On the magnitude and possible return period of the historical earthquake in ancient Savaria, 455 AD (Szombathely, West Hungary)

In 455 AD a strong, presumably M ≥ 6.0, earthquake occurred in or near the ancient town Savaria, the present Szombathely, West Hungary. According to the certainly incomplete earthquake catalogue, since then no similar significant seismic event occurred during the last 1500 years in this area which is currently considered inactive. Conclusions of this study are: (1) According to contemporary written historical sources (Annales Ravennates and biographical information about the life of Saint Severinus), the earthquake that destroyed Savaria and occurred in 455 AD had a magnitude of M ≥ 6.0. (2) In order to support the aforementioned magnitude value calculations were necessary. As the historical seismicity of the area is not known sufficiently an independent geodynamical approach – in parallel to the Gutenberg-Richter relationship – was used to estimate the return interval of earthquakes M ≥ 6. It was found in both cases that in the Szombathely region the recurrence time of earthquakes M6 and M6.5 is 1000 and 3000 years. Consequently, the earthquake activity of the Szombathely region is significantly lower than that of the Pannonian Basin in general.