Pre-earthquake signals at the ground level

Abstract

Can we really predict earthquakes? Will we be able to do it sometime? The answer to the first question is no, we still cannot predict earthquakes but we seem to be moving in the right direction. At the ground level, several electromagnetic manifestations previous to rupture, are slowly fitting into place. The main theme in this chapter is luminescence and the prevailing hypothesis in the case described here is the electric origin of the phenomenon commonly known as EarthQuake Lights, or EQLs. The difficulty of dealing with luminescence nowadays is separating any EQLs from noise arising from artificial lights, electric short circuits, sparks, even fire from electric power lines, from substations, circuit breakers and the like. The San Lorenzo Island off the coast of Lima, Peru has provided three very outstanding cases of pre-seismic and co-seismic EQLs—with geological consistency—spanning 266 years of observation, including two high magnitude earthquakes. In addition there are three cases linked to low magnitude events with close-by hypocenters, about 2 km, which produces pre-earthquake EQLs on the island. In these cases, the high stress resulting from the build-up of a large magnitude earthquake produced a 21-day anticipation of the EQLs, whereas the low magnitude earthquake gave rise to a short 38 hours lead time. New picture evidence collected at San Lorenzo island show rock formations at an old colonial times prison reported to have been the focus of luminescence evidence before the mega earthquake in 1746. In 2007, a strong M8.0 earthquake 160 km away from the island, produced co-seismic lights, probably via the local activation of positive hole carriers by passing seismic waves, specifically S waves, igneous rocks forming vertical dykes in the bay of Lima. Videos taken by security cameras on the PUCP campus show a very good time correlation with ground acceleration records from a seismometer located on the campus. Videos from an off-campus location show lights that were generated at a hill at the southern end of the city and were confirmed by qualified eyewitnesses. Observations from the San Lorenzo Island point to the possibility that small rocky islets in the Bay could have been the points of origin of columns of light seemingly arising out of the ocean. The deployment of magnetometers, in collaboration with Quakefinder, is currently building up a station network along the seismically very active Southern Peruvian coast. All in all, at least on this side of this subcontinent, luminescence seems to be coupled with the generation and transport of electric charges. The answer to the question whether it will be able to predict earthquakes sometimes in the future is strongly linked to our ability to (i) understand the physics of rocks under stress and (ii) develop a worldwide network of ground stations to collect and process multivariate data that will allow for meaningful deductions of the data leading to predictions. This is the final quest. Wiring different types of sensors to monitor electromagnetic activity prior to earthquakes is the geophysical equivalent to an electrocardiogram except that is aimed at anticipating impending catastrophic seismic activity. Rather than just sensing the passing of mechanical waves, as cardiologists do by "feeling" the cardiac pulse at the wrist, a worldwide web of monitoring stations, combined with the Internet, might bring us early warning signs pointing at future heart attacks of mother Earth.