Poster presented at the SAR Interferometry workshop at GEC-Marconi, Chelmsford, November 1995.
We are currently studying co-seismic and post-seismic strains in the regions of the large 1995 Grevena and Egion earthquakes, and the 1981 Alkyonides earthquake sequence, using a combination of GPS and conventional ground surveys.
These events are of body-wave magnitude range 5.9 - 6.5, resulting in horizontal ground displacements of up to 0.4m and vertical ground displacements of up to 0.2m for points within 20km of the fault break. These motions are capable of being easily detected using a combination of post-seismic GPS and pre-seismic trigonometric surveying. Okada's (1985) model of a finite rectangular fault in an elastic half-space can be used to determine the source parameters of the earthquakes, given geodetic surface displacements, but the inversion problem is highly non-linear.
Post-seismic relaxation of strain is expected to occur as the visco-elastic lower crust responds to co-seismic displacements. The model of Rundle (1978, 1982) predicts post-seismic displacements for these events of order 0.1m in horizontal and vertical components over a time-scale dependent primarily on the viscosity of the lower crust, and at present believed to be in the region of 5 - 20 years. A scheme of repeated GPS campaigns in the earthquake regions is currently being conducted by the University of Oxford in collaboration with NTU Athens and IPGP in order to test this and other models, and thus to determine geophysical parameters of the Earth's crust.