FLUIDS/TECTONICS RELATIONSHIPS AND THEIR IMPACT ON EARTHQUAKE FORERUNNERS AND FORECASTING

Abstract

The possibility of forecasting seismic events has always attracted people living over earthquake-prone areas, and many empirical methods were proposed in order to predict earthquakes. Even thought some of them successfully predicted an event, none of them never became a reliable forecasting method (Geophys. Jour. Int, 1997). Recent panels and meetings allowed to sum up the situation of the Earthquake prediction and almost all the scientists have agreed that the attempts made all over the world did not provide useful results, thus, statistical approaches to the seismic hazard assessment, continue to offer the most cost-effective means to reduce earthquake-related losses. With the aim to gain a better insight of the processes occurring at various crustal levels during the seismogenesis many research activities based on the information carried by the fluids have been recently developed, although the scientific community have the feeling to be far from any possibility of predicting an earthquake, if “prediction” means the precise indication of time and site hit by the seismic shock. The seismic crisis that recently hit the Central Apennines (Italy, Abruzzo Region) has clearly shown that the role of geochemistry during any seismic emergency is a debated question: the seismological information is provided and used besides potentially useful geochemical information that do not still have a practical role. The long-term geochemical monitoring carried out during the last 15 years over the Italian seismic areas of Northern Italy (Friuli/Slovenia border, Tosco-Emiliano Apennines), Central Italy (Central-Northern Apennines of Umbria-Marche-Abruzzo-Latium Regions), and Southern Apennines (Basilicata-Irpinia area, Calabria Region, Messina strait and Peloritani-Nebrodi Mountains; see references) has allowed to model the origin and circulation of the fluids and to interpret their temporal variations. Fluids, in fact, are natural and fast carriers of information from the deep crustal layers, as such the collected results represent a powerful tool to reveal the presence of hidden structures as well as to evaluate the fault’s activity over seismic-prone areas. In fact, as observed at global scale, any tectonic line under stress deforms before undergoing rupture, and causes modifications to the fluids’ circulation and their geochemical features during the whole seismogenesis. Those modifications may speed up in proximity of rupture events and many geochemical parameters behave as forerunners. The ruptures responsible for the seismic sequences of Umbria-Marche (1997-98) and Abruzzo (2009) taught us how to use the information coming from the fluids. Unfortunately, attempts to move back to old-fashioned earthquake predictions caused alarms due to incorrect use of the scientific information (moreover taking into account only one parameter: radon), and have the consequence of credibility loss of the whole scientific community. With this information in our hands we have to ask to ourselves what the role of geochemistry has to become within the very delicate mainframe of seismic hazard limitation. A long-term monitoring activity aimed to take a census and to define the origin and composition of the circulating fluids for every seismic-prone area, besides the continuous monitoring of selected parameters, makes the necessary geochemical tools to identify the existence of tectonic structures and to evaluate their seismogenic activity