Fifty years of research on earthquakes precursors: lesson learnt and ways forward

The first studies on seismic precursors in Italy date back to seventies. At that time in-situ geotechnical measurements were carried out and the data provided by a tiltmeter located near a large dam in North-eastern Italy revealed the appearance of an anomalous movement in one direction till the occurrence near the dam of the destructive (M=6.5) Friuli earthquake on May 06, 1976. This movement was considered a long-term precursor of the earthquake. From then on, systematic research on the seismic precursors started and one of the first multi parametric network was created gradually in the most seismically active area of Central Italy. The parameters sampled and studied were: 1) micromovements (continuously), 2) Radon content in groundwater (sampled every 10/15 days), 3) flow rate of springs (measured every 19/15 days), 4) deep-resistivity (measured every 10/15 days), 5) electric, magnetic and acoustic emission from ground (continuously), 6) intensity of LF (150-300KHz) radio-signals (continuously). During many years of observations several earthquakes precursors were revealed. In eighties, a cooperation among researchers of Italy, Georgia and Kamchatka started; in this framework the content of ions and gases in the water of deep wells located in those regions, collected for 20 and more years, was analyzed. In 1994 a cooperation between Italian and Japanese researchers started for studying possible disturbances in the propagation of VLF (20-80KHz) radio signals and radio receivers were put into operation in Japan and in Italy. In both the mentioned cases, earthquakes precursors were revealed. In 2009 a European Network (INFREP) for studying the disturbances in VLF-LF radio signals in Mediterranean area was set up. Nine receivers were put into operation in Italy, Greece, Crete, Cyprus, Romania, Turkey, Austria and Serbia and once again several earthquakes precursors were revealed. The Italian multiparametric network was closed at beginning of 2000 leaving to the scientific community the lesson that the way to reveal seismic precursors is the merging of data collected by a multiparametric network. Currently, the INFREP network is still in operation even if faced to maintenance problem due to the aging of receivers. On the basis of the results obtained in Italy and in the word in the last fifty years the forecast of some strong earthquake could be possible if multi parametric networks are deployed and maintained in order to regularly collect and analyze the data. The aim of this presentation is to provide a survey of consolidated results on seismic precursors obtained by different research groups and provide a road map for an operational detection of seismic precursors in the seismic prone areas.