New insights on subsurface geological and tectonic structure of the Athens basin (Greece), derived from urban gravity measurements

Abstract

The gravity method has been applied, with a total of 1.122 gravity measurements for the subsurface investigation of the geotectonic structure beneath the urban and sub-urban areas of Athens basin. The aim was to either verify previously mapped concealed fault zones or even discover new concealed faults that may affect the city in the future by generating disastrous earthquakes. Three different methods have been used to determine the densities of the existing geological formations in the best possible way: laboratory measurements, Nettleton profiles and the seismic velocity conversion. In the context of the qualitative interpretation, we took advantage of the derivatives methods in order to enhance the structural edges of density sources that may reflect fault zones. Thereby, several structural maps have been produced by applying most of the enhancement techniques, such as the Total Horizontal Derivative (THDR), the First Vertical Derivative (VDR), the Second Vertical Derivative (SVDR), the Analytical Signal (AS), Tilt (Tilt) and the Theta (cos Tilt). Their results were extremely helpful, providing severe indications for the delineation of the fault pattern of the area. These results were combined with interpretive geological 2.75-D density models in order to verify or modify fault regime of the area. Important data regarding the geological and tectonic structure beneath the Quaternary formations were retrieved. More specifically, we were able to verify and modify the locations and lengths of already proposed as concealed faults zones from older geological researches or even better to identify and propose new locations of concealed faults that have not been identified so far.