observation of rotational component in digital data …

GÓRNICTWO I GEOLOGIA 2012 Tom 7 Zeszyt 1

Zdeněk KALÁB1,2), Jaromír KNEJZLÍK1, Markéta LEDNICKÁ1

1 Institute of Geonics, Academy of Sciences of the Czech Republic, 2 Department of Geotechnics and Underground Engineering, Faculty of Civil Engineering

VŠB-Technical University Ostrava,

OBSERVATION OF ROTATIONAL COMPONENT IN DIGITAL DATA OF MINING INDUCED SEISMIC EVENTS

Summary. The Russian pendulous S-5-S seismometer was adapted for measurement of

rotational movement. Output signal can be proportional either to rotational velocity or rotational displacement. Tested measurement was realized in laboratory; in this paper first field measurement with this seismometer is presented. Obtained results document measurable values of rotational movements. The strongest measured values of rotational component exceed 1 mrad.s-1. Values of rotational component of vibration are negligible comparing with values of translation components from viewpoint of structures damages and safe operation of technical equipment.

OBSERWACJE SKŁADOWEJ ROTACYJNEJ W CYFROWYM ZAPISIE WSTRZĄSÓW GÓRNICZYCH

Streszczenie. Wyniki badań prezentowane w niniejszym artykule zostały uzyskane po

zastosowaniu sejsmometru produkcji rosyjskiej do pomiaru ruchów rotacyjnych. W zastosowanym systemie pomiarowym sygnał wyjściowy jest w sposób proporcjonalny uzależniony zarówno od prędkości kątowej, jak i od przemieszczenia kątowego. Wstępne pomiary testowe zostały przeprowadzone w warunkach laboratoryjnych, natomiast artykuł prezentuje wyniki pierwszych pomiarów polowych przeprowadzonych za pomocą opracowanej metody. Uzyskane wyniki obejmują mierzalne wartości ruchów rotacyjnych. Największa uzyskana wartość prędkości kątowej wyniosła 1 mrad/s. Z punktu widzenia bezpieczeństwa konstrukcji i bezpiecznego użytkowania urządzeń technicznych wartości składowej rotacyjnej drgań są pomijalne w porównaniu z wartościami przemieszczeń.

1. Introduction

Current theoretical seismological studies present not only translation components of

ground motions, i.e. Z (vertical), N (north-south), and E (east-west) or R (radial),

T (transversal), and Z (vertical), but also rotational components, i.e. rotation movements

Z. Kalab, J. Knejzlík, M. Lednická

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along Z, N and E axes. Six values of strains complete information for full description of

ground motions (e.g. Pham et al., 2010). The most significant theoretical studies about

rotational seismology were presented by Teisseyre et al. (2006, 2008) and others.

Rotation of the monument to George Inglis (erected in 1850 at Chatak, India) was

observed by Oldham (1899) after the 1897 Great Shillong earthquake of 1897 (Photo from

Oldham, R.D. (1899). Report on the Great Earthquake of 12th June 1897. Mem. Geol. Survey

India, vol. 29; Fig. 1). This monument had the form of an obelisk rising over 60 feet high from

a base of 12 square feet. During the earthquake, the topmost 6-foot section was broken off

and fell to the south and the next 9-foot section was thrown to the east. The rotated remnant is

about 20 feet in length (http://pubs.usgs.gov/of/2007/1145/, http://srl.geoscienceworld.org/

content/80/3/479.figures-only).

Fig. 1. (A) Rotation of the monument to George Inglis, (B) coordinate system for translational velocity, (C) coordinate system for rotational rate, (D) rotated monument. See text for explanation (http://srl.geoscienceworld.org/content/80/3/479.figures-only)

Rys. 1. Obrót pomnika Gorge’a Inglisa (A), układ odnieniesienie dla określania prędkości przemiaeszczeń (B), układ odniesienia dla ruchów obrotowych (C), przekręcony pomnik (D) (http://srl.geoscienceworld.org/content/80/3/479.figures-only)

Three main factors affect the safety of buildings during stronger earthquakes, which are

generally accepted. The material used is the first factor; the shapes of the buildings are the

second one; finally the position of the building has the effect (e.g. Towhata, 2008, Villaverde,

2009). We only emphasize in relation with main topic of this paper that asymmetric shape of

the buildings (second factor) causes that most of these structures will not be able to resist to

Observation of rotational component in digital...

