Moment magnitude–rupture area scaling and stress-drop variations for Earthquakes in the Mediterranean region

A dataset of moment magnitudes and rupture areas is compiled for 53 earthquakes that occurred in the Mediterranean region during the period 1976–2013. Moment magnitudes of these events range from 4.45 to 7.56, and the rupture areas are mainly inferred from the dimensions of their aftershocks zone. Three magnitude–area relationships that have been determined using global datasets, namely Wells and Coppersmith (1994), Hanks and Bakun (2002), and Shaw (2009), are examined to determine how well they fit these observations. The relationship of Shaw (2009) exhibits the best goodness of fit to the data, followed very closely by a modified version of the Hanks and Bakun bilinear relationship. Statistical tests show that the magnitude residuals of the two relationships are not significantly different, thus either of them could be used for seismic-hazard analysis. Stress drop of the selected events varies within a narrow range, increasing from 1 MPa for seismic moments less than 1 × 10¹⁸ N·m to about 6 MPa for larger events. Taking into account that the majority of the events under study are either normal or strike-slip earthquakes, this pattern of stress-drop variation is in contrast to that in areas like Taiwan or the Mexico subduction zone, where thrust faulting is dominant. For these areas, earthquakes tend to exhibit larger stress drops of up to 100 MPa, suggesting there is an apparent dependence of stress-drop variation on faulting type.