SEISMIC LOAD OF STRUCTURES IN KARVINÁ REGION DERIVED FROM LONG-TERM MONITORING

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1 GÓRNICTWO I GEOLOGIA 2010 Tom 5 Zeszyt 2 Zdeněk KALÁB, Markéta LEDNICKÁ VSB Technical University, Ostrava SEISMIC LOAD OF STRUCTURES IN KARVINÁ REGION DERIVED FROM LONG-TERM MONITORING Summary. This paper presents results of long-term monitoring of seismic load of structures situated in undermined Karviná region. Data from seismological monitoring were used for seismic load evaluation in terms of new methodology. Main idea is recalculation of maximum measured velocity values to have possibility to take into account number of seismic events and number of intensive seismic events especially. This methodology was elaborated for evaluation of seismic load of given place caused by mining induced seismicity for the purpose of maps of conflicts of interests. Trends of seismic load of structures are documented using changes of C coefficient calculated from data that were obtained on seismic stations situated at the surface in the Karviná region during last ten years. OCENA ZAGROŻENIA SEJSMICZNEGO DLA OBIEKTÓW W REJONIE KARWINY, NA PODSTAWIE WYNIKÓW DŁUGOFALOWEGO MONITORINGU Streszczenie. W ramach pracy przedstawiono wyniki monitoringu sejsmicznego, prowadzonego w rejonie Karwiny w długim okresie czasu. Wyniki pochodzące z monitornigu były wykorzystane do opracowania nowej metodologii oceny skutków aktywności sejsmicznej wywołanej eksploatacją górniczą z uwzględnieniem długofalowych skutków tych oddziaływań. Metodologia ta zakłada przeliczenie maksymalnych prędkości zarejestrowanych fal sejsmicznych z uwzględnieniem liczby wstrząsów, biorąc pod uwagę szczególnie wstrząsy o dużej intensywności. Zaproponowano odpowiednią miarę zagrożenia sejsmicznego w postaci współczynnika C, którego wartości ustala się na podstawie wyników długofalowego monitoringu. Przedstawiony przykład opiera się na danych zarejestrowanych na stacjach sejsmicznych zlokalizowanych na powierzchni w rejonie Karwiny w okresie ostatnich 10 lat. 1. Introduction Special methodology for load evaluation of structures by mining induced seismic events was elaborated within the project named CIDEAS (Centre for Integrated Design of Advanced Structures). Main idea is recalculation of maximum measured velocity values to have possibility to take into account number of seismic events and number of intensive seismic

2 60 Z. Kaláb, M. Lednická events especially. The Karviná region was selected for presentation of the methodology [4] and for presentation of first results using real data from selected seismic stations [8] Karviná area is a region with very intensive seismic activity induced by mining activities [2, 5, 7]. Annually about 40 thousands seismic events are recorded; from 100 to 500 of seismic events have local magnitude higher than 1. Effects of mining induced seismicity can be evaluated according Czech technical standard ČSN Loads of technical structures by technical seismicity by determining of degree of damage of structures. Maximum measured value of oscillation velocity, type of foundation soil (a c) and class of resistance of structures (A F) enter the evaluation of degree of damage (0 5). This evaluation is based on maximum measured value of oscillation velocity, but does not consider long-term and multiple character of load, which is specific for mining induced seismicity. Effects of multiple and long-term seismic load and their impacts on structures are considered using multiple coefficients signed as C in methodology presented below. Study of trend of C coefficient is presented in this paper. Measurement of the oscillation velocity at the surface First solitary seismic stations performed by the Institute of Geonics were established in 1997, but long-term monitoring has started since These surface seismic stations are situated in selected buildings [3]. Position of individual seismic stations has changed during long-term monitoring depending on different reasons. Exploitation in complicated geomechanical conditions and special research tasks were the most frequent reasons. Long-term monitoring was started in the years , when four solitary seismic stations were established within the Program of Research and Development of the Czech Mining Bureau: 1/ in the area of Orlová City (ORL 1 and ORL 2), 2/ Doubrava Village (DOU 1) and 3/ Stonava Village (STO 1). Since 2003, the measurement has been running with the Czech Science Foundation support (Project No. 105/03/0078). Two more stations were established in 2004: in the area of Darkov Village (DAR 1) in 2003 and in the area of Karviná (KAR 1). Next station in Stonava area (STO 2) has been established in the year 2007 within the Czech Science Foundation support (Project No. 105/07/0878). Sketch of seismic stations location is presented in Fig. 1.