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any rotational movement. Also, some technical equipment (e.g. turbines) is very sensitive to

rotation.

Sensors for measurement of rotational component have been developed in many

institutions (see workshop proceedings of International Working Group on Rotational

Seismology). Russian pendulous S-5-S seismometer can be adapted for measurement of

rotational components of seismic signal. This adaptation was developed in Institute of

Geonics ASCR, Ostrava, Czech Republic in 2010 (Industrial Property Office of Czech

Republic registered Utility model, No. 21679). Output signal can be proportional either to

rotational velocity or rotational displacement. Results from first observation of rotational

component in field are presented in this paper.

2. The S-5-SR seismometer As was mentioned above, S-5-S seismometer (fig. 2) was adapted in Institute of Geonics

ASCR. Detailed description of this adaptation and parameters of adapted S-5-SR seismometer

were presented by Knejzlík et al. (2011, 2012). Main steps of adaptation are possible to

describe as:

• Original balancing spring is removed including its hanging elements.

• Due to static balancing an additional mass is mounted on the magnet of damping

transducer, which is situated on the shorter arm of pendulum.

• Due to dynamic balancing two adjustable counterweights are mounted on the pendulum in

perpendicular directions.

• New electronic elements were added (sensor of angular displacement is included).

• Natural period, damping and zero horizontal position are realized by feedback currents in

coil of the damping electrodynamic transducer.

Basic parameters of the S-5-SR seismometer were determined from laboratory tests using

vibration table in Geophysical Institute in Prague. Natural period of adapted system is 3.3 s

(original natural period was 10 s). Sensitivity constant for angular rate k(dφ/dt) = 52.6 V.s.rad-

1 was obtained in range of oscillation velocity up to 10 mrad.s-1. Sensitivity constant

k(φ) = 1393 V.rad-1 was set for angular displacement channel. Sensitivity constant

kp = 1.1 mV/Hz was taken for ghost sensitivity on translational oscillation of different

frequencies at stationary amplitude 50 µm (peak-peak).


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Fig. 2. Adapted S-5-SR seismometer (uncovered); photo: Kaláb Rys. 2. Zmodyfikowany sejsmometr S-5-Sr (otwarty); fot. Kaláb

3. Field measurement in Orlova station Karvina region is known as area with intensive mining induced seismicity. At this time,

adequate reduction of number and intensity of mining induced seismic events is not observed

in the Karviná region comparing with previous data from seismological monitoring. Damping

program in the Karviná region contributes to selective exploitation due economical reasons.

This exploitation provokes higher load of mining fields and complicated geometry of worked

out spaces. Next reasons are exploitation in deeper seams and necessity of exploitation of

residual coal parts in complicated conditions on contact areas between mined and mined out

spaces. Therefore, intensity of mining induced seismicity is given by current and previous

mining activities (e.g. Martinec et al. 2006, Doležalová et al. 2008, Kaláb et al., 2009, Kaláb

et al., 2011a).

Orlova town in this region was elected to verify the functionality of the sensor S-5-SR in

the field measurement. Foci of mining induced seismic events are localized “under” seismic

station here. The mentioned condition is necessary because the rotational components are

possible to record in epicentre area only, outside of which these components are quickly


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attenuated (e.g. Båth, 1979). From geological point of view, area under discussion is not

covered by Tertiary and Quaternary sedimentary layers (rock outcrop). Two SM-3 horizontal

seismometers (N-S and E-W directions) and S-5-SR rotational seismometer were located in

cellar in big house. Used rotational seismometers detect rotational motion about vertical axis.

Problem, which was determined after installation of seismometers, in this location existed that

residential air conditioning influenced all records. Recorder named PCM3-EPC4 with 100 Hz

sampling frequency of signal was used.

