Gianfranco Vannucci

A database of revised fault plane solutions for Italy and surrounding regions

The analysis of fault plane solutions of earthquakes is carried out in most seismotectonic studies to characterize the tectonic deformation styles and to estimate strain and stress directions in the investigated areas. Nevertheless the data available in the literature, are reported with different formats and notations and, in most cases, only in papery form, so that they are not suitable to be handled by computer procedures and graphic packages. Sometimes the data are reported with typographical errors, inaccuracies and inconsistencies that make them almost useless for other investigators. In some cases several solutions, often very different among each other, are given for the same earthquake by different authors thus requiring a choice be made among them. We have tried to solve some of these problems, in building a comprehensive database, on a Microsoft ACCESS platform, including most of the mechanisms (presently about 5000) published for the Italian region and more generally for the Mediterranean area. We tested 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. Moreover from the comparison of planes and axes we were able to detect and sometimes to correct misprints and other types of errors. All the parameters are recomputed uniformly and consistently, keeping track of all the corrections made. We also established an automatic procedure, based on several criteria, to choose the most “representative” solution when more than one is available for the same earthquake. The MS-ACCESS application also allows to making selections on the earthquake data, to display the plot of the mechanisms and to export data files suitable to be handled by graphic software and user written procedures.

FPSPACK: a package of FORTRAN subroutines to manage earthquake focal mechanism data

Earthquakes fault plane solutions (FPSs) are routinely computed on the basis of various techniques and are reported in the literature with a wide range of formats and conventions. Although the equations relating the various parameters are well known and relatively simple, their practical application often arise to numerical singularities and indeterminations that sometimes are not well known by the authors and thus may result in wrong or inaccurate reporting of parameters. Such inaccuracies and mistakes affect about 40% of the published data we have examined to test our programs. Moreover the current use, in the seismological community, of at least two different coordinate systems to represent the Cartesian components of vectorial and tensorial quantities is a further cause of confusion. In order to simplify the management of such data, we have prepared a structured package of FORTRAN 77 subroutines performing almost all of the possible computations and conversions among different parameters and coordinate systems. The package has been extensively tested with the data of a revised database of FPS of Italy and surrounding regions (presented in a companion paper) as well as of CMT solutions included in the Harvard catalog.

Encoding and computer analysis of macroseismic effects

Abstract We propose a method for the encoding and the computer analysis of the macroseismic effects deduced from historical sources allowing the complete formalization of the process of seismic intensity assessment. In the framework of historical sismology we make use of a multi-criteria decisions-support algorithm, based on the theory of the Fuzzy Sets. By analyzing the texts of the available sources for the 1919 Mugello and 1920 Garfagnana earthquakes, we followed a classification criterion which is independent of any macroseismic scale: we “disarrange” each sentence reported on the sources into 5 syntactic elementary components and represent it by a set of alphanumeric codes. This allows us to retain the maximum adherence to the original sources and to avoid forced interpretations and losses of information due to the need of fitting a given description to each observed effect. Moreover this scheme also allows to gather equivalent effects by reassigning them the same code, and to use this new classification in further processing. This procedure could even be seen as an attempt to define a new macroseismic scale on the basis of a statistical counting of different effects occurrences.