Analysis of a geodetic network using products of Legendre and Hermite polynomials for detecting real crustal movements

SUMMARY Just after the big earthquake which occurred in the Thessaloniki area on 1978 June 20, a 16-point trigonometric network was installed in the epicentre area between lakes Lagada and Volvi at a distance of about 30 km from Thessaloniki. This network has been measured on five successive surveys in 1979, 1980, 1981, 1982, and 1983. We used the already available triangulation results of these five surveys in order to derive conclusions concerning the relative positions of the network stations. This was performed by using an analytical method which allows us to split up the observational data into a systematic part and a random part and with development of the systematic part into a series of an appropriate system of functions using Legendre and Hermite polynomials. The systematic displacement vectors found, show a trend towards the centre of the area. With the advance of time, this trend changed to a rotation of the field around this centre.