PALAEOSEISMOLOGY - REVIEW OF THE STATE-OF-THE-ART

Historical seismicity provides only a partial indication of the seismotectonic character (i.e. earthquake potential) of a given region. Even in Italy, where a relatively long historical record exists, available catalogues are generally unsatisfactory for this purpose. Fortunately, strong earthquakes often leave geological evidence, herein referred to as seismites, that are mainly related to surface faulting, folding or other deformation, and occasionally to secondary ground failures (e.g. landslides, liquefaction features, etc.). These features may be preserved and, therefore, palaeoseismological studies may detect and date them, thereby permitting extension of knowledge beyond the local historical threshold (up to 2000 years in the most fortunate cases). This paper provides a summary of criteria which may aid in the identification of areas suitable for palaeo-earthquake investigation. Historical seismicity and the presence of well developed tectonic geomorphic features are recognized as the most reliable criteria for identifying active faulting. However, lack of these characteristics cannot be considered conclusive evidence for lack of activity. Palaeoseismological techniques aim at identifying not only the obvious effects of surface faulting, such as offset of young geologic units, but also the more subtle tectonic or non-tectonic features, including liquefaction structures, gravity features and coseismic uplift and/or subsidence. Finally, we discuss some questions that pertain to palaeoseismicity evaluation techniques. Among these are the reliability of the Quaternary dating techniques, the evaluation of the seismic energy released (minimum magnitude) and principally, the unequivocal identification of a seismic origin for the considered geological structures.