transcribe into the actual rock properties which should stimulate them to go beyond the simple P-wave modeling and to build multiparameter Earth models based either on the seismic data or constrained by additional geophysical fields in order to derive sound geological interpretation of their models.
EN
Detailed imaging of the Earth subsurface structure has both scientific and practical aspects. From a scientific point of view knowledge of the Earth’s structure is necessary for understanding various processes. Practical aspects include such issues as localization and description of natural resources deposits. Although huge progress has been made in this field, there are still a lot of questions not answered yet. One of them is the question of a relation between observed seismicity and the earth’s structure. In this paper we address this issue and argue that the probabilistic (Bayesian) approach should be used. Since this inversion method introduces some additional complexity to the already difficult seismic tomography technique, we decided to describe the basic steps of Bayesian tomographic imaging from data preparation to analysis of imaging results. The methodological considerations are illustrated by examples of imaging for four mining regions within the Rudna (Poland) copper mine.
EN
First-arrival traveltime tomography was applied to high-resolution seismic data acquired over a known quick-clay landslide scar near the Göta River in southwest Sweden in order to reveal the geometry and physical properties of clay-related normally consolidated sediments. Investigated area proved to be a challenging environment for tomographic imaging because of large P-wave velocity variations, ranging from 500 to 6000 m/s, and relatively steeply-dipping bedrock. Despite these challenges, P-wave velocity models were obtained down to ca. 150 m for two key 2D seismic profiles (each about 500-m long) intersecting over the landslide scar. The models portrait the sandwich-like structure of marine clays and coarse-grained consolidated sediments, but the estimated resolution (20 m) is too small to distinguish thin layers within this structure. Modelled velocity structures match well the results of reflection seismic processing and resistivity tomography available along the same profiles.
8
Content available remote Tomografia sejsmiczna w górnictwie
PL
Prędkościowa tomografia sejsmiczna jest techniką bezinwazyjnego obrazowania budowy wewnętrznej próbek skalnych, masywu skalnego, struktur geologicznych itp. w skalach począwszy od ułamka metra do tysięcy kilometrów. Otrzymywane tą techniką przestrzenne rozkłady prędkości fal P i S są zwykle interpretowane w kontekście strukturalnej budowy badanego górotworu. Jednakże, z punktu widzenia zastosowań w górnictwie jednym z najważniejszych elementów badania tomograficznego jest próba interpretacji otrzymanego obrazu tomograficznego pod kątem stanu naprężeń w górotworze. Osiągnąć to można albo przez próbę korelacji aktywności sejsmicznej z anomaliami rozkładu prędkości albo przez interpretacje anomalii prędkości pod kątem zmiennego w przestrzeni pola naprężeń. Niezależnie od wybranego podejścia dla poprawnej interpretacji tomogramów bardzo ważna jest ocena wiarygodności otrzymanych pól prędkości. Celem niniejszej pracy jest przybliżenie zasad tomografii sejsmicznej oraz wspomnianego powyżej dwoistego podejścia do praktycznej interpretacji wyników badań tomograficznych.
EN
The seismic velocity tomography is a non-destructive technique of imaging of the structure of rock samples, rock mass, geological structures etc. at scales ranging from centimetres up to thousands of metres. The obtained by use of this technique spatial distributions of P and S waves are usually interpreted in the context of the internal structure of the imaged rock mass. However, from the point of view of applications in mining one of the most important elements of tomographic inversion is the attempt of interpretation of the obtained tomographic image in the context of the state of stresses in the rock mass. This can be achieved either by an attempt of correlation of seismic activity with anomalies of the velocity distribution or by the interpretation of velocity anomalies in terms of lithological parameters. Independently of the chosen approach, for correct interpretation of tomograms very important is the assessment of reliability of obtained velocity fields. The aim of the present work is the approximation of seismic tomography rules and mentioned above dual approach to the practical interpretation of tomographic investigation results.
9
EN
Inversion of seismic tomography is non-uniqueness and bad-conditioned problem. Reconstruction of velocity field is a process of minimization error function between estimated and received travel times. Classical, deterministic method, like matrix decomposition or conjugate gradient, is known for finish calculation in local minimums. Other problems with deterministic methods were application of constraints to the solution. Stochastic algorithms are methods that can be helpful in solving inverse problem in seismic tomography. This paper presents application of the following two stochastic algorithms to reconstruct velocity field: Metropolis algorithm (MA) and simulated algorithm (SA). The Metropolis algorithm is an iterative method and it was first described by Metropolis et al. (1953). This method uses Boltzmann distribution to calculate probability of replacing current solution by worse one, which is modification of current. Level of acceptance is given by value of a temperature. The simulated annealing was first described by Kirkpatrick et al. (1983) and it is a modification of Metropolis algorithm. This algorithm decreased temperature during iterative process. Both algorithms were modified by adding two dimensional median filtration in a place of modification of current velocity field. This filtration was applied with some small probability. Estimation of travel times of primary seismic waves was performed using two ray-based methods: a straight line and a shortest path method (Moser 1991, Pięta & Dwornik 2009). The first method was very fast but nonrealistic in heterogeneous geological medium. The second method had over one hundred times longer calculation time, but provided real ray trajectories. The algorithms were tested in series by ten independent numerical simulations for each parameter of configuration to minimize random effects of stochastic methods. Both algorithms were initialized in two ways: by random velocity fields and by velocity field obtained by SIRT algorithm (Lo & Inderwiesen 1994). Application of median filtration and initializing by SIRT solution decreased calculation time and improved quality of inversion.
