Magnitude distribution of linear morphogenic earthquakes in the Mediterranean Region: insights from palaeoseismological and historical data

We analyse the earthquake magnitude distribution of 'linear morphogenic earthquakes' that reactivated dip-slip normal faults within the Mediterranean Region. Information on past events is obtained following two distinct methodological approaches: the geological one (morphotectonic investigations and palaeoseismological excavations) and the historical one (contemporaneous descriptions and surveys of coseismic ruptures). In order to homogenize the different datasets, and therefore enabling a comparison, we calculate moment magnitudes (Mw) starting from seismic moments (M0) estimates. The cumulative distributions thus obtained for the two datasets show differences that a series of non-parametric tests suggests to be statistically significant. Coseismic displacements are systematically overestimated for strong (Mw>6.5) historically-based earthquakes and for moderate (5.0-6.0) palaeoseismologically-observed events. Also concerning the rupture length, the geological information generally provides larger values for moderate earthquakes. The possible causes of this discrepancy and the consequences in using the two datasets for seismic hazard assessment analyses are also discussed.