The earthquake of September 9, 1998 in the frame of the historical seismicity of the Calabria-Basilicata border. Possible Seismotectonics Implication.

Abstract

We present the macroseismic data gathered after the September 9, 1999 earthquake (Io=6 MCS, Mercalli Cancani Sieherg scale, MI=5.5), which struck a wide area located between the Calabria and Basificata regions (southern Italy). The highest intensity datapoints distribution (HIDD) of 1998 has been compared with those related to the historical events of the area. It is worth noting that the regions located northward and southward of the area affected by the 1998 event are characterized by the occurrence of strong and destructive earthquakes (M ≥ 6.5), while the maximum historical intensity reached by this area does not exceed 8 MCS. On the basis of: 1) the HIDD of the historical earthquakes (new data has been provided for a local event of 1708) and of the 1998 one (which trends mainly E-W); 2) the instrumental parameters (depth close to 20-25 km and roughly E-W pure sinistral focal mechanism) and 3) the available data concerning the geodynamics context of the area (Gueguen et al., 1997; Patacca & Scandone, 1989), we hypothesize that the event can be related to a deep crustal shear zone, which is transversal to the chain and which is linked to differential eastward flexural retreat of the westward subducting Ionian crust.