Reappraisal of the 4 February 1867 Ionian Sea (Western Greece) earthquake and its impact on the environment, structures and public health

The 4 February 1867 earthquake is the largest in the Ionian Islands and one of the largest in the Eastern Mediterranean. However, it remained until recently one of the least studied historical events. In order to highlight its characteristics and impact we reevaluated existing knowledge and used new contemporary and modern sources.

The reevaluated sources included contemporary scientific reports and descriptions of local writers, while the newly utilized sources comprised contemporary local and national newspapers, additional reports from scientists and local writers, ecclesiastical chronicles, and modern sources such as scientific books, works by local authors, and local and national journals. The extracted information focused on: (i) the seismological parameters, (ii) the impact on the local population, (iii) the damage to buildings, and (iv) the earthquake environmental effects (EEEs).

The first category included the origin time and duration of the main shock, the epicenter location, precursors, and aftershocks, among other details. The impact on the population encompassed both the direct and indirect effects of the main shock, including the emergence of infectious diseases, as well as the demographic evolution in the following years. Regarding the building stock, the dominant building types were identified, along with the type, extent, and distribution of damage observed in villages and towns. The EEEs comprised ground cracks, landslides, liquefaction, hydrological anomalies, and sea disturbances, including a mild tsunami.

Based on the provided information, it is concluded that the affected residential areas were located within specific zones predominantly composed of post-alpine deposits and, to a lesser extent, alpine formations, both characterized by mechanical properties that render them susceptible to earthquake-triggered failures. Furthermore, the EEEs occurred in zones with high susceptibility to such phenomena, supported by a rich history of previous and subsequent occurrences. The available quantitative and qualitative data allowed for the application of the European Macroseismic Scale 1998 (EMS-98) and the Environmental Seismic Intensity Scale (ESI-07), facilitating a comparison of results and intensity distributions. This analysis highlighted the most affected fault blocks and identified the factors controlling their distribution.

This research has not only highlighted the benefits of utilizing such sources and information for reconstructing a historical destructive earthquake, but it has also demonstrated that independent sources remain to be explored and new perspectives could still provide valuable insights into historical earthquakes. Moreover, this study underscores that understanding the past seismicity of the Ionian Islands, as well as other seismically active regions worldwide, remains an open challenge for the global scientific community.