When the Earth Speaks: Understanding Pre-Earthquake Signals

The “Holy Grail” of all earthquake research is to predict – within limits as narrow as possible – time, place and magnitude of major events. This goal may never be achieved to the satisfaction of some, but we should be able to do better in the future than today. An important step is to get away from the sole reliance on seismology for building probability models. Specifically we need to take into consideration the non-seismic signals, mostly electric or electromagnetic, which the Earth sends out before major quakes – profusely, though not always reliably. Until now, progress has been hindered by a lack of understanding of the physics underlying the generation of these pre-earthquake signals. This is now changing. We discovered that, when rocks are subjected to stress, the stressed rock volumes turn into batteries from where powerful electric currents can flow out. Stress activates dormant electronic charge carriers. These charge carriers are defect electrons in the oxygen anion sublattice, also known as positive holes or p-holes for short. They represent valence fluctuations, O–/O2–. The p-holes travel along the upper edge of the valence band. They can jump grain boundaries. They are persistent and long distance runners. Under the right conditions the p-hole currents can exceed 100,000 A/km3. Understanding the p-hole currents holds the key to deciphering pre-earthquake signals. Deciphering them holds the key to a global earthquake early warning system, provided we invest into more research and are able to pull together resources through a concerted community effort, with strong NASA participation.

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