Showing papers by "Vito Latora published in 1998"

Lyapunov Instability and Finite Size Effects in a System with Long-Range Forces

Abstract: We study the largest Lyapunov exponent $\ensuremath{\lambda}$ and the finite size effects of a system of $N$ fully coupled classical particles, which shows a second order phase transition. Slightly below the critical energy density ${U}_{c}$, $\ensuremath{\lambda}$ shows a peak which persists for very large $N$ values $(N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}20000)$. We show, both numerically and analytically, that chaoticity is strongly related to kinetic energy fluctuations. In the limit of small energy, $\ensuremath{\lambda}$ goes to zero with an $N$-independent power law: $\ensuremath{\lambda}\ensuremath{\sim}\sqrt{U}$. In the continuum limit the system is integrable in the whole high temperature phase. More precisely, the behavior $\ensuremath{\lambda}\ensuremath{\sim}{N}^{\ensuremath{-}1/3}$ is found numerically for $Ug{U}_{c}$ and justified on the basis of a random matrix approximation.

Time Correlation Analysis of the Microseismicity of the Low Eastern Flank of Mt. Etna Volcano (Italy)

Abstract: —An analysis in terms of time correlation functions has been applied to the time distribution of microseismicity. We considered the single station detections (M < 2) recorded by each one of the four working stations of the network of the Osservatorio Sismologico di Protezione Civile, Acireale (Catania), located on the active faults systems (Timpe) of the low eastern flank of Mt. Etna. Information obtained on the time regularity of seismic crisis and on the time correlation between the activities recorded by different stations allowed a better understanding of the role of the two main structures. The Timpa di Santa Tecla is the most seismogenic structure in the area and probably played a role in the magma transfer process for the 1989 eruption. Modifications of the local stress field by actions of this feature may have produced gravitational instability along a second structural system (the Timpa di S. Leonardello) with a time delay of about 100 days. By contrast, magma penetration associated with the larger eruption of 1991–1993 had a deeper rise system and had no effect on local stress conditions, consequently there was no correlation between volcanism and seismicity.