Harilaos Billiris

Geodetic estimate of seismic hazard in the Gulf of Korinthos

The recent 15 June 1995, M0 = 6.0 × 1018 N m, Aigion earthquake in the western Gulf of Korinthos has focussed attention on the seismic hazard of the region. Although there have been few large earthquakes in the region during this century, the historical record suggests that there may have been many large earthquakes there in the interval 1750–1900. We present geodetic data that give estimates of the rate of extension of the Gulf of Korinthos during this century and which suggest that less than half of the elastic strain in the central and western Gulf of Korinthos has been released by earthquakes during this century. In contrast, the seismic and geodetic strains in the eastern Gulf of Korinthos are in agreement with each other. If the discrepancy between seismic and geodetic strains in the western Gulf of Korinthos that has accumulated during this century is removed in earthquakes, the moment release will be equivalent to several Ms > 6.5 earthquakes.

Geodetic investigation of the 13 May 1995 Kozani‐Grevena (Greece) Earthquake

The Ms=6.6 13 May 1995 Kozani-Grevena earthquake struck a region of low historical seismic activity which includes a 10-year-old triangulation network in northern Greece. After the earthquake, monuments from this network were occupied with GPS to measure co-seismic displacements. Inversion of the co-seismic displacement field to yield a source mechanism is achieved by use of a hybrid simplex-Monte-Carlo method which requires no a priori constraints. The model focal mechanism agrees well with the global CMT solution and locally observed aftershocks, but implies a significantly higher scalar moment than do seismological or SAR interferometry studies, and has a longer fault length than the model based on SAR interferometry.

An Interdisciplinary Approach to Studying Seismic Hazard Throughout Greece.

This paper describes and reviews the progress of a three year (11/97–11/00) European Commission FP4 (Climate and Natural Hazards) funded project entitled GPS Seismic Hazard in Greece (SING), A major international interdisciplinary consortium is investigating and comparing strain derived using both geodetic and seismic methods.

GEODETIC MEASUREMENTS IN THE AEGEAN SEA REGION FOR THE DETECTION OFCRUSTAL DEFORMATION

Greece and the Aegean Sea form part of one of the most rapidly deforming parts of the Earths surface, and are characterized by a high level of intra-plate seismic activity in comparison to neighboring regions. AEGEANET is a geodetic network that we have established in order to measure consistently the geodetic strain in the broader Aegean Sea region, including parts of the Greek mainland and spanning several areas of known fault systems. Our measurements so far span approximately 4-, and 42-year periods up to 1997 using a combination of old triangulation/trilaterationderived coordinates and recent, repeated GPS observations at various subsets of the stations of this network. The observed displacements reflect the present day and long-term tectonic deformation of the region, showing more than one metre of northsouth extension across the network. The crust in this region appears to contain a few slowly deforming blocks separated by more rapidly deforming zones. This conclusion is supported by the velocity and strain fields that we have estimated for six sub-regions, which provide a more detailed view of the crustal deformation in this region.