Μελέτη των περιβαλλοντικών συνθηκών έκλυσης του χημικού στοιχείου 222Rn και η πιθανή συσχέτιση της με τη σεισμικότητα της περιοχής Μεγάρων

Abstract

Over the last decades evidence for correlation between radon emission and earthquake activity suggests that monitoring of radon in soil gas can be used as a method to predict future earthquakes. However, although the method is promising for earthquake prediction and most of the seismic activity in Europe is released in Greece, no systematic experiments were conducted so far. In this study we present preliminary results of a two years experiment through the monitoring of eight sites in the Megara basin. In each site, soil radon exhalation was monitored in shallow boreholes (80 cm deep), using CR39 films, which were exposed every 15-day. The Megara basin was selected as a study area for the following reasons: (a) the basin is actively deformed and most of this deformation is accommodated by strong historic earthquakes. The most recent of these events are the 1981 Corinth earthquake sequence. (b) Within the basin large faults have spectacular outcrops, and or still preserve seismic ruptures. Thus the tectonic setting of the monitoring sites is well known in its tectonic position. (c) The entire experiment is set up quite close to Athens, thus earthquake epicenters are calculated fairly well and detailed meteorological data are also available. The experiment includes a series of monitoring sites distributed from Megara town to the coast of the Alkyonides bay, that it well known as the epicenter of the 1981 Corinth earthquakes. In essence the coastal area of the Gulf is rather the surface expression of the South Alkyonides Fault zone. Surface displacement along this fault during the 1981 event reached up to 1 m north side down. Based on these monitoring sites, we present the first results regarding the background soil radon concentration in the Megara basin as well as radon exhalation through a fault. Specifically, we present data of radon exhalation through a still preserved co-seismic rupture, 20 north of the rupture on the hanging wall block and 200 m south of the rupture within the footwall block of the South Alkyonides Fault zone.