NON-REVIEWED CONTRIBUTION

Stud. Geophys. Geod., 52 (2008), 439−448 439 © 2008 Inst. Geophys. AS CR, Prague

PASSEQ 2006−2008: PASSIVE SEISMIC EXPERIMENT IN TRANS-EUROPEAN SUTURE ZONE

M. WILDE-PIÓRKO1, W.H. GEISSLER2, J. PLOMEROVÁ3, M. GRAD1, V. BABUŠKA3, E. BRÜCKL4, J. CYZIENE5, W. CZUBA6, R. ENGLAND7, E. GACZYŃSKI6, R. GAZDOVA13, S. GREGERSEN8, A. GUTERCH6, W. HANKA9, E. HEGEDŰS10, B. HEUER9, P. JEDLIČKA3, J. LAZAUSKIENE5,17, G. RANDY KELLER11, R. KIND9, K. KLINGE12, P. KOLINSKY13, K. KOMMINAHO14, E. KOZLOVSKAYA15, F. KRÜGER16, T. LARSEN8, M. MAJDAŃSKI6, J. MÁLEK13, G. MOTUZA17, O. NOVOTNÝ13, R. PIETRASIAK6, TH. PLENEFISCH12, B. RŮŽEK3, S. SLIAUPA5, P. ŚRODA6, M. ŚWIECZAK6, T. TIIRA14, P. VOSS8 AND P. WIEJACZ6

1 University of Warsaw, Warsaw, Poland (mwilde@igf.fuw.edu.pl)

2 Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

3 Institute of Geophysics, Acad. Sci. Czech Rep., Praha, Czech Republic

4 Vienna University of Technology, Vienna, Austria

5 Geological Survey of Lithuania, Vilnius, Lithuania

6 Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland

7 University of Leicester, Leicester, Great Britain

8 Geological Survey of Denmark and Greenland, Copenhagen, Denmark

9 GeoForschungsZentrum Potsdam, Potsdam, Germany

10 Eötvös Loránd Geophysical Institute, Budapest, Hungary

11 University of Oklahoma, Norman, USA

12 Seismological Central Observatory, Erlangen, Germany

13 Institute of Rock Structure and Mechanics, Acad. Sci. Czech Rep., Praha, Czech Republic

14 University of Helsinki, Helsinki, Finland

15 University of Oulu, Oulu, Finland

16 University of Potsdam, Potsdam, Germany

17 University of Vilnius, Vilnius, Lithuania

1. INTRODUCTION

PASSEQ 2006−2008 project (PASsive Seismic Experiment in TESZ) aims at studying the lithosphere-asthenosphere system around the Trans-European Suture Zone (TESZ) - the transition between the old Proterozoic platform of northern and eastern Europe and younger Phanerozoic platform in central and western Europe. PASSEQ 2006−2008 project is linked with the TOR project (Gregersen et al., 2002). The TOR passive seismic experiment was realized during 1996-97 and seismic research focused on the north-western part of TESZ. PASSEQ 2006−2008 focuses on central part of TESZ area in Poland, mainly the Teisseyre-Tornquist Zone (TTZ), following the margin of the East European Craton. In Poland, TTZ is well defined 50−100 km wide zone, while the precise

NON-REVIEWED CONTRIBUTION

440 Stud. Geophys. Geod., 52 (2008)

location of the boundary between the lithospheric plates of Baltica and Avalonia in the north-western segment of TESZ is still under discussion. There, the TESZ splits into two branches: Thor Suture (TS) in the south and Sorgenfrei-Tornquist Zone (STZ) in the north (e.g. Pharaoh et al., 1997; Grad et al., 2002; Dadlez et al., 2005). Much of Poland and northern Germany are covered by a deep (up to 10 km) basin, usually called the Permian basin or Polish-North German basin that was filled with Permian and Mesozoic sediments during a phase of extension after the Variscan orogeny. In northern Poland the basin is called the Mid-Polish Trough and parallels the edge of the East European Craton. During the Alpine orogeny it experienced tectonic inversion.

