Time and space analysis of two earthquakes in the Appennines (Italy)

Michele Caputo,Giovanni Sebastiani

doi:10.4236/ns.2011.39101

Abstract

In this paper, we study two earthquakes: the April 6th 2009 earthquake of L’Aquila in the region of Abruzzo (Italy) and the 1997 Colfiorito earthquake in the regions of Umbria and Marche (Italy). The data sets of these two earthquakes were analysed in both time and space domains. For time domain we used statistical methods and models both parametric and non-parametric. Concerning the space domain, we used Mathematical Morphology filters. The time domain analysis provides evidence of a possible correlation between seismic activities and the tides of the crust of the Earth. The results obtained show evidence that the daily number of earthquakes of the sequences proceeding and following the April 6th 2009 earthquake of L’Aquila and that of the sequence following the 1997 Colfiorito earthquake have a periodic component of occurrence with period of about 7 days. It seems that the maxima of this component occur at a position of the Moon with respect to the Earth and the Sun corresponding to approximately 3 days before the four main Moon phases. The space domain analysis indicates that the foreshock activity in both earthquakes is clustered and concentrated. Furthermore, in each of the two earthquakes the clusters are located at about 3 kilometers from the epicentre of the main shock.

Highlights

The first concerns the possibility of detecting the effect of the solid Earth tides for the triggering of earthquakes, which we approach with the ansatz that it should be easier to detect the effect of a small perturbation on a system when the system is unstable
The two different sets of aftershocks and a set of foreshocks indicate a possible correlation between the time sequence of events and the stress field generated by the solid Earth tides
The sequences of aftershocks obviously occurred in an unstable stress field due to the previous major shock which destabilized the region, while the sequence of foreshocks occurred in increasing stress field

Summary

Introduction

The first concerns the possibility of detecting the effect of the solid Earth tides for the triggering of earthquakes, which we approach with the ansatz that it should be easier to detect the effect of a small perturbation on a system when the system is unstable. This condition is verified for both foreshock and aftershock sequences. The second issue focuses to contribute to find possible forerunners. To this aim, we analysed the foreshock activity in space domain. From a theoretical point of view the scientists generally considered that the stress generated by the tides in the crust of the Earth could be a direct cause of the triggering, but this is so small that is seemed unlikely that it may help triggering the earthquakes in a perfectly elastic or anelastic Earth crust

Methods

Results

Conclusion