REGIONAL GEODYNAMIC NETWORK HIGHLANDS, THE BOHEMIAN MASSIF

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1 Acta Geodyn. Geomater., Vol. 4, No. 4 (148), , 2007 REGIONAL GEODYNAMIC NETWORK HIGHLANDS, THE BOHEMIAN MASSIF Zdeňka SCHENKOVÁ *, Vladimír SCHENK, František MANTLÍK and Milada GRÁCOVÁ Institute of Rock Structure and Mechanics, Academy of Science of the Czech Republic, v.v.i., V Holešovičkách č 41, CZ Prague 8, Czech Republic *Corresponding author s zdschenk@irsm.cas.cz (Received August 2007, accepted November 2007) ABSTRACT To investigate recent crustal movements between northern and southern parts of Moravo-Silesian region of the Bohemian Massif and to find their relation to movements of structure blocks of Moldanubicum, it was decided to establish a regional geodynamic network HIGHLANDS. Seven sites for monitoring GPS signals were built with respect of geological and geophysical materials in the southern area of the Českomoravská vysočina Highlands. So far two epoch 48-hours GPS measurements have been performed in 2005 and 2006 with Ashtech receivers and antennas. GPS monitored data were processed by the Bernese software v The rather preliminary site movements were assessed and discussed from the viewpoint of recent geodynamic motions. KEYWORDS: epoch GPS measurements, geodynamics, Českomoravská vysočina Highlands, the Bohemian Massif 1. INTRODUCTION In the last years the stress field model of the Bohemian Massif and its surroundings was established that allowed possible geodynamic mobility trends among individual structural block of the Massif to be forecasted (Schenk et al., 1997, 1998a, 1998b; Vyskočil and Schenk, 1998). There are three independent approaches that can detect low mobility trends directly in the field: (i) a measurement of the Global Positioning System (GPS) satellite signals at specially built up site monuments of geodynamic networks, (ii) a monitoring of earthquakes at local networks and/or arrays and (iii) a geological mapping of recent tectonic movements. At present monitoring GPS signals is widely used in the site position determination. From 1997 till 2001 two regional geodynamic networks, EAST SUDETEN (Schenk et al., 2002a, 2003) and WEST SUDETEN (Schenk et al., 2002b, 2006), consisting altogether 22 sites were built on which annual epoch measurements have been performed. A setting up of the individual GPS geodynamic sites was done with respect to the neighbouring GPS network SNĚŽNÍK (Švábenský and Weigel, 1999) and the Polish GEOSUD (Cacoń and Dyjor, 1999) and KARKONOZSE (Kontny et al., 2002, 2004) networks. The regional HIGLANDS geodynamic network was established in 2005 in the south area of the Českomoravská vysočina Highlands. It is linked to two regional geodynamic EAST and WEST SUDETEN networks mentioned above, which investigate geodynamic motions between Lugian and Moravo-Silesian units of the Bohemian Massif. Processing annual epoch measurements on both SUDETEN networks revealed mostly sinistral motions along the Moravo-Silesian NNE-SSW faults and thrusts induced by recent geodynamic pushing of Alpine tectonic structures on the Bohemian Massif (Schenk et al., 2003). The GPS sites of the EAST SUDETEN, WEST SUDETEN and HIGHLANDS geodynamic networks together with the GEONAS network of the Academy of Science of the Czech Republic of permanent stations (Mantlík et al., 2006) are drawn in Figure GEODYNAMIC NETWORK HIGHLANDS To assess the stress field and motion pattern of structural units situated between the Alps and the Lugian and the Moravo-Silesian units altogether seven sites were built in the Moldanubian pluton (Peklůvko PEKL and Pavlov - PAVL), in the Svratka anticline (Osiky - OSIK and Zábludov - ZABL), in the Třebíč Massif (Benetice - BENE), in the Brno Massif (Hořice - HORI), and in southern part of the Moravian- Silesian Palaeozoics (Nové Sady - NOSA); see Figure 1 and Table 1. The sites were chosen with respect to known geological materials and geophysical data.