Our knowledge of deep structure of the TTZ is very important for understanding the tectonic processes that affected central Europe. The TTZ is visible as a major change in the crustal/lithospheric structure in seismic, magnetic, and gravity fields as well as in heat flow studies. The results of global seismic tomographic analysis (Zielhuis and Nolet, 1994) show that TTZ in Poland is a narrow transition zone dividing the area of high shear-wave velocities in the upper mantle beneath the East European platform from the area of low shear-wave velocities beneath the Palaeozoic platform. Futhermore, the structure of the crust differs - the East European platform in the NE Poland is characterized by a 0.5 to 5 km thick sedimentary cover, a 42 to 47 km thick crust, and relatively low heat flow < 40 mW/m2. The crust of the Palaeozoic platform in SW Poland is characterized by a 7 to 12 km thick sedimentary cover, a thinner 28 to 34 km thick crust with much higher heat flow between 50 and 70 mW/m2 (e.g. Majorowicz et al., 2003; Guterch et al., 2004). The upper mantle beneath the TTZ seems to be about 0.1 g/cm3 denser than beneath the neighbouring regions of the Fore-Sudetic monocline and the East European platform (e.g. Grabowska et al., 1991). It was also observed that the seismic energy does not propagate across the TTZ from regional seismic events, which could be the indication of a root of TTZ reaching at least a depth of about 200 km (Schweitzer, 1995; Wilde-Piórko et al., 1999). Meier and Malischewsky (1997) reported the reflection of surface waves coming from SW at the TTZ. The TESZ appears also as a distinct boundary between two regions of different upper mantle fabric (Babuška et al., 1998). It was observed that the mantle transition zone might be thicker than average thickness beneath the Precambrian platform, which indicates lower temperatures of the transition zone between “410” and “660” km boundaries concurring with colder lithosphere above (Świeczak et al., 2004). A much thinner mantle transition zone was observed beneath the Palaeozoic platform and the Carpathians by the same studies indicating higher temperatures between 410 and 660 km depths. However, a recent receiver function study, analysing data from sparsely located permanent broad-band seismic stations, observed normal thickness of the mantle transition zone beneath the Precambrian and Palaeozoic platforms (indicating normal temperature), whereas the transitions zone beneath the Carpathians and the Pannonian Basin seems to be thickened, indicating low temperatures as it can be expected in a subduction zone environment (Geissler et al., 2008). One of the goals of the present project is to solve this discrepancy.

NON-REVIEWED CONTRIBUTION

Stud. Geophys. Geod., 52 (2008) 441

2. DESCRIPTION OF THE STATION ARRAY

PASSEQ 2006−2008 experiment could be realized thanks to a great international effort of 17 institutions from 10 countries. To investigate the structure of the crust and upper mantle about 200 temporary seismic stations were installed along about 1200 km long and about 400 km wide array from Germany throughout Czech Republic and Poland to Lithuania (Fig. 1 and Table 1) operating for about 2 years. The array is centred along the POLONAISE’97 profile P4 with an excellent knowledge of seismic structure of the crust and uppermost mantle (Grad et al., 2003). The average spacing between stations is about 60 km, while along central profile it is only about 20 km. A total of 147 three-component temporary short-period and 49 temporary broad-band seismic stations provided the continuous recordings from May 2006 to June 2008 with a main core of recording in 2007. The array includes also permanent stations of national observatories located within the area of experiment. The configuration of the seismic network is a compromise to satisfy the needs of different seismic methods. A dense central profile allows a use of modern passive 2-D imaging techniques. The distribution of broad-band sensor is designed for surface wave and receiver function studies of the upper mantle down to the mantle transition zone in a wide frequency ranges and will allow us to estimate 3-D effects.

