## 1997 |

Hallgass, Riccardo; Loreto, Vittorio; Mazzella, Orfeo; Paladin, Giovanni Earthquakes statistics and fractal faults Journal Article PHYSICAL REVIEW E, 56 , pp. 1346–1356, 1997. Abstract | Links | BibTeX | Tags: earthquakes, hallgass, loreto, mazzella, paladin, self_organization, statistical_physics @article{b, title = {Earthquakes statistics and fractal faults}, author = {Riccardo Hallgass and Vittorio Loreto and Orfeo Mazzella and Giovanni Paladin}, url = {http://pre.aps.org/abstract/PRE/v56/i2/p1346_1, http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=A1997XR16000015&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=0c7ff228ccbaaa74236f48834a34396a}, year = {1997}, date = {1997-01-01}, journal = {PHYSICAL REVIEW E}, volume = {56}, pages = {1346--1356}, publisher = {AMERICAN PHYSICAL SOC}, abstract = {We introduce a Self-affine Asperity Model (SAM) for the seismicity that mimics the fault friction by means of two fractional Brownian profiles (fBm) that slide one over the other. An earthquake occurs when there is an overlap of the two profiles representing the two fault faces and its energy is assumed proportional to the overlap surface. The SAM exhibits the Gutenberg-Richter law with an exponent $beta$ related to the roughness index of the profiles. Apart from being analytically treatable, the model exhibits a non-trivial clustering in the spatio-temporal distribution of epicenters that strongly resembles the experimentally observed one. A generalized and more realistic version of the model exhibits the Omori scaling for the distribution of the aftershocks. The SAM lies in a different perspective with respect to usual models for seismicity. In this case, in fact, the critical behaviour is not Self-Organized but stems from the fractal geometry of the faults, which, on its turn, is supposed to arise as a consequence of geological processes on very long time scales with respect to the seismic dynamics. The explicit introduction of the fault geometry, as an active element of this complex phenomenology, represents the real novelty of our approach.}, keywords = {earthquakes, hallgass, loreto, mazzella, paladin, self_organization, statistical_physics}, pubstate = {published}, tppubtype = {article} } We introduce a Self-affine Asperity Model (SAM) for the seismicity that mimics the fault friction by means of two fractional Brownian profiles (fBm) that slide one over the other. An earthquake occurs when there is an overlap of the two profiles representing the two fault faces and its energy is assumed proportional to the overlap surface. The SAM exhibits the Gutenberg-Richter law with an exponent $beta$ related to the roughness index of the profiles. Apart from being analytically treatable, the model exhibits a non-trivial clustering in the spatio-temporal distribution of epicenters that strongly resembles the experimentally observed one. A generalized and more realistic version of the model exhibits the Omori scaling for the distribution of the aftershocks. The SAM lies in a different perspective with respect to usual models for seismicity. In this case, in fact, the critical behaviour is not Self-Organized but stems from the fractal geometry of the faults, which, on its turn, is supposed to arise as a consequence of geological processes on very long time scales with respect to the seismic dynamics. The explicit introduction of the fault geometry, as an active element of this complex phenomenology, represents the real novelty of our approach. |

## 1996 |

Loreto, Vittorio; Paladin, Giovanni; Pasquini, Michele; Vulpiani, Angelo Characterization of chaos in random maps Journal Article PHYSICA. A, 232 , pp. 189–200, 1996. Abstract | Links | BibTeX | Tags: dynamical_systems, loreto, paladin, pasquini, vulpiani @article{b, title = {Characterization of chaos in random maps}, author = {Vittorio Loreto and Giovanni Paladin and Michele Pasquini and Angelo Vulpiani}, url = {http://www.sciencedirect.com/science/article/pii/0378437196000878 http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=A1996VN65900016&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=0c7ff228ccbaaa74236f48834a34396a}, year = {1996}, date = {1996-01-01}, journal = {PHYSICA. A}, volume = {232}, pages = {189--200}, publisher = {ELSEVIER SCIENCE, AMSTERDAM}, abstract = {We discuss the characterization of chaotic behaviors in random maps both in terms of the Lyapunov exponent and of the spectral properties of the Perron-Frobenius operator. In particular, we study a logistic map where the control parameter is extracted at random at each time step by considering finite-dimensional approximation of the Perron-Frobenius operator.}, keywords = {dynamical_systems, loreto, paladin, pasquini, vulpiani}, pubstate = {published}, tppubtype = {article} } We discuss the characterization of chaotic behaviors in random maps both in terms of the Lyapunov exponent and of the spectral properties of the Perron-Frobenius operator. In particular, we study a logistic map where the control parameter is extracted at random at each time step by considering finite-dimensional approximation of the Perron-Frobenius operator. |

Loreto, Vittorio; Paladin, Giovanni; Vulpiani, Angelo Concept of complexity in random dynamical systems Journal Article PHYSICAL REVIEW E, 53 , pp. 2087–2098, 1996. Abstract | Links | BibTeX | Tags: complexity, dynamical_systems, loreto, paladin, statistical_physics, vulpiani @article{b, title = {Concept of complexity in random dynamical systems}, author = {Vittorio Loreto and Giovanni Paladin and Angelo Vulpiani}, url = {http://pre.aps.org/abstract/PRE/v53/i3/p2087_1 http://samarcanda.phys.uniroma1.it/vittorioloreto/PAPERS/1996/Loreto_PhysRevE_1996.pdf}, year = {1996}, date = {1996-01-01}, journal = {PHYSICAL REVIEW E}, volume = {53}, pages = {2087--2098}, publisher = {AMERICAN PHYSICAL SOC}, abstract = {We introduce a measure of complexity in terms of the average number of bits per time unit necessary to specify the sequence generated by the system. In dynamical systems with small random perturbations, this indicator coincides with the rate K of divergence of nearby trajectories evolving under two different noise realizations. The meaning of K is discussed in the context of the information theory, and it is shown that it can be determined from real experimental data. In the presence of strong dynamical intermittency, the value of K is very different from the standard Lyapunov exponent lambda(sigma) computed considering two nearby trajectories evolving under the same realization of the randomness. However, the former is much more relevant than the latter from a physical point of view, as illustrated by some numerical computations for noisy maps and sandpile models.}, keywords = {complexity, dynamical_systems, loreto, paladin, statistical_physics, vulpiani}, pubstate = {published}, tppubtype = {article} } We introduce a measure of complexity in terms of the average number of bits per time unit necessary to specify the sequence generated by the system. In dynamical systems with small random perturbations, this indicator coincides with the rate K of divergence of nearby trajectories evolving under two different noise realizations. The meaning of K is discussed in the context of the information theory, and it is shown that it can be determined from real experimental data. In the presence of strong dynamical intermittency, the value of K is very different from the standard Lyapunov exponent lambda(sigma) computed considering two nearby trajectories evolving under the same realization of the randomness. However, the former is much more relevant than the latter from a physical point of view, as illustrated by some numerical computations for noisy maps and sandpile models. |

Other subjects