Ground Deformation Monitoring and Characterizing by Means of PSI, SBAS and DInSAR. Western Rift of Corinth, Greece
Elias, Panagiotis¹; Briole, Pierre^2
1National Observatory of Athens, GREECE; ²Ecole Normale Superieure, FRANCE

The rift of Corinth 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. It produces in average, an earthquake of magnitude 6 per century. 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 presents a major scientific and socio-economic importance, with the Psathopyrgos and the Rion-Patras faults being located very close to the city of Patras and have been selected for the study area.

The first DInSAR studies were carried out using SAR/ERS data after the Ms= 6.2 June 15, 1995 Aigion earthquake and contributed to its characterization.

More recently seismic and aseismic the ground deformations of the area have been measured using series of ASAR/ENVISAT, PALSAR/ALOS and RASARSAT-2 acquisitions. All datasets were processed by means of PSI, SBAS and DInSAR techniques. In addition to widely used tools (DIAPASON, ROI-PAC, STAMPS e.t.c.) in-house procedures and tools have been developed in order to exploit of the synergy of multiple characteristics/properties (frequency, viewing angles, sides etc) of the SAR acquisitions aiming to the minimisation of the noise components.

Two recent seismic events have been investigated by InSAR methodology.

On June 8th, 2008 an Mw=6.4 earthquake occurred in NW Peloponnesus, western Greece, at a distance of 17km SW of the city of Patras. This seismic event is the largest strike-slip earthquake that taken place in western Greece during the past 25 years. Although the magnitude was large enough to produce a land deformation detectable by DInSAR, no deformation was revealed, leading to the assumption that the focal depth exceeded the 20-25km.

On 18th of January 2010, an Mw=5.1 (NOA) earthquake occurred near Efpalion and 25 km NE of Patras. Another strong event occurred on 22nd of January 2010, with Mw= 5.1 (NOA) approximately 3 km NE of the first event. Intense post-seismic activity followed. Despite their low magnitudes those events show a small signature in C-band DInSAR. Modelling of the deformation source provided constraints on the location, size, azimuth and depth of the faults.

Aseismic deformation in the study area has been investigated.

We have exploited GPS measurements from permanent GPS network over the Gulf of Corinth to reference the ascending and descending ASAR/ENVISAT PSI deformation rate maps of the westernmost area of the Gulf of Corinth. Then we have calculated the Up-Down and East-West components from the referenced PSI maps. The results (profiles, maps etc) indicate many active structures which we characterized according to their type (fault or compaction zone) and the characteristics (deformation rate in Up-Down, East-West rates, azimuth etc) of its deformation source. Especially the Ag. Triada and Selianitika zones have been investigated for discrimination of their compaction due to the existence of old riverbed underneath and its deltaic depositions, respectively. Moreover data from PALSAR/ALOS and RADARSAT-2 has been used.

We demonstrate the agreement between GPS (those that haven't been used for reference) and PSI measurements, especially in the permanent stations of Trizonia, Psaromita and Lidoriki.

Our findings include the active zones inside the city of Patras (striking ENE-WSW, presenting aseismic surface slip rates ranging between ~1 - ~6 mm year-1 in the Up-Down component and ~1 - ~3 mm year-1 in the East-West component), the Rion-Patras (striking NE-SE, an oblique-slip transfer zone between the Corinth and Patras rifts, presenting aseismic surface slip rate of ~2 - ~4 mm year-1 in the Up-Down component and ~4 - ~6 mm year-1 in the East-West component) and the Psathopyrgos (striking E-W) fault zones. Moreover we have investigated the Aigion, Eliki, Pyrgaki, Lakka, and Nafpaktos fault zones. Part of Rio-Patra fault is passing through the University of Patras. Its position is very well constrained by the PSI data.

A discussion of the side products of the PSI processing will be performed. Issues as the tropospheric delay, detected landslides and observation ambiguities will be presented.