Baltic Sea Coast) Studied with Persistent Scatterers Interferometry
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Acta Geodyn. Geomater., Vol. 9, No. 1 (165), 19–29, 2012 NATURAL RECENT EARTH SURFACE DISPLACEMENTS OF SAMBIA PENINSULA (BALTIC SEA COAST) STUDIED WITH PERSISTENT SCATTERERS INTERFEROMETRY Zbigniew PERSKI 1)* and Marek MRÓZ 2) 1) Polish Geological Institute – National Research Institute, Carpathian Branch, Skrzatow 1, 31-560 Cracow – Poland 2) Department of Photogrammetry and Remote Sensing, University of Warmia and Mazury in Olsztyn, 1, Oczapowski Street, 10-718 Olsztyn – Poland *Corresponding author‘s e-mail: [email protected] (Received October 2011, accepted January 2012) ABSTRACT The paper describes the results of Persistent Scatterers Interferometry (PSI) study of Sambia peninsula. The idea of this work was to verify the hypothesis whether any terrain surface deformation that occur in Sambia area, could be interpreted as related to tectonic processes. Moreover, if any movements are detected what is their relationship to the 21 September 2004 earthquake? To answer these questions SAR (Synthetic Aperture Radar) data from European satellites ERS-1 and ERS-2 acquired from 1992 to 2001 were processed with interferometric techniques to archive independent data about terrain surface deformation. The obtained results – 4 sets of PS (Persistent Scatterers) points with calculated movement velocities (mm/yr) according to linear model were compared with published results of terrestrial measurements. The analysis of PS results confirms the occurrence of terrain deformations of tectonic origin of few mm/yr. The distribution of deformation velocities suggest its relationship to the recent activity occurring along two E-W trending seismoactive sub-zones located along Pregola river valley and possibly in the northern coast of Sambia Peninsula. KEYWORDS: SAR Interferometry, Persistent Scatterers Interferometry, seismoactive zones, Kaliningrad earthquake 1. INTRODUCTION – THE EXCEPTIONAL Husebye and Mantyniemi, 2005; Ulomov et al., KALININGRAD EARTHQUAKE 2008). Many local damages and deformations Sambia peninsula was considered as a seismical- associated with the earthquakes were recorded like ly quiet region and therefore the earthquakes occurred e.g. ground cracks, railway and riverbed collapses and on September 21, 2004 in the territory of Russian failures of the open pits edges due to landsliding, Kaliningrad enclave concerned big attention of small sinkholes. Good study of the local damages has seismologists and mass media. According to been given by Nikonov (Nikonov, 2011). The seismological records it was not a single event but two earthquakes caused minor damages to the buildings in quakes occurred on 11:05 UTC and 13:32 UTC Kaliningrad enclave and also in northern Poland followed by a fairly large aftershock recorded (Assinovskaya and Gorshkov, 2005; Gregersen et al., 4 minutes later (Gregersen et al., 2007). There were 2007; Nikonov, 2005, Nikonov et. al., 2006; Nikonov, several other small aftershocks that were felt, though 2010b). not recorded instrumentally. The magnitudes of the Due to exceptional character of Kaliningrad events were about 5.0 and 5.3, respectively, which earthquakes the authors decided to study a potential makes the two events one of the largest quakes noted earth surface deformations associated with the seismic in the 1000-year written history of the area (Nikonov event with spaceborne SAR (Synthetic Aperture et al., 2006; Nikonov, 2009, 2010a,b; Gregersen et al., Radar) interferometry. Unfortunately, due to lack of 2007; Wiejacz et al., 2006). However, such SAR data acquisitions of small temporal baseline – magnitudes could be classified according to global i.e. acquired just before and just after the earthquake Richter’s scale as moderate events; their macroseismic such “classical” study was impossible. However, evidences were very impressive. The two largest thanks to big data archive from European satellites quakes were widely felt in Kaliningrad enclave, ERS-1 and ERS-2 it becomes possible to check northern Poland, Lithuania, Estonia, Latvia and whether any measurable deformations in southern part Finland. Surface vibrations were felt also far away, in of Sambia peninsula could be detected during 8-years eastern Denmark, Belarus, Norway and in high-rise period prior to the earthquake. The presented paper is buildings in St. Petersburg (Gregersen et al., 2007; summarizing the results of that study. 