Abstract
GPS measurements recorded within the period from1992 to 2003 were employed to investigate horizontal tectonic stresses in the Earth's crust in the Baltic region. To avoid the impact of discrepancies in the systems of coordinates upon the parameters of deformations, the method of tensor analysis was applied thus estimating parameters employing the method of finite elements. Computations were performed using the created algorithms and applying ANSYS code. The values of tectonic stresses in the Earth's crust in the territory of the Baltic Sea region were calculated considering changes in maximum and minimum principal stresses. The value of change in maximum principal stress in the territory of the Baltic Sea region varies between –0.0013 MPa and +0.0032 MPa; the value of change in minimum principal stress varies between –0.0084 MPa and +0.0009 MPa. Positive values are dominating in directions of changes in maximum principal stresses (extension), whereas negative values – in directions of changes in minimum principal stresses (compression). Santrauka Žemės plutos horizontaliesiems tektoniniams įtempiams tirti naudoti 1992–2003 m. GPS matavimų duomenys. Siekiant išvengti koordinačių sistemų nesutapimo įtakos deformacijų parametrams, taikyta tenzorinės analizės metodika, parametrus įvertinant baigtinių elementų metodu. Skaičiavimai atlikti Ansysprograma. Apskaičiuoti Žemės plutos horizontalieji tektoniniai įtempiai Pabaltijo teritorijoje – svarbiausių maksimaliųjų ir minimaliųjų įtempių pokyčiai. Maksimaliųjų svarbiausių įtempių pokyčiai Pabaltijo teritorijoje svyruoja nuo –0,0013 MPa iki +0,0032 MPa; minimaliųjų – nuo –0,0084 MPa iki +0,0009 MPa. Резюме Для исследования горизонтальных тектонических напряжений земной коры были использованы результаты измерений ГПС, выполненных в 1992 и 2003 гг. Для того, чтобы исключить влияние несовпадения систем координат на полученные результаты параметров деформаций, была применена инвариантная системам координат методика тензорного анализа. Параметры деформаций вычислялись с использованием метода конечных элементов. Для моделирования использована программа Ansys. Определены тектонические горизонтальные напряжения земной коры в Прибалтике: главные напряжения. Максимальные напряжения находятся в пределах от –0,0013 МПа до+0,0032 МПа. Минимальные напряжения меняются от –0,0084 МПа до +0,0009 МПа.
Highlights
The objective of the present study is to evaluate the applicability of tensor analysis and finite element modelling approach dealing with horizontal stresses using geodetic measurements
Principal tectonic stresses are calculated as a quadratic equation (Atkočiūnas and Nagevičius 2004; Zaka revičius et al 2005): where v – Poisson’s ratio (0,25), εxz and εyz – relative shear strains, εzz – relative linear strain
The domination of extensional deformations in the western and northern parts of the Baltic region correlate with GPS data obtained from Fennsocandia that is accounted to the post-glacial up-doming of the lithosphere induced by glacial isostasy
Summary
Horizontal deformations of the Earth’s crust can be identified from changes in geodetic coordinates and other elements of the points of geodetic networks performing repeated geodetic measurements (Barba et al 2010; Dwivedi and Hayashi 2010; Ponraj et al 2010; Rontogianni 2010; Stanionis 2008; Zakarevičius 2003; Zakarevičius et al 2009, 2010a, 2010b; Zakarevičius and Stanionis 2007; Zhu and Shi 2011). Among the latest technologies for measuring a geodetic network, GPS is the most widely used approach. The repeated measurements of GPS networks enable a definition of horizontal stresses affected by the Earth’s crust. 24 geodetic sites were measured using 20 GPS receivers. The EUREF-POL2001 GPS campaign was carried out in September 2001 (Jaworski et al 2002). Five 24 hour-duration sessions were performed for the quality assurance of the Polish part of the EUREF-POL1992 campaign (Zielinski et al 1994). The 2003 GPS campaign under the framework of the Nordic Geodetic Commission (NKG) was carried out in GPS-week 1238 (28 September to 4 October 2003) (Jivall et al 2005a, 2005b, 2007). Processing the NKG GPS 2003 campaign was performed in four centres of analysis using three different software packages (Bernese version 4.2, version 5.0, Gamit/Globk, Gipsy/Oasis II). All coordinates were converted to the plane coordinates of Transverse Mercator projection (Table 1)
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