  The starting point of the present review is to acknowledge that there are
innumerable reports of non-seismic types of earthquake precursory phenomena
that are intermittent and seem not to occur systematically, while associated
reports are not widely accepted by the geoscience community at large because no
one could explain their origins. We review a unifying theory for a solid-state
mechanism, based on decades of research bridging semi-conductor physics,
chemistry and rock physics. A synthesis has emerged that all pre-earthquake
phenomena could trace back to one fundamental physical process: the activation
of electronic charges (electrons and positive holes) in rocks subjected to
ever-increasing tectonic stresses prior to any major seismic activity, via the
rupture of peroxy bonds. In the second part of the review, we critically
examine satellite and ground station data, recorded before past large
earthquakes, as they have been claimed to provide evidence that precursory
signals tend to become measurable days, sometimes weeks before the disasters.
We review some of the various phenomena that can be directly predicted by the
peroxy defect theory , namely, radon gas emanations, corona discharges, thermal
infrared emissions, air ionization, ion and electron content in the ionosphere,
and electro-magnetic anomalies. Our analysis demonstrates the need for further
systematic investigations, in particular with strong continuous statistical
testing of the relevance and confidence of the precursors. Only then, the
scientific community will be able to assess and improve the performance of
earthquake forecasts.
