Ground deformation observed in the western Corinth rift (Greece) by means of SAR interferometry
The rift of Corinth (Greece) has been long identified as a site of major importance in Europe due to its intense tectonic activity. It is one of the world’s most rapidly extending continental regions and it has one of the highest seismicity rates in the Euro-Mediterranean region. The GPS studies conducted since 1990 indicate a north–south extension rate across the rift of ~1.5 cm year-1 around its western termination. Geological evidences show that the south coast of the rift is uplifting whereas the north part is subsiding. The western termination of the rift in the Patras broader area, with many active faults lying very close and inside the city of Patras, presents major scientific and socio-economic importance. Recent seismicity has affected this end of the rift with the Movri (Achaia) earthquake in june 2008 and a seismic swarm around Efpalio (Fokida) in January 2010. Additionally the presence of a plurality of geophysical phenomena and morphological features renders this area and the Gulf of Corinth generally, as natural laboratory, a place of international initiatives as the Corinth Rift Laboratory and a case study for the EO Supersites initiative. Seismic and geodetic ground measurements from permanent networks (since 2000) and measuring campaigns (since 1990) have been (and are) performed. Moreover dense SAR data are available since 1992 and the ERS1 mission. Motivated by the lack of precise and extended mapping of the vertical deformation of the area and by the limitations of the GPS network (in terms of density of points) we investigate, model and interpret a large set of SAR interferometry data completed by the GPS data. The SAR interferometry data are very powerful for measuring vertical motions, for mapping localized deformations across faults or other features and for mapping and modeling the co-seismic deformation produced by earthquakes. We processed ascending and ascending acquisitions of ASAR/ENVISAT in the period between 2002-2010, to produce Persistent Scatterrers and Small Baseline Subsets deformation rates maps. These products have been combined together but also constrained with a number of GPS observations in order to extract the precise Up-Down and East-West deformation components field. The methodology chain performed globally well over the area (despite the vegetation cover and slopes) and provides accurate and robust results in many areas. We verified the agreement between GPS and the InSAR deformation field rates. We also compared them with remote sensing and ground observations of independent studies. We focused in specific case studies and presented the deformation rates along cross sections inside the city of Patras, around the Rion-Antirion bridge, around the urban areas of Psathopyrgos, Aigion, Sellianitika, Nafpaktos, Ακratas, the island of Trizonia, and the river deltas of Psathopyrgos, Sellianitika, Aigion, Mornos, Marathias and Akrata. Significant ground deformation is observed within the city of Patras itself, due not only to urban subsidence often seen elsewhere, but also to the motion of shallow structures likely to be induced by deep tectonic movements at the junction of the right lateral strike-slip fault linked to the Movri and penetrating inland between Rio and Patras (trans-tensional fault of Rio Patras), and the Psathopirgos normal fault at the entrance of the Corinth Rift. The Rio-Patras fault is a transition, oblique, structure, connecting the strike-slip zone to the south and the extentional area to the east. The Aigion fault appears very active with uplift rate of about 2mm/an, the highest rate across the Corinth Rift in the sample period, this uprising damping in the three kilometers separating this fault from the West Helike fault to the south. The observed discontinuities of the deformation field are not always correlated with seismic activity at the same place in the sampled period. The Temeni-Valimitika delta, east of Aigion, is the only delta of the area not subsiding (at least at its bigger part). We think that this is because it is located on the footwall of the Aigion fault with the delta compaction/subsidence balanced by the tectonic uplift. All the other deltas are subsiding due to the compaction of their sediments, and in the big ones it is possible to observe a linear increasing rate as approaching their coastal borders. The 2008 and 2010 seismic events occurred in the study area are modeled by inversion of their sources parameters using a model of dislocation in an homogenous elastic half-space constrained by the seismic, the GPS and the SAR interferometry data. At the broad scale, most of our studied tectonic features are pieces of a (diffuse) triple junction between micro-plates at the boundary between the rift of Corinth to the east and the termination of the Hellenic arc to the west. We briefly investigated and discuss the Trikonida and Aitoliko valley deformation field in the northwest of the triple junction area. Finally for the sake of completeness and in order to assess the capabilities of the space geodesy we presented some inferred discontinuities occurred by landslides and some by unclear origin and requiring further investigations.
Faults, Earthquakes, Gulf of Corinth, Ground deformations, Space geodesy, Remote sensing, 551.872, Ρήγματα, Σεισμοί, Κορινθιακός κόλπος, Εδαφικές παραμορφώσεις, Διαστημική γεωδαισία, Τηλεπισκόπηση
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