20 Z. Perski and M. Mróz 2. GEOLOGY AND GEODYNAMICS OF SAMBIA Recent terrain deformations within Sambia area PENINSULA have been measured with leveling techniques and Kaliningrad region is located at the margin of the derived from sea level variations measured by East European Platform (EEP) and between two major mareograph stations in Svetlogorsk, Pioneer, Baltijsk Precambrian shields in Europe, i.e. Ukrainian Shield and Kaliningrad (Nikonov et al., 2009). According to and Baltic Shield. The basement of Sambia peninsula short term mareographs record Sambia peninsula is belongs to West Lithuanian Granulite domain uplifting from +1.1 mm/yr in the north to 3.9 mm/yr (Husebye and Mantyniemi, 2005) and is composed by in the south (Fig. 1). Unfortunately main part of the alternating belts of metamorphic rocks of amphibolite repeated leveling line was parallel to E-W direction and granulite phaces. The basement rocks are covered and therefore parallel to seismoactive zones. The by Paleo-Proterozoic sediments and young Quaternary velocities obtained by leveling show similar values to sediments. The sedimentary cover of Kaliningrad area mareograph data. However, several anomalies have is relatively thin, having 0.5 to 2.5 km total thickness been noted and described as the zones of contrast (Nikonov et al., 2009). movements (Nikonov et al., 2009). The locations of Neogeodynamically, according to the map of the anomalies agree very well with the general trace of vertical movements since the beginning of Rupelian southern seismoactive sub-zone. According to the stage (Ludwig, 2003), the Sambia peninsula remains values of recent movement velocities the Sambia stable. However, the authors of the map draw the peninsula is affected by gradual subsidence that faults bounding Sambia peninsula along the northern occurring westward and southwestward (Nikonov et and southern coasts (Fig. 1). These faults has been al., 2009). described as the Kaliningrad-Lithuanian potentially seismoactive zone by Aizberg at al. (1999). According 3. SEISMICITY OF SAMBIA AREA to these authors the zone is the western continuation The region of Sambia peninsula was considered of the large Kurzem-Polotsk faults zone and includes as not seismically active and no seismic processed three subzones: northern, central and southern. Within have been studied. Nikonov (2008) compiled the first the area of Sambia Peninsula central and southern catalogue of the earthquakes for this region paying subzones are located. Central subzone was described special attention to eliminate all events of as a small-amplitude rupture displacement associated anthropogenic origin and also non-tectonic frost with the regional active fault controlling the linear earthquakes (Nikonov, 2010a). According to this relief features. According to geological and author, over the period of 1990-2006 the seismic geophysical data the structure is present in the activity was increased in 1995 and 2004 with basement and cover sediments and it corresponds to tendency to southward spatial migration. a maximum magnitudes of Mmax = 4.0 with mini- The epicenter locations of 21 September 2004 mum depth to the earthquake focus H = 5 km. The earthquakes according to available instrumental data southern subzone consists of two latitudinal faults also have been calculated by different authors. All these determined from geological and geophysical data. The estimates differ significantly since the nearest seismic considered faults are situated in a zone of rather strong station was located in Suwałki in Poland, some neotectonic deformations and therefore the subzone 220 km away. Early estimates presented by Wiejacz was classified as active with corresponding values of (2004) suggest that the epicenters of both main shocks Mmax = 4.0; H = 5 km (Aizberg et al., 1999). were located offshore, close to southwestern coast The main neogeodynamical feature of northern near Baltijsk town. According to Nikonov (2006) the Europe is the postglacial uplift in Fennoscandia. epicenters of two main shocks were located at the sea Sambia peninsula and southern Baltic coast are bottom, but close to northern and western coast of located in its marginal zone where vertical Sambia. Epicenters calculated by Husebye and deformations are close to zero. A good review of this Mantyniemi (2005) are locating the earthquake close neotectonic feature was given by (Fjeldskaar et al., to the center of the peninsula. Good reviews of 2000). According to the model presented by different epicenter locations was given by Gregersen Gudmundsson (1999) the marginal zones of et al. (2007) and Aleshin et al. (2007, 2009). All postglacial uplift are affected by compressional stress analysis emphasizing that instrumental data and fields and therefore strike-slip and reverse faulting macroseismic fields are significantly diverges. may occur. Similar conception was derived by According to macroseismic observations Gründhal (2003) who analyzed directions of recent (Assinovskaya and Ovsov, 2008) which are more maximal stress of Central Europe. The Kaliningrad consistent than instrumental data, the highest intensity area, Baltic countries