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SUMMARY Two passive seismic experiments have been carried out across the Trans European Suture Zone (TESZ) from northern Germany to southern Sweden (TOR) and across the ProterozoicArchaean suture in Finland (SVEKALAPKO) to improve our understanding of the processes involved in the creation of the European continent. Teleseismic earthquakes recorded by the two networks and stations of the GRSN and GEOFON permanent networks have been used for studies of the crust‐mantle, and upper mantle seismic discontinuities with the receiver function method. Along the TOR network the depth to the Moho increases from 30 km at the southern edge of the profile to 40 km at the Elbe Line. Between the Elbe Line and TESZ the Moho branches off and whereas the deeper branch continues at 40 km depth to the TESZ a second branch appears at 30‐35 km depth. The upper branch descends north of the TESZ to below 55 km under the northern end of the TOR profile. The crustal thickening north of the TESZ is accompanied by an increase in average Vp/Vs values, appearance of intracrustal conversion zones and north dipping features which we interpret as remnants of the subduction and subsequent collision between Avalonia and Baltica. In southern Finland beneath the SVEKALAPKO network the Moho starts in the south at the depth of 40‐45 km, plunges to about 65 km depth south of the Archaean-Proterozoic suture. This deepening of the Moho is coincident with a north dipping intracrustal structure apparently related to the subduction and collision and of the Proterozoic and Archaean provinces in Proterozoic. North of the line of the suture the Moho rises smoothly to 45‐50 km depth in the Archaean province. Along the TOR profile, 410 and 660 discontinuities were hard to detect. However, manyfold stacking of receiver functions revealed that the conversions from the two discontinuities arrive more or less according to IASP91 predicted time. Across the SVEKALAPKO network 410 and 660 discontinuities arrive markedly earlier than IASP91 theoretical arrival times. In particular north of the Archaean-Proterozoic suture in Finland the 410 and 660 km conversions arrive about 2 s earlier, indicating about 5 per cent higher average upper mantle velocities and lower temperatures than what IASP91 global model predicts.

The structure of the mantle transition zone between two seismic discon-tinuities at depths near 410 and 660 km is one of the most important issues to understand the Earth’s dynamics. Most of what we know about this zone is based on seismic interpretation. Seismic waves observed in the distance range of about 15-28° turn in the transition zone and give us information about structural details of penetrated region. We present new results on the upper mantle velocity struc-ture beneath Eastern Europe obtained from individual earthquakes for which seismic data has been collected during two passive experiments, TOR and SVEKALAPKO. Comparison with the earlier models describing the upper mantle velocity structure allowed to study lateral changes in the topography of the 410 and 660 discontinuities. Variations in the average thickness of the transition re-gion are thought to reflect variations in the mantle temperature. We cannot ex-clude non-thermal effects occurring in the Earth’s mantle but the thickness of the transition zone may be a useful thermometer for indication of lateral temperature variations. The size of velocity jumps could be translated into chemical composi-tion, mainly for olivine content at discontinuity.

The TOR project investigates the lithosphere–asthenosphere structure under the Tornquist Zone between Denmark and Sweden. Around 150 seismic stations (108 short-period, 28 broadband and 14 other permanent stations) were employed in a rectangular array along a 900 km long by 100 km wide strip across the Tornquist Zone from July 1996 to August 1997. The results obtained based on a non-linear teleseismic tomography algorithm reveal significant P-velocity variations (up to 5 per cent) along the TOR array from northern Germany to southern Sweden. Distinct lithospheric blocks are also recognized in the inversion results. Two inverse methods (singular value decomposition and a quadratic programming method) were implemented in order to investigate whether or not the lithospheric blocks and major boundaries in the inversion are required by the data or are artefacts of the inversion. According to the results, the lithosphere under northern Germany is thin but reaches to intermediate thicknesses of about 120 km in the Tornquist Zone area. Farther north in the Baltic Shield, more than 200 km of continental lithosphere is recognized in the model. Abrupt lateral P-velocity changes (maximum 5 per cent) are seen at both the southern and northern sides of the Tornquist Zone.

During the TOR-1 passive seismic experiment in 1996/97, a maximum of 139 temporary seismograph stations were operating over the Sorgenfrei-Tornquist Zone (STZ) in an area extending from northern Germany through Denmark to central Sweden. One of the objectives was to study horizontal anisotropy directions in the subcrustal lithosphere and asthenosphere across the Trans-European Suture Zone. To achieve this goal,broad-band and intermediate-period (5 s) data of the TOR-1 stations and additional stations of permanent networks (GRSN, GEOFON) were analysed for splitting of SKS and SKKS phases. As a result of the relatively dense station spacing, the method offers good lateral resolution of anisotropy.Preliminary results suggest that the directions of the fast horizontal S wave velocity are affected by the STZ. In central Europe and southern Sweden, far away from the STZ, fast S wave directions are approximately E-W while they turn more northerly closer to the STZ where they are approximately parallel to the trend of the STZ. No significant shear wave splitting was observed north of 57 degr. N and east of 14 degr. E. Small delay times between 0.2 and 0.5 s observed at the northernmost TOR-1 station T40S and T60S may be controlled by anisotropy in a thickened crust. The mantle contribution of horizontal anisotropy within the STZ is probably constrained to an approximately 60-km-thick zone in the depth range between 70 and 300 km. The observations are consistent with a model where azimuthally anisotropy is not governed by present-day mantle flow in the asthenosphere, but rather is frozen into the subcrustal lithosphere during the last episode of tectonic activity.