Hydrogeologic and geochemical precursors of earthquakes: an assessment for possible applications

Groundwaters and gaseous emissions have been analyzed in the past with the purpose to contribute to earthquake prediction researches. Main test sites were Japan, U.S.A., former U.S.S.R., China and Turkey. Catalogues of presumed precursory episodes have been compiled over the years and allowed to reach preliminary conclusions about site selection techniques. Controlled experimental sites have recently given the opportunity to better investigate the physical mechanisms originating recorded pre-seismic anomalies. Main characteristics and limitations of hydrogeologic and geochemical parameters are discussed. An in-depth review of results obtained in most relevant test site areas allow to project future instrumental networks oriented to hazard reduction policies.