Summary:
The study area under investigation is Boeotia, located in Central Greece. This region is of considerable seismotectonic significance, as it lies between two active tectonic rifts: the Gulf of Corinth to the south and the Euboekos Gulf to the north. This setting has resulted in notable seismic events, both close and within Boeotia. Among the most well-known earthquakes from the historical era (pre-1900) is the Atalanti event of magnitude 7.0, which occurred on 27/04/1894, with its epicenter estimated to be north of Boeotia. Another significant seismic event of estimated magnitude 6.0 took place in the main town of Boeotia, Thiva, in 1914. Furthermore, the events of 24/02/1981, 25/02/1981 and 04/03/1981 with magnitudes Mw = 6.7, 6.4 and 6.4, respectively, are located close to the southern borders of Boeotia. Recently, four moderate events with magnitudes greater than 4.0 occurred close to Thiva: on 02/12/2020 (Mw = 4.6), 11/07/2021, 20/07/2021 (both Mw = 4.2) and 02/09/2021 (Mw = 4.1). It is imperative to conduct an up-to-date seismic hazard assessment for the Boeotia area, with the aim of reducing epistemic uncertainties. The assessment focused on quantifying the maximum anticipated ground motions through the computation of Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Spectral acceleration values (Sa). The Sa values were determined exclusively for the two major towns in Boeotia, Livadia and Thiva. Two methodologies were employed for the seismic hazard assessment: the classical semi-probabilistic approach and the scenario-based finite fault stochastic ground motion simulation. In the first approach, three seismotectonic models in the form of area sources were utilized, along with an updated earthquake catalogue. Multiple Ground Motion Prediction Equations (GMPEs) were applied to account for the main types of fault plane solutions based on their relative percentages. The results were derived through a logic tree approach and were visualized in the form of maps for PGA and PGV, considering return periods of 475 and 950 years, PGA-hazard curves for Livadia and Thiva, and Uniform Hazard Spectra (in terms of Sa) for Livadia and Thiva. Regarding the second approach, a calibration procedure was conducted prior to the stochastic simulations to ensure accurate incorporation of the source, path, and site parameters. Four earthquake scenarios were constructed to evaluate the modeled PGA, PGV, and Sa values. These scenarios included the 1894 Atalanti event with magnitude 7.0, the 1981 Alkyonides earthquake with magnitude 6.4, a simulation of an active zone rupture yielding an earthquake with magnitude 6.3, and the 1914 Thiva event with magnitude 6.0. Analyzing the results obtained via the probabilistic approach, it was observed that the central and northern portions of Boeotia generally comply with the PGA value proposed by the Greek Building Code, whereas the southern portion exceeds this value. Thiva exhibited higher levels of seismic hazard than Livadia across all return periods and demonstrated higher Sa values across all frequencies. Shifting focus to the second approach, only the scenario involving the Alkyonides earthquake generated ground motions that conform to the regulations outlined in the Greek Building Code. The Atalanti event posed a greater threat to Livadia, while the simulated rupture of the active zone of Kallithea – Mavrovouni with magnitude 6.3 poses a significant threat to Thiva.
Keywords:
Seismology, Engineering Seismology, Seismic Hazard, Probabilistic Seismic Hazard Assessment, Stochastic Seismic Hazard Assessment, Peak Ground Acceleration, Peak Ground Velocity, Peak Ground Spectral Acceleration, Return Period, Uniform Hazard Spectra, Boeotia, Thiva, Livadia, Central Greece