EN
Consider the problem of reconstruction of a small perturbation of the acoustic wave speed field from traveltime data with linear background slowness. Mathematically, the problem is equivalent to reconstruction of a function from the data of integrals along the circle arcs. The data is limited, in the sense that the base points belong to a compact set. We propose and numerically test a new approach, based on reduction of the problem to the inverse problem for the Radon transform. The data completion procedure is considered as well.
PL
W artykule wymieniono i omówiono kilka przykładów badań geofizycznych (i ich wyników) wykonanych przez Przedsiębiorstwo Badań Geofizycznych Sp. z o.o., dotyczących płytkiej prospekcji ośrodka geologicznego. Przedstawione przykłady odnoszą się do badań, w których wykorzystano najnowsze technologie z dziedziny sejsmiki inżynierskiej i tomografii elektrooporowej. Omówiono podstawowe aspekty praktyczne w odniesieniu do potencjalnych możliwości zastosowania tych metod w geologii inżynierskiej.
EN
The article presents and discusses a few examples of the results of geophysical surveys carried out by the PBG Ltd., for the near surface prospecting of the rock medium. The presented examples refer to studies that use the newest technologies in engineering seismics and electric resistivity tomography. Fundamental practical aspects in relation to potential applications of these methods in engineering geology are discussed.
EN
The Doupovske Hory Volcanic Complex (DHVC) is the bestpreserved large volcanic suite of the Cenozoic intraplate volcanism in the Bohemian Massif. However, many uncertainties remain in the geological setting of its basement. In summer 2008, two seismic refraction profiles ran across this area to reveal the depth of the volcanic rocks and the underlying geological structure. A high-velocity body was detected beneath the central part of the DHVC at depths of about -500 m a.s.l., inclined to the NW at an angle of about 45°. This body is most likely formed by the basic and ultrabasic rocks (amphibolites, eclogites, serpentinites, metagabbros) of the Equivalent of the Marianske Lazne Complex (EMLC). Subvolcanic rocks of the DIC penetrating these basic and ultrabasic metamorphic rocks have very similar physical properties. Therefore, intrusive body of the Doupov Intrusive Complex (DIC) can be hardly distinguished from rocks of the EMLC by seismic refraction investigation.
EN
Salt Dome “Góra” was studied with seismic tomography method. Three profiles are described. The interpretation of wave pictures helped to locate the walls of the studied salt dome’s. The research confirmed the salt dome has good properties for storage of gas or toxic and radioactive wastes.
EN
Carpathians geology is very complex and seismic horizons are highly deformed by tectonic movements, existence of thrusts, numerous faults and fracture zones. Therefore, the geological interpretation beneath the overthrust is uncertain and wells cannot be reliably located. Under complex geological conditions, time migration algorithms generate errors resulting from strong horizontal velocity changes. Moreover, the proper focusing of dissipated energy requires application of a PreStack Depth Migration (PreSDM). Proper depth imaging depends on appropriateness of velocity model used for PreSDM. Unfortunately the complexity of velocity changes limits the effectiveness of conventional velocity analysis techniques. The article focuses on PreSDM velocity model building process for data acquired in complex overthrust environment. The method is based on dual usage of tomographic inversion together with combination of non-seismic information. Combination of tomographic results with well velocities increases convergence of the method. It also limits an ambiguity and improves reliability of final velocity model. To justify the proposed method, the border value of possible tomographic velocity updates was evaluated. The method was tested on two different datasets acquired in the Polish Carpathians.
EN
Standard seismic tomography is based on the first arrival refracted Pg- and Pn-waves travel times and as a result gives a smooth model of the structure. Sharp discontinuities, particularly the Moho, as well as lower crust, are poorly constraint. The paper presents a modification of the standard method which allows to use later arrivals of crustal Pcr waves together with the first arrival travel times. They give better coverage by rays and better model for the whole crust. Results are illustrated by synthetic models and interpretation of experimental data from POLONAISE'97 profile P4.
