Evaluations and processing of kinematic classifications for the integration of seismological and geological-structural data in active tectonic contexts

With the progress of geological and geophysical contributions to the study and description of the deformation of the Earth’s crust due to seismic events, scientists have developed numerous models of representation and kinematic analyses to assign a tectonic regime to the fault structures. Authors have attempted to develop classification criteria that reflect the actual rupture mechanism of the seismic source, using seismological data of focal mechanisms (Frohlich, 1992; Zoback, 1992) or the kinematic slip data of the fault (Aki & Richards, 1980). Most of these classifications suffer from several problems: 1) there are different classification criteria that can be applied to a data set, each of which gives its own result, often very different from each other, 2) the information obtainable from a focal mechanism (deformation axes and nodal planes) must be attributable to the same tectonic regime, 3) in the kinematic analysis it is important to consider not only pure “Andersonian” movements but also intermediate fields, 4) part of the focal mechanism data set is defined as “unknown”, thus subtracting information from the seismotectonic analysis. Based on these assumptions, we have developed a system capable of combining a type of classification based on geological data (slip vector rake) with a classification that takes into account seismological data (deformation axes P, T and B). In this work we analyze the quality and the problems related to the application of different methods of classification of focal mechanisms of an integrated seismic catalog of different authors. Through the creation of scripts in the MATLAB environment, the dataset was represented in ternary diagrams, useful for describing and schematizing the kinematic characteristics of a seismically active area. Then, on the same seismic database, different kinematic classifications were tested, using both the fault rake value and the orientation values of the deformation axes, in order to obtain the best relationship between the two different methodologies and to be able to assign to each mechanism the same kinematic regime. At the end of these tests, a classification by slip rake and a classification by deformation axes based on 10 kinematic fields are proposed, able to attribute the same results to 90% of the data used in terms of classification of the tectonic regime. These classification methods limit the gap on high quality data, integrating the geological data and seismological data present in the focal mechanism, and describe in more detail the deformation processes of the Earth’s crust related to fault structures and seismic sources. Finally, as an applied hypothesis of the work carried out, it was chosen to compare the Italian seismicity, discriminated on the basis of the classification proposed in the work, with seismotectonic zoning models from the literature, to highlight a good compatibility between the two data.