Infrared Emission from rocks in the Thermal Infrared (TIR) window
European Physical Journal: Special Topics
Satellite data provide ground surface temperatures based on the intensity of the thermal infrared (TIR) emission. TIR anomalies that appear to be related to impending earthquake activity were first reported more than 25 years ago. They can reach 10–15 K. To account for such temperature anomalies, it has been widely assumed that, prior to major earthquakes, warm gases or radon are emanating from the ground around the future epicenter. Here a radically different explanation is presented based on the growing evidence that rocks in the Earth's crust contain peroxy defects in their constituent mineral grains. Peroxy defects consist of pairs of tightly coupled O− such as in O3Si-OO-SiO3. Upon application of stress the electrically inactive peroxy defects can break up, releasing highly mobile electronic charge carriers: defect electrons in the O2-sublattice, called positive holes, symbolized by h•. The h• are the electronic wave function associated with O− in a matrix of O2−. They have the remarkable ability to flow out of the stressed rock volume, spreading fast and far. At the Earth's surface the h• become trapped, preferentially at topographic highs. As they recombine, returning to the peroxy state, IR photons of specific energies are emitted in the Thermal Infrared (TIR) window. In laboratory and field experiments rocks were subjected to stress either by loading one end of a rectangular chunk of a black quartz-bearing diorite via a hydraulic press or by stressing granite boulders from the inside out via expanding BUSTAR cement in boreholes. The TIR emission was recording during the build-up of stress up to failure of the rocks. Principal components analysis and a novel application of fluctuation spectroscopy identified several previously unknown phenomena, in particular a series of TIR emission bands that are consistent with the radiative de-excitation of vibrationally “hot” states of peroxy bonds forming at the rock surface and to pink noise suggestive of electron/hole trapping like in semiconductors.
Physics and Astronomy
John Scoville and Friedemann T. Freund. "Infrared Emission from rocks in the Thermal Infrared (TIR) window" European Physical Journal: Special Topics (2021): 85-109. https://doi.org/10.1140/epjst/e2020-000246-4