Earthquake Mechanisms of the Mediterranean Area (EMMA) Database 3.0: First-Motion Focal Mechanisms and Their Ability to Characterize the Tectonic Deformation Style

We present a new version (3.0) of the database of Earthquake Mechanisms of the Mediterranean Area (EMMA) of "checked" first-motion focal solutions. The database, developed on MS-ACCESS, uniforms the different formats and notations of the data available in the literature and try to solve misprints, inaccuracies and inconsistencies that make them almost useless for other users (e.g. tests the perpendicularity of nodal planes and/or P and T axes of all solutions and, when both axes and planes are given, even their mutual consistency). An automatic procedure, based on several criteria, permits to choose the most "representative" (best) solution when more than one is available for the same earthquake. The database allows to make selections on the earthquake data and to export data files suitable to be handled by graphic software and user written procedures. For the Mediterranean region the first-motion focal mechanisms available from the literature allows to extend back in time, and to a lower magnitude threshold the data coverage of Centroid Moment Tensor (CMT) focal solutions of available Catalogs (Harvard University, Istituto Nazionale di Geofisica e Vulcanologia, Eidgenossische Technische Hochschule, Instituto Andaluz de Geofisica, USGS). With respect to the previous available version (2.1) we improve (+20%) the number of the data (about 7700 focal solutions at present), we add geographic information to the display of the focal solution plot, we permits to display the best solution and the other ones discarded (i.e. non-best). To solve some bias and inconsistence of the collected original data we also add to each mechanism the hypocentral parameters and the magnitude taken from the International Seismological Centre (ISC) Catalog. We verify the ability of EMMA database to characterize the tectonic deformation style, computing the cumulative moment tensor in the Mediterranean area on a regular grid with different seismogenic thickness, using the EMMA and CMT data separately. Then we use the rotational angle that should be applied to a cumulative focal mechanism to make it coincide with another one to verify the main differences between these patterns and the ability of EMMA database to reproduce the CMT Catalogs. To verify the quality of EMMA database we take advantage from some recent analyses that evidenced a relation between the Gutenberg- Richter b-value and the tectonic style of seismic release (in particular extensional mechanisms would correspond to higher b-values than compressive ones). We correlate the tectonic style as deduced from the cumulative moment tensor, previously detected, with the b-value computed by the ISC Catalog. We verify a good correlation between b-value and tectonic style using focal mechanisms taken from EMMA database