Plenty of mining induced seismic events from near surroundings of Orlova city were

recorded during experimental measurement in 2011-2012. However, only weak events were

recorded. Examples of recorded wave patterns are presented on fig. 3 – fig. 5. Mine, seismic

energy and focus location are from database of Green Gas DPB, a.s., tab. 1. In figures, down

from top are presented rotational component SPIN [mrad.s-1] and two translational horizontal

components (NS and EW), both in [mm.s-1]; maximal values of individual components are

written above wave pattern; time axis (local time synchronized by DCF 77.5 kHz) is the same

for all components. Obtained parameters from the presented wave patterns are summarized in

tab. 2.

Table 1

Location and seismic energy of mining induced seismic events (obtained from database of Green Gas DPB, a.s.) presented on fig. 3 – fig. 5

Date Local time

Mine Seismic energy

[J]

Hypocentre/epicentre distances

[km]

Note

01.1.2012 04:17 Doubrava 9.5E+06 3.8/3.6

29.1.2012 16:50 Doubrava 5.6E+04 2.2/2.0 Blasting operation

22.2.2012 06:26 Doubrava 3.3E+04 3.7/3.6

Table 2

Summary of parameters of mining induced seismic events presented on fig. 3 – fig. 5

Date Local time

Rotational component

SPIN [mrad.s-1]

Translational horizontal comp.

NS [mm.s-1]

Translational horizontal comp.

EW [mm.s-1] 01.1.2012 04:17 0.1514 1.4766 2.2969

29.1.2012 16:50 0.0424 0.2144 0.4883

22.2.2012 06:26 0.0367 0.2300 0.5078


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Fig. 3. Records of mining induced seismic event from Doubrava Mine, 01.01.2012; down from top: rotational component SPIN [mrad.s-1] and two translational horizontal components (NS and EW), both in [mm.s-1]; horizontal axis is local time [s]

Rys. 3. Zapis wstrząsu wygenerowanego w kopalni „Dobrawa”, 1.01.2012; od góry kolejno: składowa rotacyjna SPIN [mrad/s] i dwie składowe przemieszczeniowe w kierunkach poziomych (północno-południowym i wschodnio-zachodnim) [mm/s]; na osiach poziomych oznaczono czas lokalny [s]


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Presented wave patterns are possible to divide into two types. The strongest event was

recorded on 1 January 2012. This event was felt by inhabitants in epicentre area, especially in

higher levels of panel buildings. The third event originated in the same focus area but with

much lower seismic energy. Second type represented by second event originated after blast


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operation in overburden of mined coalface, it means that it is not typical mining induced

seismic event.

Records of rotational components of all recorded events are different from records of

horizontal translation components. Character of rotational vibrations is very similar like

character of translation vibrations. Therefore, we will use common seismological software for

interpretation of measured data (e.g. Kaláb et al., 2011b). Duration of vibration effect of

rotational movement is comparable with duration of translation one. The strongest measured

values exceed 1 mrad.s-1 (this record is not presented here). To compare spectra of rotational

and translation components, rotational components have usually lower spectral amplitudes

and also slightly different frequency composition. It is necessary to add that character of these

wave patterns can be probably markedly influenced by response of building, in which

seismometers were located.

4. Conclusion In this paper, first information about field measurement of rotational vibration with new

developed S-5-SR seismometer is presented. The main aim of this experiment was to obtain

information about usability of this one in field measurement. Of course, recordings of

rotational movement generated in epicentre area with mining induced seismicity are very

important result. The strongest measured values of rotational component exceed 1 mrad.s-1.

This measurement confirmed that vibration generated by mining operations produce also

measurable rotational movement.

Values of rotational component of vibration are negligible comparing with values of

translation components from viewpoint of structures damages and safe operation of technical

equipment. Significance of rotational movement increases during very strong earthquakes in

epicentre areas, as many examples from references are documented.

This work was realized in frame of project CzechGeo project (LM2010008) that is closely

related with the 7th FP project EPOS (European Plate Observing System).