Frequency sampling was 20, 50 or 100 Hz, depending on a type of data loggers. The stations were installed in quiet sites like forest houses, castles, cloisters, small farms, etc., in the basement or on the ground in buildings with concrete floor (Fig. 2). The stations supplied by local power cuts encountered problems with starting up the stations and timing of GPS. The stations were serviced every 1 to 5 months depending on type of data

Table 1. Temporary seismic stations contributing to PASSEQ 2006−2008 project.

Institution Broad-Band

Stations Short-Period

Stations

Geological Survey of Denmark and Greenland, Copenhagen, Denmark 4 -

Geophysical Instrument Pool, Potsdam, Germany 10 60

Institute of Geophysics ASCR, Prague, Czech Republic 11 13

Institute of Geophysics PAS, Warsaw, Poland - 19

Institute of Rock Structure and Mechanics ASCR, Prague, Czech Republic

6 -

Eötvös Loránd Geophysical Institute, Budapest, Hungary - 8

PASSCAL Instrument Centre, Socorro, USA - 20

SEISUK, University of Leicester, Leicester, Great Britain 10 -

University of Helsinki, Helsinki, Finland - 8

University of Oulu, Oulu, Finland - 6

University of Potsdam, Potsdam, Germany - 13

Seismological Central Observatory, Erlangen, Germany 4 -

Vienna University of Technology, Vienna, Austria 4 -

NON-REVIEWED CONTRIBUTION

442 Stud. Geophys. Geod., 52 (2008)

logger and a compromise between possibilities of station visits and data loss. Locations of the individual temporary seismic stations, types of instruments and time of operation are listed in http://geofon.gfz-potsdam.de/db/station.php and http://www.ig.cas.cz/~passeq.

3. DATA PROCESSING

All raw data from temporary seismic stations are archived in their original formats at

least on two different media by each group operating the stations. Additionally, all continuous data are converted to miniseed format and with transfer functions of sensors and data loggers (dataless volumes) stored in GEOFON Data Centre in Potsdam. According to the group agreement, all continuous data will be available for members of PASSEQ Working Group online, exclusively for three years after the database will be completed and then open for scientific community.

Fig. 1. Location of PASSEQ 2006−2008 seismic experiment around the Trans-European Suture Zone (TESZ) - 1, 2 - permanent broad-band and short-period seismic stations of national and regional observatories; 3, 4 - temporary broad-band stations and temporary short-period stations.

NON-REVIEWED CONTRIBUTION

Stud. Geophys. Geod., 52 (2008) 443

During the two-year period of operating the PASSEQ 2006−2008 array, more than 1700 teleseismic events with magnitude larger than 5.0 have been recorded (Fig. 3). Due to a large variety of methods planned to be used, several different event-oriented databases containing both teleseismic and local events will be created by joint effort of groups using the same data. We present examples of seismograms of a teleseismic earthquake from Kuril Islands, which occurred on 15th of November 2006 and was recorded by broad-band (Fig. 3) and short-period seismic stations (Fig. 4). Fig. 5 shows an example of a local event from the Lubin cooper mine in south-western Poland on 14th of October 2006.

Fig. 2. Examples of installation sites of PASSEQ 2006−2008 temporary seismic stations: short-period one in Frankenberger Höhe, Franken, Germany (top) and broad-band one in Żeliszewo, Western Pomerania (Zachodnio-Pomorskie), Poland (bottom).

