There is one fundamental physical process, overlooked by generations of researchers, that is at the root of most, if not all non-seismic precursory signals: activation of electronic charge carriers deep within the Earth’s crust, when rocks experience ever increasing levels of stress during the lead-up to any major earthquake. Though the pre-earthquake (pre-EQ) stresses occur kilometres, often tens of kilometres below the surface of the Earth, in and around the hypercentre of an oncoming earthquake, the consequences of the stress activation of electronic charge carriers become measurable in multiple ways at the Earth’s surface, in the groundwater, at the ground-to-air interface, in changes in the atmospheric composition, throughout the atmospheric column above the affected area all the way up to the ionosphere. Understanding these pre-EQ signals and recording them allows us to recognize signs of an impending earthquake days to weeks in advance of the potential disaster.
|In this talk, I will discuss the solid-state physics of rocks and earthquake precursors. Earthquake precursor phenomena have been known for some time. They are caused by stresses that build up in crustal rocks. As we have found in the laboratory, these stresses more precisely, differential stresses and strains activate mobile positive charge carriers (defect electrons in the oxygen anion sublattice sublattice: O in a matrix of O2). These positive holes (or pholes for short) flow from the generation region into the surrounding rock. They effectively turn a rock into a giant battery. Under specific conditions, which cause the battery circuit to close, large phole currents can flow. Such currents lead to a variety of phenomena: (i) magnetic field variations and low to ultra-low frequency EM emissions, (ii) ionospheric perturbations over the epicentral region, (iii) air ionization at the ground-air interface and corona discharges with light and radio noise, and (iv) the emission of narrow-band infrared (IR) photons around 10 µm. These excess IR photons are the cause of the so-called thermal IR (TIR) anomaly. Often appearing days before major earth¬quakes, TIR anomalies have been seen from space by NASAs MODIS on TERRA and AQUA, by NOAAs AVHRR and GEOS, by Europes METEOSAT satellites. These various pre-earthquake signals can be used to design an earthquake early warning monitoring system, combining space assets and ground networks.|
All rocks have properties that originate at the atomic level. For example, minerals in most of the rocks in Earth’s crust contain defects known as peroxy defects. In these defects, pairs of oxygen anions have changed their valence from the usual 2– to the unusual 1–. Because peroxy defects are inconspicuous and difficult to detect, they have historically been overlooked by the scientific community. However, when rocks are subjected to stresses that build up prior to earthquakes, these peroxy defects become activated and release electronic charge carriers known as positive holes.
Positive holes are highly mobile electronic charges that turn the rocks into a combination of a battery and a semiconductor. They are electronic charge carriers akin to ‘defect electrons’ in transistors and everyday electronics, but in rocks the positive holes are associated with O– in a matrix of O2–. Once generated in the Earth’s crust due to increasing pre-earthquake stresses, the positive holes have the remarkable ability to rapidly flow through surrounding unstressed rocks. They migrate through the Earth’s crust in a manner analogous to the flow of defect electrons through a semiconductor. They can move at speeds up to 100 meters per second and can travel long distances – tens to possibly hundreds of kilometres. Once the positive holes arrive at the Earth’s surface, they produce multiple physical responses can be detected when they rise above the ever-present background level. These signals are non-seismic, that is, they are not based on acoustic waves due to the rupturing of rocks but on the ability of essentially every rock to let them pass. Though often fleeting and highly variable, these signals are indicators of heightened risk for an earthquake. More than a dozen different kinds of signals have been identified. If we know where to look, how to recognize them, and – most importantly – how to interpret them, these signals can herald the build-up of dangerously high levels of tectonic stress deep below, days and even weeks before major earthquakes.
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