Nups

NUPS: Acronym for NUcleation, Propagation and Stopping of the rupture. What is NUPS? NUPS is a package of FORTRAN codes to determine the source parameters of a circular crack propagating with variable rupture velocity. The rupture is modeled by assuming the model of Sato (1994) characterized by an initial linear growth of the rupture velocity (NUcleation phase) followed by a Propagation phase with constant rupture velocity and a linear decrease to zero of the rupture velocity (Stopping of the rupture). The theory is further described also in the article by Deichmann (1997). The inversion theory, based on the use of Empirical Green functions is instead described in de Lorenzo et al. (2008) for the first inversion step and in de Lorenzo & Michele (2024) for the second inversion step and the third step, based on the global exploration of the parameter space for the search for the optimal solution. NUPS is the result of a research effort that starts from the need to study the seismic source parameters of small magnitude earthquakes more accurately than is usually achievable with spectral inversion techniques based on generally very simplified models of the rupture process that essentially assume a constant rupture velocity. Even when more realistic rupture models are used (e.g. Boatwright, 1980), the mean rupture velocity is generally only approximately derived a posteriori through scaling laws. A constant rupture velocity is an unphysical assumption, which violates the causality of the rupture process. Furthermore, the modeling of P- and coda-waves in the time domain by such techniques remains a substantially unsolved or little addressed problem. EGF techniques in the spectral domain, which in recent years have been greatly improved and made definitively stable (Valleé, 2004), are generally able to reshape the waveform of the seismic signal radiated at the source very well for large earthquakes. For small earthquakes the EGF technique can be better formulated as an inverse problem in which the source model is assumed to be known and, furthermore, the deconvolution, which for signals of a few tenths of a second would be highly unstable, is replaced by convolution. NUPS is a code suite that tries to overcome some complex inversion problems. Since the inversion is performed in the time domain (in order to double the number of available data compared to spectral techniques), the most complex problem, from the point of view of the inversion procedure, consists in the relative shifting of the Main and EGF seismograms to find the optimal alignment of their respective arrival times P. This problem, which is already difficult to visually resolve in the case of signals affected by low noise levels due to the possible existence of a slow nucleation phase, becomes particularly dramatic in the case of noisy EGF and/or MAIN. In NUPS the codes have been optimized so that the different inversion steps corresponding to the possible different shifting points are performed in an iterative and automatic way. In this way the code suite allows to obtain the optimal solution through a series of 9 semi-automatic RUNS, which can be performed even by a novice student. NUPS has been in fact written with the aim of making its use as easy as possible for seismologists, and therefore to promote its widespread diffusion, convinced as we are that it offers enormous potential in the study of the source parameters of small earthquakes. The current version is only the first version, while with subsequent releases we will try to optimize somewhat primitive computer aspects of this package, since the author is not a computer scientist. OPERATING SYSTEM AND PROGRAMMING LANGUAGE The Fortran codes in the NUPS package must be compiled using the Linux operating system and gfortran for compilation. It is also necessary to have gnuplot if you want to use the utilities for the comparison graphs between observed and synthetic seismograms. NUPS is an open-source software that can be requested, for scientific purposes, by sending an email to: salvatore.delorenzo@uniba.it The inversion theory is described in the two articles cited above (de Lorenzo et al., 2008; de Lorenzo & Michele, 2024) that should be correctly cited by those who will use the code. To report code malfunctions or to request help in its operation, simply send an email to salvatore.delorenzo@uniba.it