Supervisors info:
Γεώργιος Καβύρης, Αναπληρωτής Καθηγητής, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Summary:
The Gulf of Corinth is a natural laboratory for conducting seismological studies. The occurrence of strong and destructive earthquakes since antiquity contributes significantly to shaping the local cultural and financial human activity. Seismicity in the Western Gulf of Corinth has been the focus of several studies. In the region, tectonic structures predominantly strike WNW-ESE, followed by a NE-SW extension. Thus, the Gulf of Corinth has the characteristics of a graben. Dense seismological networks have been deployed in the area for decades, to monitor the wealth of seismic events. Local stations of both the Hellenic Unified Seismic Network (HUSN) and the Corinth Rift Laboratory Network (CRLN) are commonly used in seismological studies. On 30/03/2019, a strong ML=5.2 earthquake struck the area, being felt by the local population. Such an event is not common the Gulf of Corinth, where seismicity is mainly expressed with swarms.
Shear-wave splitting is a valuable tool in determining the state of accumulated stresses in a rock volume. It has been linked to a preparatory period of activity that precedes a strong shock, as it can represent processes of stress accumulation and relaxation. Shear-wave splitting can monitor changes of fluid-filled microcracks in the upper crust, relating to their geometry and density. Such studies are being conducted by examining the angle of polarization of the fast shear-wave and the time-delay of the arrival of the slow shear-wave.
During the current study, recordings from five local stations of HUSN (EFP, KALE) and CLRN (AGRP, MG00, ZIRI) were analyzed for shear-wave splitting. A shear-wave window of 45⁰ was applied to avoid contamination from secondary phases.
A total of 123 pairs of splitting parameters were determined. The average polarization directions follow the faults and tectonic structures of the gulf and, by extension, the maximum horizontal compressive stress component, insinuating the application of the Anisotropic Poro-Elasticity (APE) model. Moreover, 3-month long steady increase of normalized time-delays was observed before the occurrence of the 30/03/2019 ML=5.2 event.
Keywords:
SEISMOLOGY, SEISMIC ANISOTROPY, SHEAR-WAVE SPLITTING, GULF OF CORINTH