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BIBLIOGRAPHY

1. Båth M.: Introduction to seismology. Birkhauser Verlag, Basel 1979. 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. 14-24.

3. Kaláb Z., Kořínek R., Hrubešová E.: Technical seismicity as natural extreme in Karviná region. Kwartalnik ”Górnictwo i Geologia”, t. 4, z. 2a, 2009, s. 87-94.

4. Kaláb Z., Kořínek, R., Hrubešová E., Lednická M.: Vibration on the surface due underground mining in Karviná region, Czech Republic. [In]: 6th Congress of the Balkan Geophysical Society, Conference Proceedings and Exhibitors´ Catalogue, Budapest, Hungary, 2011a, CD.

5. Kaláb Z., Lednická. M., Lyubushin A.A.: Processing of Mining Induced Seismic Events by Spectra Analyzer Software. Kwartalnik „Górnictwo i Geologia”, t. 6, z. 1, 2011b, s. 75-83.

6. Knejzlík J., Kaláb Z., Rambouský Z.: Adaptation of pendulous seismometer S-5-S for measurement of rotation component of seismic vibrations. International Journal of Exploration Geophysics, Remote Sensing and Environment (EGRSE), Vol. XVIII.3, 2011, p. 72-79 (in Czech).

7. Knejzlík J., Kaláb Z., Rambouský Z.: Concept of pendulous S-5-S seismometer adaptation for measurement of rotational ground motion. Journal of Seismology, DOI: 10.1007/s10950-012-9279-6, 2012.

8. Martinec et al.: Termination of underground coal mining and its impact on the environment. ANAGRAM, Ostrava 2006.

9. Pham N.D., Igel H., de la Puente J., Kaser M., Schoenberg M.A.: Rotational motions in homogeneous anisotropic elastic media. Geophysics, Vol. 75(5), 2010, D47-D56.

10. Teisseyre R., Nagahama H., Majewski E.: Physics of asymmetric continua: Extreme and fracture processes: Earthquake rotation and soliton waves. Springer-Verlag, Berlin & Heidelberg 2008.

11. Teisseyre R., Takeo M., Majewski E. (eds.): Earthquake source asymmetry, structural media and rotation effects. Springer-Verlag, Berlin & Heidelberg 2006.

12. Towhata I.: Geotechnical earthquake engineering. Springer-Verlag, Berlin & Heidelberg 2008.

13. Villaverde R.: Fundamental concept of earthquake engineeting. CRC Press, Taylor & Francis Group, 2009.

Omówienie

W artykule zaprezentowano wstępne wyniki eksperymentalnych pomiarów sejsmiczności pochodzenia górniczego w regionie karwińskim w 2011 roku. Zmierzone wartości składowej poziomej dochodziły do 1 mrad/s, przy czym energia sejsmiczna tych wstrząsów nie przekraczała wartości 105 J, a odległość hipocentralna dochodziła do 2 km. Z punktu widzenia zagrożenia dla obiektów budowlanych i bezpieczeństwa urządzeń technicznych wartości składowej rotacyjnej drgań są pomijalne w porównaniu z wartościami przesunięć. Natomiast, jak wskazują na to liczne przykłady prezentowane w publikacjach, znaczące przyrosty ruchów rotacyjnych mają miejsce podczas silnych trzęsień ziemi.


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Do badań rotacyjnych ruchów gruntu zaadaptowany został rosyjski elektrodynamiczny sejsmometr o nazwie S-5-S. W artykule w skrócie przedstawiono główne informacje na temat zastosowanego sejsmometru i jego modyfikacji. W celu zbadania jego nowych właściwości oraz skalibrowania podstawowych parametrów przeprowadzone zostały testy laboratoryjne. Do badań wykorzystano stół wibracyjny, mieszczący się w Instytucie Geofizyki ASCR w Pradze. Za pomocą tego urządzenia ustalono parametry sejsmometru zarówno dla ruchów rotacyjnych, jak i przemieszczeń.

observation of rotational component in digital data …

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