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

Abstract

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.