2 208 Z. Schenková et al. Table 1 Sites of the regional geodynamic network HIGHLANDS and their geographic coordinates. Site Latitude Longitude Elipsoidal height BENE BRAD HORI NOSA OSIK PAVL PEKL RUDN ZABL The construction of GPS sites of the HIGHLANDS geodynamic network is the same like the EAST SUDETEN and WEST SUDETEN geodynamic network sites. A concrete rectangular block with a base of 40x40 cm and a height from 60 to 100 cm was built on every site. On its top a steel plate with a screw thread for a GPS antenna was cemented. Every block has a firm anchored contact with bedrock. 3. GPS DATA PROCESSING Two epoch GPS measurements were realized on all seven sites of the HIGHLANDS network and on two selected sites BRAD and RUDN of the EAST SUDETEN network in two full day sessions (48 hours) on September 2005 and on September For the site OSIK only data of three GPS days were available and, thus, the processing of its records gave rather raw assessment of geodynamic movement. GPS epoch measurements were performed with Ashtech receivers equipped by geodetic, marine and choke-ring antennas, respectively (Table 2) powered by 12V/165Ah batteries. Signals were recorded with sampling rate of 30 seconds. Monitored GPS data sampled in 30 sec intervals were processed jointly with data of the permanent EPN station GOPE. Raw data were transferred into the RINEX format and processed by the Bernese software v. 5.0 (Hugentobler et al., 2005) under the following assumptions: Precise satellite orbits, satellite clock data and the Earth s rotation parameters were used from Centre for Orbit Determination in Europe (CODE), Bern. Geocentric and geographic coordinates were computed in the ITRF2000 reference frame. Table 2 HIGHLANDS geodynamic network sites and their receivers and antennas. Site Receiver Antenna Type S/N Type S/N Height [m] BENE Ashtech Z marine BRAD Ashtech Z geodetic HORI Ashtech Z marine NOSA Ashtech Z marine OSIK Ashtech Z-12 surveyor geodetic PAVL Ashtech Z geodetic PEKL Ashtech Z-12 X-treme marine RUDN Ashtech Z geodetic ZABL Ashtech Z-12 surveyor marine

