Budowa głębokiego podłoża w Polsce na podstawie sejsmicznych badań refrakcyjnych

Stefan Młynarski

Abstract


 Po omówieniu zakresu wykonanych w Polsce badań refrakcyjnych scharakteryzowano metodykę pomiarów i zbiorcze interpretacje. Określono jakość uzyskanych wyników oraz powiązanie granic załamujących z utworami geologicznymi. Dokonano próby korelacji zarejestrowanych uskoków wzdłuż linii T-T, przeprowadzając ocenę obrazu sejsmicznego wzdłuż przekrojów. Skonstruowano mapę strukturalną granicy sejsmicznej refrakcyjnej o vg 5800–6500 m/s (fig. 5) związanej ze skałami prekambryjskimi podłoża krystalicznego lub ze skonsolidowanym podłożem nieokreślonego wieku. Przedstawiono również szkic strukturalny (fig. 6) dla granicy załamującej wiązanej z utworami podcechsztyńskimi.

 

THE STRUCTURE OF DEEP BASEMENT IN POLAND IN THE LIGHT OF REFRACTION SEISMIC SURVEYS

 

Intense refraction seismic surveys, carried out in the years 1965–1978, became the subject of numerous reports and papers. In 1974, J. Skorupa published seismic map of the country. New data coming from additional measurements and reinterpretations of earlier surveys make it desirable to summarize the present state of knowledge of deep geological structure in the country on the basis of refraction data.

The existing network of refraction seismic profiles does not display the state of knowledge as refraction boundaries are not traceable along a whole given section. This is partly due to differences in

measurement methods used in various periods. The deepest recorded refraction boundary is characterized by boundary velocity 5800–6500 m/s and low values of wave penetration coefficient, showing that we are dealing here with the record of front wave, related to strongly consolidated basement. In area of the Precambrian Platform, that boundary may be related to the top of Precambrian crystalline basement. Its record is broken at SW by a dislocation zone. The course of that zone is not always explicit, which may be due to SE–NW oriented translocations. The translocations are, however, difficult to establish on the basis of refraction data.

In the remaining part of the country (except for the area of the Fore-Sudetic Monocline which is out of scope of this paper), the deepest recorded refraction boundary may be only related to a basement treated as that of consolidated rocks. However, spatial interpretation is limited by the lack of a closed network of profiles for that boundary.

In a part of the Pomeranian Swell and adjoining basins, it is worth to note the record of “shallow” refraction boundary with boundary velocities ranging from 5500 to 5800 m/s. That boundary gives some data on sub-Zechstein rocks but rather general in character and fragmentary.

The state of knowledge of deep geological structure, based on refraction data, appears unsatisfactory.

This is because of discontinous record of interesting waves and, at the same time, difficulties in unequivocal identification of the studies refraction boundaries. Therefore, a special attention should be paid to the question of carrying out further refraction surveys.


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