Geophysical study of deep basement structure of NW Poland using effective reflection coefficients

Abstract

The paper presents the possibility of applying the method of effective reflection coefficients (ERC) to recognise the deep basement structure for a case study of seismic profile GB1-III-86/89 from NW Poland. Two sectors of the seismic profile were selected in areas of occurrence of deep fractures bounding the Trans-European Suture Zone (TESZ) from the southwest and the northeast, respectively. At certain time intervals, due to transformation of the amplitude into an impulse form, seismic wave traces have been presented as effective reflection coefficients. An interpretation of the two sectors of profile GB1 provides a more detailed image of the complex geological structure of the Earth's crust in the southwestern and northeastern edges of the TESZ. The work has allowed for the identification of boundaries of reflection coefficients by distinguishing a number of layers and complexes (among others transition zones to the consolidated basement), and the determination of lines and seismic discontinuity zones, including the nature and location of the two deep tectonic fracture zones bounding the TESZ, as well as the Moho position. In particular, the southwestern sector of the profile shows cross-sections of two areas with different seismic structures, with a boundary that can be correlated with a deep fracture zone – the Trans-European Fault (TEF). The location and course of the boundary correlated with the Moho discontinuity is also defined. The northeastern sector of the profile, analysed at three time intervals, characterises the zone of deep fracture occurring in the northeastern part of the TESZ. Interpretation of the seismic section in its upper part illustrates seismic horizons that may define the Caledonian Deformation Front (CDF) and the northeastern limit of the Teisseyre–Tornquist Zone (TTZ), bounding the TESZ to the northeast. In the lower part, it represents the crustal structure and an attempt to identify areas of different structures: the lower laminated part and the upper homogenous part, as well as seismic discontinuity lines of tectonic and/or lithological origin. The applied method has delivered satisfactory results for the Lower Palaeozoic and older basement formations down to the Moho. The new form of seismic record, compared with the previously acquired wave image of profile GB1-III-86/89, significantly increases the possibility of interpretation and reliability of the results. The results confirm and justify the earlier concepts concerning the main tectonic features presented by researchers of this area. The experience and results justify the need for continuing the work using this method to verify and provide details about the extent of the structural-tectonic elements to the northwest and southeast, with reference to the research results from Poland and adjacent areas of Germany and the southern Baltic Sea.