3 Seismic load of structures in 61 Fig. 1. Situation of seismic stations in Karviná region operated by Institute of Geonics during 2000 ) Rys. 1. Lokalizacja powierzchniowych stacji sejsmicznych, pracujących w Karwinie w latach 2000, obsługiwanych przez Instytut Geoniki Data from seismic stations mentioned above are recorded in a trigger mode after exceeding the pre-set level of the oscillation velocity. Digital recorders of PCM3-PC and PCM3-EPC types with three-component seismometers are used for these measurements [6]. The seismometers are oriented to geographic directions, the third component is vertical. A review of maximum measured values of spatial component amplitudes of the oscillation velocity at particular stations in 2000 is given in Tab. 1. Table 1 Review of maximum measured values of spatial component amplitudes of the oscillation velocity at particular stations in 2000 with monitored and analysed periods period of monitoring analysed period in this study maximum value of spatial component of oscillation velocity (mm.s -1 ) ORL 1 ORL 2 DOU 1 STO 1 DAR 1 KAR 1 STO

4 62 Z. Kaláb, M. Lednická Selected input data sets from seismic stations ORL 2, STO 1, STO 2, DOU 1, DAR 1 and KAR 1 were used for evaluation of seismic load according methodology described below. It is necessary to use data set without (long-term) data interruption. Therefore, it was not possible to use data from seismic station ORL 1 because of repeated interruptions of data set. Analysed period of data sets from other stations is specified in Tab. 1. All analysed periods include maximum measured value of oscillation velocity. Main idea of our methodology is to recalculate maximum measured value of velocity to total value of velocity in the time period of 12 months. Input data set includes those seismic events that exceed the value of 0.5 mm.s -1 at least on one measured component. Only data sets containing spatial components were used for the purpose of this study. 2. Calculation of total value of velocity Resultant value of the calculation is so called total value of velocity in given point for analyzed period signed as x i. Values x T are results for input data sets containing absolute values of spatial component [4]. Description of calculation can be summarized briefly subsequently. Analysed period T is 12 months. Basic equations are as follows: x T = x max * C N * C M = x max * C x max maximum value of spatial component in given period T C N coefficient that takes into account the number of recorded seismic events in given period T C M coefficient that takes into account the number of recorded intensive seismic events in given period T The coefficients for Karviná region are calculated using equations: C N 1 N 200 arctg( ) C M = C M0 * C M1 * C M2 N total number of recorded seismic events with value of minimally one component higher than 0.5 mm.s -1 in given period T C M0 partial coefficient that takes into account number of recorded seismic events in given period T with maximum value in range 3 6 mm.s -1 C M1 partial coefficient that takes into account number of recorded seismic events in given period T with maximum value in range 6 10 mm.s -1

5 Seismic load of structures in 63 C M2 partial coefficient that takes into account number of recorded seismic events in given period T with maximum value above 10 mm.s -1 The partial coefficients are defined using equations: C M0 = * ln (N 0 ) C M1 = * ln (N 1 ) C M2 = * ln (N 2 ) Numbers in individual data sub-sets are defined: N 0 number of recorded seismic events in given period T with maximum value in range 3 6 mm.s -1 N 1 number of recorded seismic events in given period T with maximum value in range 6 10 mm.s -1 N 2 number of recorded seismic events in given period T with maximum value above 10 mm.s Analysis of long-term trends of seismic load Total value of velocity as a result of the methodology described above is function of multiple coefficients C and maximum measured value of oscillation velocity. The multiple coefficients C determine significance of mining induced seismic load. For the presentation of progress of seismic load in time, calculation was made using moving overlap time window. Length of time window is 12 months; step and length of overlap are 1 month. Period of one time window was signed as epoch and calculated results relate to end of given epoch. For example, total value of velocity and multiple coefficient C for epoch VI-05 describe seismic load during period from July 2004 to June 2005 (see Fig. 2). Resulting graphs on Fig. 3 represent trends of multiple coefficients C for selected seismic stations from Karviná region during the years As is possible derived from graphs on the figure 3, multiple coefficients C do not exceed value 1.1 on seismic stations STO 2, KAR 1, DAR 1 and ORL 2. Two stations reach higher values of multiple coefficients C, i.e. value 1.21 for STO 1 and 1.36 for DOU 1. These higher values of multiple coefficients C are result of extremely high value of measured oscillation velocity and/or high number of seismic events. Coefficient C reflects on higher seismic load at given points. Degree of damage of structures at these places may be higher than degree of damage determined according CSN only by maximum measured value of velocity.

6 64 Z. Kaláb, M. Lednická Fig. 2. Illustration of moving time windows (data from station STO 1 squares) Rys. 2. Ilustracja ruchomego okna czasowego (dane ze stacji STO 1 kwadraty) value of multiple coefficient C 1,4 1,35 1,3 1,25 1,2 1,15 1,1 STO 01 KAR 1 DAR 1 DOU ORL 2 STO 2 1,05 1 VI-00 VI-01 VI-02 VI-03 VI-04 VI-05 VI-06 VI-07 VI-08 VI-09 VI-10 Fig. 3. Trends of multiple coefficients C on selected seismic stations in Karviná region during the years 2000 Rys. 3. Zmienność współczynnika C na podstawie odczytów z wybranych stacji sejsmicznych w rejonie Karwiny w latach 2000 epoch 4. Conclusion New methodology for evaluation of seismic load of structures at the surface is presented. Multiple coefficient C is used for this purpose because it enables to include effects of multiple and long-term seismic load in given point. Calculation of this coefficient was realized for

