A ten years analysis of deformation in the Corinthian Gulf via GPS and SAR Interferometry

Abstract

The Corinthian Gulf in Greece, is the most active of a series of extending grabens which accomodate the deformation in the highly seismic Aegean region. The geodetic network established in the region has about 200 points: 50 1st order points and ~150 2nd order points. The network covers an area of about 100 x 80 km2, which correspond to an average density of 1 point every 5 km2. This dense network allows to study the main active faults in the region. Eleven field surveys were organized in 1990, 1991, 1992, 1993, 1994, June 1995, October 1995, 1997, and 2001. Two earthquakes occurred in the vicinity during the ten years period: the 1992, 18 November Ms=5.9 Galaxidi earthquake and the 1995, 15 June 1995 Ms=6.2 Aigion one. With respect to the stable Europe, we find for Peloponnessos an average displacement rate of 30 mm/yr in the N215° direction, similar to that found in previous studies. Our results show that most of the deformation in the Corinthian Gulf is localizes off-shore, in a narrow band, in the central part of the Gulf. The extension rate measured over 10 years is 11 mm/yr in the N185° direction in the middle of the Gulf (Xiloxastro) and 16 mm/yr in the N185° direction in its western part (Aigion). The southern block appears un-deformed, except the region of Aigion event. Using CNES DIAPASON software, we derived 85 interferograms of the Corinthian Gulf from 38 raw ERS SAR images acquired between 1992 and 1999. The interferograms sampling the 1995 earthquake show a clear coseismic signal reaching 250 +/- 15 mm at Psaromita cape, a value consistent with the GPS measurements. No post-seismic motion, within the error bars of SAR interferometry (+/- 15 mm), is observed during the 1995-1999 period.