NON-REVIEWED CONTRIBUTION

444 Stud. Geophys. Geod., 52 (2008)

4. METHODS OF INTERPRETATION

Main goal of PASSEQ 2006−2008 passive seismic experiment is a detailed investigation of the 3-D upper mantle structure around the TESZ region in Central Europe, structure of the lower lithosphere and asthenosphere, the lithosphere-asthenosphere boundary, “410” and “660” km discontinuities in transition zone from East European Craton to Variscan Europe. Data from the dense array of stations will allow us to map the upper mantle structure, e.g., the contrast, sharpness and topography of seismic discontinuities, with much higher precision than it was possible by using different techniques (e.g., by P and S receiver functions) up to now. We will strongly capitalize on excellent knowledge of the structure of the crust particularly beneath Poland, coming from dense active refraction/reflection measurements (e.g., Grad et al., 2002, 2003; Guterch et al., 2004). By applying body- and surface-wave tomography, as well as the receiver function techniques, we expect to reveal variations of seismic velocities within the upper mantle around the contact zone of the Precambrian platform and younger mobile belts down to the upper-mantle transition zone. Analysis of shear wave splitting of teleseismic SKS waves, P residual analysis and converted waves will resolve variations of anisotropy across the TTZ. Joint inversions of independent datasets will provide more realistic 3-D

Fig. 3. Distribution of epicentres of teleseismic events during May 2006 − May 2008 period plotted relatively to a position of PASSEQ 2006−2008 array.

NON-REVIEWED CONTRIBUTION

Stud. Geophys. Geod., 52 (2008) 445

models of the upper mantle than single methods. We believe we will be able to contribute towards answering some of the important questions such as: What is the depth and structure of the lithosphere-asthenosphere boundary? What about existence of a tectosphere beneath the craton in the east? What are thermal properties of the mantle transition zone? Are there any coherent relations between observed mantle anisotropy and the topography of the LAB due to its possible impact on the mantle flow regime?

Acknowledgements: In Poland, PASSEQ 2006-2008 experiment was funded by Ministry of

Scientific Research and Information Technology, State Committee for Scientific Research (Grant No. 2 P04D 083 29) and supported by Institute of Geophysics Polish Academy of Sciences. The research of Czech Republic team is supported by the Grant Agency of the Czech Academy of Sciences (Grant No. IAA300120709). The fieldwork of the German team was supported by the involved institutes, the German Science Foundation and the colleagues from the University of Leipzig. We very much appreciate the Geophysical Instrument Pool of the GeoForschungsZentrum Potsdam for providing 60 short-period and 10 broad-band seismic stations as well as the GEOFON program for providing us with a comfortable database. Especially, we thank S. Hemmleb, K.-H. Jäckel, M. Brunner and E. Wetzig for their help during the operation and archiving.

Fig. 4. Examples of vertical components of seismograms of a teleseismic earthquake from Kuril Islands region recorded by some of PASSEQ 2006−2008 broad-band seismic stations. Station codes and epicentre distances are indicated to the right of the traces. Focal parameters from USGS/NEIC PDE Catalogue: 2006/11/15, 11:14:13.57 UTC, latitude 46.59°N, longitude 153.27°E, depth 10 km, Mw = 8.3. Time 0.0 refers to 5 minutes after the origin time. All traces are normalized to maximum amplitudes.

NON-REVIEWED CONTRIBUTION

446 Stud. Geophys. Geod., 52 (2008)

References

Babuška V., Montagner J.-P., Plomerová J. and Girardin N., 1998. Age-dependent large-scale fabric of the mantle lithosphere as derived from surface-wave velocity anisotropy. Pure Appl. Geophys., 151, 257−280.

Dadlez R., Grad M. and Guterch A., 2005. Crustal structure below the Polish Basin: Is it composed of proximal terranes derived from Baltica? Tectonophysics, 411, 111−128.

Geissler W.H., Kind R. and Yuan X., 2008. Upper mantle and lithospheric heteroheneities in Central and Eastern Europe seen by teleseismic receiver functions. Geophys. J. Int., 174, 351−376, doi: 10.1111/j.1365-246X.2008.03767.x.

Grabowska T., Koblański A. and Dolnicki J., 1991. Deep structure of the Earth's crust in the Teisseyre-Tornquist Zone (TTZ) in Poland, based on magnetic and gravity studies. Publs. Inst. Geophys. Pol. Acad. Sc., A-20(255), 81−89.