7 Seismic load of structures in 65 Karvina region that is densely populated. Underground exploitation of black coal is attended by intensive mining induced seismicity. Patterns of curves that represent trends of multiple coefficient C changes document different seismic loads of structures in monitored places. Values of coefficient C in range mean that damages on structures are probably the same as is possible to derive from maximum measured oscillation velocity. Higher values of coefficient C implicate increasing of maximum oscillation velocity for determination of degree of structure damage using the technical standard and consequently increasing of this degree of damage. Unfortunately, it was not possible to document this methodological result by experimental evaluation of failures and other damages on structures. Acknowledgement This outcome has been achieved with the financial support of the Ministry of Education, Youth and Sports of the Czech Republic, project No. 1M0579, within activities of the CIDEAS research centre BIBLIOGRAPHY 1. Czech Technical Standard ČSN Loads of technical structures by technical seismicity. 2. Doležalová H., Holub K., Kaláb Z.: Underground Coal Mining in the Karviná Region and Its Impact on the Human Environment (Czech Republic). Moravian Geographical Report, Vol. 16, No. 2, 2008, p Holečko J., Kaláb Z., Knejzlík J., Ptáček J.: Oscillation velocity on the surface in the Karviná part of the Upper Silesian Coal Basin (Rychlost kmitání povrchu v karvinské části hornoslezské pánve). Journal Uhlí Rudy Geologický průzkum, No. 2/2006 (in Czech), p Kaláb Z.: Evaluation of load on structures cause by mining seismicity for maps of clash of opinions methodology. Zeszyty Naukowe Politechniki Ślaskiej, s. Górnictwo, z. 276, Wydawnictwo Politechniki Śląskiej, Gliwice 2007, s Kaláb Z., Kořínek R. and Hrubešová E.: Technical seismicity as natural extreme in Karviná region. Kwartalnik: Górnictwo i Geologia, t. 4, z. 2a, Wydawnictwo Politechniki Śląskiej, Gliwice, s Knejzlík J., Kaláb Z.: Seismic recording apparatus PCM3-EPC. Publs. Inst. Geophys. Pol. Acad. Sc., No. M-24(340), 2002, p Konečný P., Velička V., Šňupárek R., Takla G., Ptáček J.: Rockbursts in the period of mining activity reduction in Ostrava Karviná Coalfield. ISRM 2003 Technology Roadmap for Rock Mechanics Proceedings, South African Institute of Mining and Metalurgy, Lednická M.: Evaluation of load on structures cause by mining seismicity for maps of clash of opinions first results. Zeszyty Naukowe Politechniki Śląskiej, s. Górnictwo, z. 276, Wydawnictwo Politechniki Śląskiej, Gliwice 2007, s

8 66 Z. Kaláb, M. Lednická Recenzent: Prof. zw. dr hab. inż. Mirosław Chudek, dr h.c. Omówienie W ramach pracy przedstawiono wyniki monitoringu sejsmicznego, prowadzonego w rejonie Karwiny w długim okresie czasu. Wyniki pochodzące z monitornigu były wykorzystane do opracowania nowej metodologii oceny skutków aktywności sejsmicznej wywołanej eksploatacją górniczą z uwzględnieniem długofalowych skutków tych oddziaływań. Zagrożenia z tytułu sejsmiki indukowanej przez podziemną eksploatację górniczą określa się zazwyczaj w Republice Czeskiej przy wykorzystaniu normy technicznej CSN Podstawą do klasyfikacji zagrożenia sejsmicznego wg tej normy jest maksymalna amplituda prędkości wstrząsu, która, przy znajomości typu warstw na poziomie posadowienia obiektu oraz kategorii jego odporności, pozwala określić stopień tego zagrożenia. To podejście bazuje na maksymalnej prędkości fali sejsmicznej, lecz nie uwzględnia wpływu nakładania się efektów sejsmicznych w długich okresach czasu. Problem ten może być rozwiązany za pomocą metodologii przedstawionej w ramach niniejszej pracy. Metodologia ta zakłada przeliczenie maksymalnych prędkości zarejestrowanych fal sejsmicznych z uwzględnieniem liczby wstrząsów, biorąc pod uwagę szczególnie wstrząsy o dużej intensywności. Zaproponowano odpowiednią miarę zagrożenia sejsmicznego w postaci współczynnika C, którego wartości ustala się na podstawie wyników długofalowego monitoringu. Przedstawiony przykład opiera się na danych zarejestrowanych na stacjach sejsmicznych zlokalizowanych na powierzchni w rejonie Karwiny w okresie ostatnich 10 lat.