Supervisors info:
Ιωάννης Αλεξόπουλος, Αναπλ. Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, ΕΚΠΑ
Summary:
This thesis, with title “Investigation of the physical characteristics of the lithologies of the city of the island of Corfu with the application of geophysical exploration methods”, aims to apply geophysical methodologies to investigate the physical characteristics of the geological formations that structure the urban area of the city of Corfu. The objective was to classify the formations in the area based on its geotechnical characteristics.
The city of Corfu consists at its base of limestones of the Ionian unit, namely the Pantokrator limestones and the Vigla limestones. On top of the limestones, have been deposited during the Miocene the basal conglomerates and the metatectonic unit continues with marls until the upper Miocene.
The geophysical work was carried out in 10 locations within the urban area of Corfu town, in surface outcrops of the different geological formations and in locations that met the requirements for the application of the field methodologies. The first geophysical method applied is the geoelectric method, specifically the electrical resistivity tomography technique (ERT). In the same locations, the seismic method was applied. In particular, the seismic refraction technique (SRT) and the multi-channel analysis of surface waves (MASW) method were applied.
Sampling of the geological formations that structure the city of Corfu was carried out to determine their density in the laboratory and in combination with the seismic wave propagation velocities the elastic constants of the lithologies were determined.
From the processing of the geoelectric data the resistivity of the marls ranges from 30 to 40 Ohm.m, of the Miocene conglomerates from 400 to 500 Ohm.m, of the Vigla limestones from 400 to 700 Ohm.m and of the Pantokrator limestones from 300 to 400 Ohm. m. From the processing of the seismic data, the primary wave propagation velocity in the marls was determined to be 1300 m/s, in the Miocene conglomerates 2350 m/s, in the Vigla limestones 2400 m/s and in the Pantokrator limestones 2500 m/s.
The Vs30 index was calculated for the marls in 380 m/s, for the conglomerates in 960 m/s, for the Vigla limestones in 980 m/s and for the Pantokrator limestones in 970 m/s. Based on the calculation of the Vs30 index, the geological formations of Corfu town were classified according to the European regulation Eurocode 8.
Finally, distribution maps of the seismic wave propagation velocities Vp and Vs, the Vs30 index, the elastic constants (σ, E, λ, μ) and the mechanical parameters of the surface layers (Ci, V, Di, Si) were constructed. Both elastic and mechanical parameters of the surface layers in the northern part of the old town of Corfu correspond to more compact rocks of the Ionian geological unit, while in the southern part of the town they correspond to less cohesive rocks corresponding to the Miocene metatectonic sequence.
Keywords:
City of Corfu, Geophysical Exploration, Resistivity Method, ERT, Seismic Method, SRT, MASW, elastic properties, mechanical parameters, classification of ground types
