GPS constraints on current tectonics of Albania
Highlights
►First quantification of current displacements with GPS and CGPS in Albania. ►External area characterized by ongoing shortening and strike-slip faults. ►Internal Albanides are affected by southward displacements/to Apulia and Eurasia. ►Local gradients indicate N–S and E–W extension in internal Albanides.
Introduction
Current tectonics of Albania (Fig. 1) is characterized by microseismicity, small and medium size earthquakes and a few large events as shown by the occurrence of 6 earthquakes with Ms magnitudes exceeding 6 during the last century (Aliaj et al., 2004). The Ms > 6 earthquakes are: 1905, Shkoder earthquake Ms = 6.6, 1911 Ohrid lake earthquake Ms = 6.7, 1920 Tepelena Ms = 6.4, 1926 Durres earthquake Ms = 6.2, 1967 Diber earthquake Ms = 6.6 and 1979 Montenegro earthquake Ms = 6.9. Focal mechanisms (Louvari et al., 2001, Pondrelli et al., 2002, Pondrelli et al., 2004, Pondrelli et al., 2006, Pondrelli et al., 2007, Roumelioti et al., 2011, Sulstarova et al., 1980), as well as neotectonics investigations (Fig. 1) (Aliaj et al., 2000) underline the existence of a current E–W shortening across external Albanides whereas internal Albanides experience a multidirectional extension with directions varying from E–W to N–S extension (Carcaillet et al., 2009, Hoffmann et al., 2010, Tagari et al., 1993, Wagner et al., 2008).
Albanides (Fig. 1) are crossed by two transversal faults, the Vlora-Elbasani-Dibra fault zone and the Shkoder-Peja (also named Scutari-Pesh) one (Roure et al., 2004). This last fault zone is the northern boundary of the area including Albania and northern Greece. This Albanides–Hellenides domain is characterized by a NNW–SSE structural trend and by an important post Miocene rotation (Speranza et al., 1995, van Hinsbergen et al., 2005). North of the Shkoder-Peja or Shkoder‐Peja fault, Dinarides have not experienced such rotation and are characterized by NW–SE structural trends.
A few and sparse GPS velocities were available for Albania (Burchfiel et al., 2006) and the aim of our study is to quantify current deformation by means of a new dense continuous and episodic GPS network (Fig. 2) and to propose a geological interpretation of these results with the help of previous neotectonic investigations and focal mechanism data.
Section snippets
Data collection and processing
To quantify current velocities, we have installed since 2003 a network of five permanent GPS stations designed to investigate present-day velocity across the main active tectonic zones of Albania and a dense episodic GPS network (Fig. 2). This network of 32 points has been measured four times (Table 1),
Choice of a reference frame
To interpret GPS velocities in Albanides, we have decided to express velocities in the Eurasia fixed reference frame (Figs. 3a and 4a) and also in the reference frame corresponding to the plate subducted beneath the Albanides foreland, the Apulia microplate (Figs. 3b and 4b).
The segmentation of the Adria microplate in two parts: a northern one, the Adria block, and a southern one, the Apulia block formed by the Calabrian platform has been proposed by several authors (Babucci et al., 2004,
Existence of rigid blocks?
The discussion about the existence of rigid blocks limited by active faults characterized by their locking depth and by slips at depth is the subject of several studies concerning the current deformation of Greece (e.g. Floyd et al., 2010). For Albania, strain rate tensors allow to localize an area undergoing a very moderate deformation (P8, E12 and E19) in southern Albania. However the historical seismicity (Fig. 1) and the instrumental seismicity (Fig. 7), underlines a current deformation in
Conclusions
This study has allowed to characterize a complex current tectonics pattern in Albania: (1) the Shkoder-Peja fault is a major NE–SW transverse active faults that affects the whole collision belt and is the boundary between Dinarides and Albanides; (2) western Albania is affected by westward motions relative to Eurasia and Apulia microplate, the main part of this deformation is probably absorbed off shore along N–S to NNW–SSE active thrusts. Our results indicate the importance of transverse
Acknowledgments
The authors thank the NATO SFP 977993 and the Science for Peace NATO team to have supported this work. Most of figures were obtained by employing the GMT freeware package by Wessel and Smith (1998). The authors thank Anastasia Kiratzi and two anonymous reviewers for numerous and constructive suggestions.
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