Combined geophysical techniques for detailed groundwater flow investigation in tectonically deformed fractured rocks

摘要

In this paper we present a combination of several near surface geophysical investigation techniques with high resolution remote sensing image interpretations, in order to define the groundwater flow paths and whether they can be affected by future seismic events. A seasonal spring (Amvrakia) located at the foot of Meteora pillars near the village of Kastraki (Greece) was chosen as a test site. The Meteora conglomeratic formations crop out throughout the study area and are characterized by large discontinuities caused by post Miocene till present tectonic deformation [Ferriere et al. 2011, Royden and Papanikolaou 2011]. A network of groundwater pathways has been developed above the impermeable marls underlying the conglomeratic strata. Our research aims to define these water pathways in order to investigate and understand the exact mechanism of the spring by mapping the exposed discontinuity network with classic field mapping and remote sensing image interpretation and define their underground continuity with the contribution of near surface geophysical techniques. Five Very Low Frequency (VLF) profiles were conducted with different directions around the spring aiming to detect possible conductive zones in the conglomeratic formations that the study area consists of. Moreover, two Electrical Resistivity Tomography (ERT) sections of a total length of 140m were carried out parallel to the VLF profiles for cross-checking and verifying the geophysical information. Both techniques revealed important conductive zones (<200 Ohm m) within the conglomerate strata, which we interpret as discontinuities filled with water supplying the spring, which are quite vulnerable to displacements as the hydraulic connections between them might be easily disturbed after a future seismic event.