The Energy Emissions as Fracture and Seismic Precursors

The main purpose of this Doctorate Thesis is to set-up a multi-parameter monitoring system that takes into account the observation of several seismic precursors. A seismic precursor is a phenomenon which can take place largely in advance to quake occurrence, and also at large distance from the epicentre. It is well known that the dimension of the earthquake preparation area is a function of the magnitude of the incoming quake and it can consist in a geographical zone up to thousands of kilometres. Furthermore, these precursory phenomena are of various nature but, despite their obvious diversity, many of them reflect a common physical origin. In the last decades a great number of laboratory tests and experimental observations evidenced that mechanical, electromagnetic and neutron emissions, together with radon levels, carbon dioxide emanations and temperature variation, are the most reliable natural phenomena that can be linked to earthquake preparation. In the finalization of this research many experimental tests were conducted both on the laboratory rock samples, and in a suitable monitoring site. First of all, specific tests carried out in the Fracture Mechanics Laboratory of the Politecnico di Torino are presented. Through these tests it was possible to demonstrate that the failure phenomena, in particular when they occur in a brittle way, i.e. with a mechanical energy release, emit additional forms of energy related to the fundamental natural forces. By subjecting brittle or quasi-brittle materials, such as rock specimens, to mechanical stress tests, bursts of neutron emission (NE) during the failure process were produced, necessarily involving nuclear reactions, besides the well-known acoustic emission (AE), and the phenomenon of electromagnetic radiation (EME). The main idea is that, if all these phenomena are simultaneously analysed in suitable monitoring sites, they could provide the basis for prediction of the three main parameters of an earthquake: place and time of occurrence, and magnitude of the seismic event. The place where it occurs is to be understood around the monitoring site, and in an area where its effects are always instrumentally perceptible. Nevertheless, the most important problem with all these precursors is to distinguish signals from noise. A single precursor may not be helpful, the prediction program strategy must involve an integral approach including different precursors. For the in-site monitoring the "San Pietro - Prato Nuovo" gypsum mine located in Murisengo (Alessandria, Italy) was chosen. In this mine, to avoid interference with human activities, the instrumental control units have been located at one hundred meters underground. Finally, the experimental results obtained from July, 1st 2013 to December, 31 2015 (five semesters) are reported. The experimental observations reveal a strong correlation between acoustic, electromagnetic, and neutron emission peaks and the major earthquakes occurred in the closest areas.