M. Bottiglieri

Multiple-Time Scaling and Universal Behavior of the Earthquake Interevent Time Distribution

The interevent time distribution characterizes the temporal occurrence in seismic catalogs. Universal scaling properties of this distribution have been evidenced for entire catalogs and seismic sequences. Recently, these universal features have been questioned and some criticisms have been raised. We investigate the existence of universal scaling properties by analyzing a Californian catalog and by means of numerical simulations of an epidemic-type model. We show that the interevent time distribution exhibits a universal behavior over the entire temporal range if four characteristic times are taken into account. The above analysis allows us to identify the scaling form leading to universal behavior and explains the observed deviations. Furthermore, it provides a tool to identify the dependence on the mainshock magnitude of the c parameter that fixes the onset of the power law decay in the Omori law.

Strombolian volcanic activity as an intermittent phenomenon

Considering the characteristics of the Strombolian behaviour and the classical intermittency, we suggest that the well-known superposition of tremor and explosion-quakes of the volcanic activity can be described as an intermittent phenomenon. Indeed, a slightly modified non-linear map of Venkataramani et al. (Phys. Rev. Lett., 77 (1996) 5361), characterized by an intermittent behaviour, reproduces the statistical features of the experimental time series associated with the Strombolian activity, matching the distributions of the amplitude (size) and of the inter-times between two successive explosions.

Comparison of branching models for seismicity and likelihood maximization through simulated annealing

[1] Stochastic branching models provide a good description of some aspects of the temporal organization in seismicity. Generally, they assume that magnitudes are independent of history, as in the widely used Epidemic Type Aftershock Sequence (ETAS) model. Here, we consider a recent epidemic‐like model where time‐magnitude and magnitude‐magnitude correlations are introduced via a dynamical scaling (DS) hypothesis, namely, the magnitude difference between earthquakes fixes the time scale for correlations. We also consider a variation of the ETAS model where the c parameter of the Omori law is not fixed but depends on the parent magnitude. We develop a novel procedure to maximize the log likelihood of the different models. This method is based on a Monte Carlo sampling in the parameter space with a variable step size during the evolution to converge to the given accuracy. The log likelihood indicates that the DS model provides the best fit for the major California sequences and the whole catalog, setting as lower magnitude thresholds Mc ≥ 3.5. For Mc = 3, the best fit is obtained by a model with c depending on both the parent magnitude and goes into Mc as in the generalized Omori law. The better performance of the DS model with respect to the ETAS model is attributed to correlations in magnitudes.

ANALOGICAL MODEL INFERRED FROM TIME DOMAIN ANALYSIS AND GENERATING ORGAN PIPES SELF SUSTAINED-TONE

We have recorded acoustic signals emitted by organ pipes in a variety of experimental framework. We have analyzed the recorded sounds with nonlinear techniques in time domain. Starting from this analysis we have extracted their relevant characteristics. Finally, we have constructed simple and suitable analogical model, able to reproduce the registered waveform and sound in listening.

THE GENERALIZED OMORI LAW: MAGNITUDE INCOMPLETENESS OR MAGNITUDE CLUSTERING

The investigate the aftershock decay soon after the largest ten sequences occurred in Southern California in last 20 years. We show that this decay becomes independent on the mainshock magnitude MM and on the lower magnitude threshold MI if time is rescaled by an appropriate time scale fixed by the difference MM – MI. This result supports the idea that the missing of recorded earthquakes in first part of aftershock sequences is not an artefact due to catalog incompleteness but a real physical effect. We show that a recently proposed dynamical scaling relationship can reproduce the aftershock decay experimentally observed. This approach gives prediction also in agreement with recent results for the organization of aftershocks after small or intermediate magnitude mainshock in Japan.