3 REGIONAL GEODYNAMIC NETWORK HIGHLANDS, THE BOHEMIAN MASSIF 209 Antenna phase centre characteristics were taken over from the US National Geodetic Survey Geosciences Research Division. The stochastic ionosphere model GLOBAL (CODgpswd.ION) was applied for ionosphere correction estimation. Baselines were fixed for each observation GPS day. Linear combinations of observations L3 (ionosphere free) were included. The QIF (Quasi Ionosphere Free) strategy for ambiguity resolution was chosen. The atmosphere model DRY NIELL was used for troposphere correction estimation. To obtain preliminary site movement velocities the constrained network solution for each observation GPS day was computed using three EPN permanent stations BOR1, PENC and ZIMM (Fig. 3). Final combinations of daily solutions were determined by means of the ADDNEQ2 program. 4. PRELIMINARY SITE MOVEMENT VELOCITIES The movement velocities of individual sites were determined only from the measurements of two years (2005 and 2006). It is clear that further GPS epoch monitoring is needed to increase reliability of approximations of the horizontal and/or vertical movements. To find differences between the movements of individual sites of the HIGHLANDS network three following sites step by step were fixed: GOPE. RUDN and PAVL. Always the movement vector of one of three above mentioned sites was subtracted from the movement vectors of all sites. In this way three pictures of site movement velocities were obtained (Figs. 4a, b and c). When the permanent EPN station GOPE was selected like the reference site (Fig. 4a), the movements of the HIGHLANDS sites are directed mostly in the south-east direction. It denoted that movements between GOPE site and the HIGHLANDS sites are generally opposite and reached as much as 1 cm per year. It could be denoted that the area is under any lengthening or opening process. Nevertheless it is too early now to start with any regional explanations and it is necessary to wait for next annual epoch measurements. For the reference site RUDN (Fig. 4b) the ZABL and HORI sites located close to the Boskovice Furrow exhibit a sinistral movement of 1 2 mm per year along the Furrow. Since the sinistral movements have been detected already on the faults of the Moravian tectonic system, it is possible to assume that the sinistral movement trends dominate on many faults situated in close vicinity of the contact of the Moldanuabian and Lugian parts and the Moravo- Silesian part of the Bohemian Massif. Finally, when the PAVL site situated in the centre of the HIGHLANDS geodynamic network was selected like the reference site (Fig. 4c), then sites GOPE and PEKL display dominant west movement components while the sites BENE, HORI, NOSA, RUDN and ZABL display prevailing the east movement components. The sinistral movement along the Boskovice Furrow was also identified. 5. CONCLUSIONS Two 48-hour GPS epoch measurements on seven sites of the HIGHLANDS geodynamic network (BENE, HORI, NOSA, OSIK, PAVL, PEKL and ZABL) and two sites of the WEST SUDETEN network (BRAD, RUDN) were used to assess very preliminary site movement velocities. For two campaigns neither their standard deviations could be computed nor time series of individual site positions drawn. The monitored GPS satellite signals were processed jointly with data of the permanent station GOPE and were constrained to three EPN stations BOR1, PENC and ZIMM. Relative site movement velocities, when three different sites were fixed, are presented. Generally, the preliminary analysis of movements displayed that eastern part of the Bohemian Massif could be under slight extending trends, but this finding has to be proved by other GPS measurements. The detection of sinistral movements of 1 2 mm/year along the faults situated between the Moldanubian and Moravian parts of the Bohemian Massif (area of the Boskovice Furrow) verified the previous results from the northern part of Moravo- Silesian structural block. It is evident that these very preliminary detected movements have to be verified by other three/four GPS measurements before any geological and/or tectonic interpretations will be started. ACKNOWLEDGEMENTS The authors express their thanks to the Grant Agency of the Academy of Sciences of the Czech Republic for the financial support (Project IAA ) that help them to build the geodynamic network HIGHLANDS and to realize the epoch measurements. Activities connected with the project were also partly supported by the Ministry of Education. Youth and Sport of the Czech Republic (Projects LC506 and 1P05ME781). The authors are greatly appreciated to the firms GEOOBCHOD Pardubice, ČESKÝ TELECOM Hradec Králové, PROGEO Jihlava and namely to Aleš Rucký for the close collaboration in the GPS signal monitoring and to AKUMA Mladá Boleslav for perfect battery power operations. They wish to extend their sincere thanks to all persons who participated in the GPS epoch measurements in 2005 and 2006.

