Factors constraining the geographic distribution of earthquake geochemical and fluid-related precursors

Earthquake precursors are elusive, and this elusiveness has hampered earthquake prediction. In this paper, the available catalogues of historical and contemporary geochemical and fluid-related precursors of earthquakes are considered.The locations of recording sites are mapped and compared with data concerning volcanic locations, heat flows, crustal velocities and the depth of seismic events. Possible relations among the considered geophysical parameters and the occurrence of fluid-related earthquake precursors are discussed. Only some geological and geophysical conditions may allow for the occurrence of fluid-related earthquake precursory phenomena. As a consequence, the geophysical models utilized to explain the occurrence of earthquake precursors should be updated. Furthermore, only some areas of the world are deemed suitable for earthquake fluid-related precursor monitoring.