Grad M., Guterch A. and Mazur S., 2002. Seismic refraction evidence for crustal structure in the central part of the Trans-European Zone in Poland. In: Winchester J.A., Pharaoh T.C. and Verniers J. (Eds.), Palaeozoic Amalgamation of Central Europe. Geol. Soc. London Spec. Publ., 201, 295−309.

Fig. 5. Examples of vertical components of seismograms of a teleseismic earthquake from Kuril Islands region (and aftershocks) recorded by selected PASSEQ 2006−2008 short-period temporary seismic stations. The epicentre distance varies from 75.1 degree for station PN41 to 78.2 degree for station PB04. Focal parameters and other description as in Fig. 4.

NON-REVIEWED CONTRIBUTION

Stud. Geophys. Geod., 52 (2008) 447

Grad M., Jensen S., Keller G.R., Guterch A., Thybo H., Janik T., Tiira T., Yliniemi J., Luosto U., Motuza G., Nasedkin V., Czuba W., Gaczyński E., Środa P., Miller K., Wilde-Piórko M., Komminaho K., Jacyna J. and Korabliova L., 2003. Crustal structure of the Trans-European Suture Zone region along POLONAISE’97 seismic profile P4. J. Geophys. Res., 108(B11), 2541−2565.

Gregersen S., Voss P. and TOR Working Group, 2002. Summary of project TOR: delineation of a stepwise, sharp, deep lithosphere transition across Germany-Denmark-Sweden. Tectonophysics, 360, 61−73.

Guterch A., Grad M., Keller R.G., POLONAISE’97, CELEBRATION 2000, ALP 2002 and SUDETES 2003 Working Groups, 2004. Huge contrast of the lithospheric structure revealed by new generation seismic experiments in Central Europe. Przegląd Geologiczny, 52(8/2), 753−760.

Majorowicz J.A., Čermák V., Šafanda J., Krzywiec P., Wróblewska M., Guterch A. and Grad M., 2003. Heat flow models across the Trans-European Suture Zone in the area of the POLONAISE'97 seismic experiment. Phys. Chem. Earth, 28, 375−391.

Fig. 6. Examples of vertical components of seismograms of a local event in the Lubin mine area recorded by PASSEQ 2006−2008 short-period and broad-band temporary seismic stations. Focal parameters from NEIC Catalogue: date 2006/10/14, time 7:41:08.0, latitude 51.40°N, longitude 15.96°E, depth 10 km, mb = 4.4. Time 0.0 refers to the origin time. All traces are normalized to maximum amplitudes and they are filtered with the pass Butterworth filter with 0.5 and 8 Hz corner frequencies.

NON-REVIEWED CONTRIBUTION

448 Stud. Geophys. Geod., 52 (2008)

Meier T., Malischewsky P.G. and Neunhöfer H., 1997. Reflection and transmission of surface waves at a vertical discontinuity and imaging of lateral heterogeneity using reflected fundamental Rayleigh waves. Bull. Seismol. Soc. Amer., 87, 1648−1661.

Pharaoh T.C., England R.W., Verniers J. and Żelaźniewicz A., 1997. Introduction: geological and geophysical studies in the Trans-European Suture Zone. Geol. Mag., 134, 585−590.

Schweitzer J., 1995. Blockage of regional seismic waves by the Teisseyre-Tornquist zone. Geophys. J. Int., 123, 260−276.

Świeczak M., Grad M., TOR and SVEKALAPKO Working Groups, 2004. Upper mantle seismic discontinuities topography variations beneath Eastern Europe. Acta Geophys. Pol., 52, 251−270.

Wilde-Piórko M., Grad M. and POLONAISE Working Group, 1999. Regional and teleseismic events recorded across the TESZ during POLONAISE’97. Tectonophysics, 314, 161−174.

Zielhuis A. and Nolet G., 1994. Shear-wave velocity in the upper mantle beneath central Europe. Geophys. J. Int., 117, 695−715.