16
Content available remote Mantle plumes and dynamics of the Earth interior : towards a new model
EN
Seismic tomography provides reconstructions of thermal-density structure of the Earth's mantle as deep as the mantle/core boundary (CMB). For the first time, a direct image of dynamic processes, occurring inside the globe, was obtained. Existing plate-tectonic models of modern geodynamics lead to a number of discrepancies. Most important are: stationary position of mantle plumes as the assumption of the convection process in the Earth's mantle, mantle convection versus data on both its viscosity and the existence of global seismic discontinuities, possibility of horizontal displacements of lithospheric plates above the discontinuous LVZ zone which disappears under deep-seated continental "roots", the model of radially growing distance between mid-oceanic ridges and Africa (also Antarctica), the growing separation between hot spots occur in neighbouring plates with time, geophysical data indicative of considerable input of energy and material from the Earth's core into the mantle, uncompensated by any exchange between the lower and upper mantle. New models (multi-layered convection or a plate-tectonic hybrid convection model) intend to explain tomographic image with taking into consideration geochemical data but with miserable results. The nature of mantle convection still remains controversial. The phenomenon of stationarity of hot spots relative to the accepted plate movements and the absence of evidence indicating deformations of mantle plumes by the convection system are also unclear and controversial. The presented model of the expanding Earth's offers a reasonable solution to these discrepancies and paradoxes.
PL
Obserwacja propagacji energii sprężystej w masywie skalnym zapewnia wiarygodną informację na temat stanu naruszenia masywu. W aspekcie oceny operacyjnej naruszenia masywu skalnego wskutek użycia materiałów wybuchowych występuje potrzeba rozwinięcia dynamicznych metod impulsowych. Zastosowanie technik komputerowych do obróbki sygnału sejsmicznego umożliwia rozwinięcie impulsowych metod dynamicznych w odniesieniu do badań masywu skalnego dla celów oceny geotechnicznej. Jedną z takich metod jest tomografia komputerowa z wykorzystaniem danych pomiarowych. Jednym z podstawowych składników takiej tomografii jest analiza przestrzenna, stosowana do przedstawiania i wizualizacji położenia miejsc nieciągłości, przydatna w planowaniu przedsięwzięć przemysłowych i naukowych. W artykule przedstawiono pomiary laboratoryjne i analizę przestrzenną pomierzonych danych dla przypadku lokalizacji nieciągłości i tworzenia przestrzennego modelu masywu skalnego.
EN
Observation of elastic energy propagation in rock massif provides credible information of complex rock massif violating. In aspect of operative judging of massif violating by using explosive, is necessary advancement for creation in using impulse dynamic method. Application of computer technologies to seismic signal operation is a viable way of increment a possibilities of impulse dynamic methods in rock massif for geotechnical judging. One of usable way is a computer tomography using for measured data manipulation. One of elemental component of computer tomography is a spatial analysis, which is used to presentation and visualization of current location of discontinuities in case of planned industrial and scientific activities. In this paper laboratory measurements and spatial analysis of measured data are presented in case of discontinuities location and rock massif spatial model creation.
EN
Initial evaluation has been undertaken for improving tomographic images in vertical seismic profiling (VSP) by utilization, in addition to direct wave, the reflected wave as well. This evaluation has been performed basing on model computations. The input data in tomographic inversion have been traveltimes generated using ray tracing with curved rays for selected seismogeological medium models. It was proved that when we use traveltimes of wave reflected from the reflector in the bottom of transmission medium we can considerably improve the range of medium coverage with seismic rays and create a possibility to define much more precisely the location of velocity heterogeneities during tomographic inversion.
EN
Aftershocks which followed the 1995 Egion earthquake of magnitude ML=6.2 were used to detrminea preliminary P-wave velocity structure of the upper crust in a region of the western part of the Gulf of Corinth, western Greece. 680 selected P-wave arrival times from 108 aftershocks recorded by the seismic network PATENT of the University of Patras and the temporary EGION network were inverted for the P-wave velocity distribution with respect to two classes of models: horizontal homogenous layers and a single laterly heterogeneous half a space. Travel time data were inverted both in a standard way using the damped least-square approach and using Cauchyrobust norm and genetic algorithm optimization method in the framework of the Bayesian inversion scheme. Although the main features of P-wave distribution obtained by both approaches are similar, the differences were found to be up to a few percents even in a well resolved area. Generally, the models obtained by genetic algorithm provide smaller residua then those calculated by means of the damped least-squares. It has also been found that the main shock of 15 June and most of considered aftershocks occurred in the region of an increased velocity (about 0.4km/s) as compared to the average velocity of an adjacent area.
PL
W poniższym artykule przedstawiono zastosowanie metody tomografii sejsmicznej do badania niejednorodności oraz monitorowania zmian, jakie zachodzą w wyniku wzmacniania stwierdzonych w badanej przestrzeni stref anomalnych (osłabionych). Prezentowane wyniki uzyskane zostały z prześwietlań korpusu zapory betonowej w Wapiennicy, które realizowano w wybranym bloku korpusu przed i po pracach remontowych. Omówiono zastosowanie tomografii prędkościowej i tomografii tłumienia w monitorowaniu efektywności prac remontowych oraz porównano rezultaty uzyskiwane dla obu odmian metody.
EN
Possibility of use of seismic velocity and attenuation tomography measurements to diagnosis of anomaly zones of concrete dams has been discussed in this paper. Some examples of the correlation and differences between velocity and attenuation tomography are presented. Results of tomography measurements, obtained for the concrete dam in Wapiennica, are shown in form of distribution maps of the P-wave velocity and attenuation coefficients. Repetition of tomographic measurements in the same geometry can supply useful information on changes of the integrity of concrete dams.
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