Hazard reduction policies include seismic hazard maps based on probabilistic evaluations and the evaluation of geophysical parameters continuously recorded by instrumental networks. Over the past 25 centuries, a large amount of information about earthquake precursory phenomena has been recorded by scholars, scientific institutions, and civil defense agencies. In particular, hydrogeologic measurements and geochemical analyses have been performed in geofluids in search of possible and reliable earthquake precursors. Controlled experimental areas have been set up to investigate physical and chemical mechanisms originating possible preseismic precursory signals. The main test sites for such research are located in China, Iceland, Japan, the Russian Federation, Taiwan, and the USA. The present state of the art about the most relevant scientific achievements has been described. Future research trends and possible development paths have been identified and allow for possible improvements in policies oriented to seismic hazard reduction by geofluid monitoring.
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