A thorough review of the May 5, 1990 earthquake (southern Italy): constraints from macroseismology and insights from hydrology

Abstract. The May 5, 1990, Potenza earthquake (Mw 5.77) was a significant event for southern Italy, despite its moderate magnitude and limited damage. Previous macroseismic studies of this earthquake contained inconsistent and often exaggerated intensity values, particularly in areas far from the epicentre. Our analysis reveals that some overestimated intensities were caused by the overlapping damage patterns from previous earthquakes, due to the tendency to emphasize pre-existing or unrepaired damage, or attribute them to the most recent earthquake. In this respect, we re-evaluate all available data from original sources and compile a new and robust dataset comprising 1393 intensity values, assessed using both MCS and EMS-98 scales. This updated dataset shows a general decrease in higher intensity values compared to previous assessments, especially within 150 km of the epicentre. We also identify new data sources and remove unreliable entries. Recalculated macroseismic epicentres are in agreement with the instrumental estimate (i.e., 7.3 km using MCS data), while macroseismic magnitudes (Mw 5.05–5.19) are lower than the instrumental one. Additionally, we collect extensive observations of seismically-induced hydrological changes. These hydrological effects provide independent magnitude estimates ranging from M 4.9 to 5.7 for liquefaction and M 5.2 for streamflow responses. This comprehensive re-evaluation significantly enhances the accuracy and usefulness of the macroseismic and environmental data for future seismological research.