4 210 Z. Schenková et al. REFERENCES Cacoń, S. and Dyjor, S.: 1999, Neotectonic and recent movements of the Earth s crust in Polish part of the Sudeten and the Fore-Sudetic block. Exploration Geophysics, Remote Sensing and Environment 6, No. 2, Hugentobler, U., Dach, R., Fridez, P. and Mendl, M. (eds.): 2005, Bernese GPS software version 5.0, Astronomical Inst., Univ. of Bern, 466. Kontny, B., Bosy, J. and Makolski, K: 2002, Geodynamic GPS network Karkonosze Preliminary results of the campaign Acta Montana, Ser. A, No. 20(124), Kontny, B.. Bosy, J. and Makolski, K.: 2004, Local geodynamic network KARKONOSZE The results of three years of measurements and first interpretations. Acta Geodyn. Geomater. 1, No. 3(135), Mantlík, F., Schenk, V., Schenková, Z., Kottnauer, P. and Fučík, Z.: 2006, Network of the Academy of Science of the Czech Republic (GEONAS). Permanent GPS observations, their remote control and transfer to data centres. Geoph. Res. Abstracts 8, G6-1 WE Mísař, Z., Dudek, A., Havlena, V. and Weiss, J.: 1983, Regional geology of the Czech Republic (in Czech), SPN, Praha, 333. Schenk, V., Cacoń, S., Bosy, J., Kontny, B., Kottnauer, P. and Schenková, Z.: 2002a, The GPS network SUDETEN Five annual campaigns ( ). Data processing and results. Acta Montana, Ser. A, No. 20(124), Schenk, V., Kottnauer, P., Schenková, Z., Rucký. A., Pšenička, J., and Řehák, J. jr.: 2002b, Regional geodynamic network WEST SUDETEN. A westward wide-ranging extension of present EAST SUDETEN network. Acta Montana, Ser. A, No. 20(124), Schenk, V., Schenková, Z., Cacoń, S., Kontny, B., Bosy, J. and Kottnauer, P.: 2003, To geodynamic interpretations of GPS data monitored on the EAST SUDETEN network. Acta Montana, Ser. A, No. 24(131), Schenk, V., Schenková, Z., Grácová, M. and Kottnauer, P.: 2006, Preliminary site movements in the GPS West Sudeten network. Acta Geodyn. Geomater. 3, No. 3(143), Schenk, V., Schenková, Z. and Kottnauer, P.: 1997, Quantitative seismotectonic analysis of the Bohemian Massif, Czech Republic. Exploration Geophysics, Remote Sensing and Environment 4, No. 1, Schenk, V., Schenková, Z. and Kottnauer, P.: 1998a, Geodynamical pattern of the Bohemian Massif. In: The Bohemian Massif. CEI CERGOP Study Group N.8 Geotectonic Analysis of the Region of Central Europe. Report on Geodesy 33, No. 3, Warsaw Univ. of Technology, Warsaw, Schenk, V., Schenková, Z. and Kottnauer, P.: 1998b, Assumed regional field stress pattern in the geodynamic model of the Bohemian Massif (in Czech). In Kaláb Z. (ed.). Současné směry v seismologii a inženýrské geofyzice. Sb. referátů regionální konference, Ústav geoniky AV Č R, Ostrava, Švábenský, O. and Weigel, J.: 1999, Local geodynamic network SNĚŽNÍK. Exploration Geophysics, Remote Sensing and Environment 6, No. 2, 4-7. Vyskočil, P. and Schenk, V.: 1998, Geological and geophysical studies and crustal structure in the Bohemian Massif. In: The Bohemian Massif. CEI CERGOP Study Group N.8 Geotectonic Analysis of the Region of Central Europe. Report on Geodesy 33, No. 3, Warsaw Univ. of Technology, Warsaw

5 Z. Schenková et al.: REGIONAL GEODYNAMIC NETWORK HIGHLANDS, THE BOHEMIAN MASSIF Fig. 1 Permanent stations of the GEONAS (blue and navy-blue points) and TOPNET (green points) geodynamic networks; GPS sites of regional geodynamic WEST SUDETEN, EAST SUDETEN (red points for both networks) and HIGHLANDS (purple points) networks are displayed on a simplified geological map compiled by Mísař et al. (1983); by black points are marked stations involved into the European GPS permanent network (EPN). BENETICE HOŘICE OSIKY PEKLŮVKO Fig. 2 Construction scheme of GPS site (right) and photos of four GPS sites of the HIGHLANDS geodynamic network.

6 Z. Schenková et al.: REGIONAL GEODYNAMIC NETWORK HIGHLANDS, THE BOHEMIAN MASSIF Fig. 3 Baselines used for GPS data processing on the HIGHLANDS geodynamic network. GOPE fixed Fig. 4a

7 Z. Schenková et al.: REGIONAL GEODYNAMIC NETWORK HIGHLANDS, THE BOHEMIAN MASSIF RUDN fixed Fig. 4b PAVL fixed Fig. 4c Fig. 4 Annual GPS velocity movements for the HIGHLANDS network sites determined from two epoch measurements of the period when (a) the permanent GOPE station. (b) the epoch RUDN site and (c) the epoch PAVL site were fixed; blue points network sites, green points - reference station or sites, and arrows site movement velocities.