Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Displacement vector of continuous and repeated GPS measurements, and assessment of the present steady-state deformation across the Gulf of Corinth

The geodetic network deployed in the Gulf of Corinth is constituted by approximately 200 points: 50 1st order points, known with a 3mm horizontal accuracy for each survey, and about 150 2nd order points, known with a 1-2cm accuracy. The entire network covers a surface of about 100x80km, which corresponds, including sea surface, to 1 point every 5km. This dense network allows us to have a satisfactory sampling of the main active faults in the region.

Since 1990, eleven field surveys on this network were already organised. Two of them (1993 and October 1995) interested the whole 1st order network points, whereas in the other campaigns only a part of them was measured.

The last field survey in the Gulf of Corinth was organised in September 2001 in the framework of the CORSEIS project. The interest and aim of this survey was, first of all, to carry on with the monitoring of the deformation in the area, and, secondly, to detect the displacements occurred in the area in the last 11 years. During this survey, which spanned 12 days (from 18 to 29 September 2001), to ensure the maximum accuracy of the network and to have a certain redundance and repeatability, 33 1st order points of the 1991-1993 networks were observed three to four times. 19 among the 2nd order benchmarks were also observed for a single four-hours session.

The GPS data of all the surveys carried out in the region since 1990 were processed with GAMIT/GLOBK software (King & Bock, 1998; Herring, 1998). The velocity field obtained from the GPS data analysis indicates an almost N-S opening direction and puts in evidence two main features:

- Firstly, an important gradient of deformation localised offshore, on a very narrow band, in the central part of the Gulf of Corinth and quickly decreasing moving away through the interior.
- Secondly, an increase of the opening rate ranging between 11mm/year in its central part and 16mm/year to the west.

These rate values do not take into account the earthquakes contribution.

Horizontal co-seismic displacements observed for the Ms=6.2 June 15, 1995 event reach 15cm in correspondence of the northern coast and quickly decrease moving away towards the North. The southern block appears undeformed, except the region of Aigion event. This means that the accumulation rate of deformation on the major faults of the southern part of the Gulf is slow, lower than 1 to 2mm/year, but still difficult to estimate precisely. Such rate is compatible with long recurrence periods for large earthquakes (Ms=7) on these major faults of the southern Gulf of Corinth coast.

However, the area located immediately east of Patras, close to the Psathopyrgos fault, is discordant with the behaviour of the southern block (Peloponnisos) and it shows a deformation, which is concordant with the northern side of the Gulf.

Reported by

IPGP - L'Institut de physique du globe
4 Place Jussieu
75252 Paris
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