Scientists know much more about what happens after an earthquake (e.g. fault geometry, slip rates, ground deformation) than the various and complex phenomena accompanying the preparatory phases before a seismic event. Pre-Earthquake Processes: A Multi-disciplinary Approach to Earthquake Prediction Studies, a new book just published by the American Geophysical Union, explores different signals that have been recorded prior to some earthquakes and the extent to which they might be used for forecasting or prediction.
The reporting of physical phenomena observed before large earthquakes has a long historyThe reporting of physical phenomena observed before large earthquakes has a long history, with fogs, clouds, and animal behavior recorded since the days of Aristotle in Ancient Greece, Pliny in Ancient Rome, and multiple scholars in ancient China [Martinelli, 2018]. Many more recent case studies have suggested geophysical and geochemical “anomalies” occurring before earthquakes [Tributsch, 1978; Cicerone et al., 2009].
It should not be surprising that a large accumulation of stress in the Earth’s crust would produce precursory signals. Some of these precursors have been correlated with a range of anomalous phenomena recorded both in the ground and in the atmosphere. These have been measured by variations in radon, the electromagnetic field, thermal infrared radiation, outgoing longwave radiation, and the total electron content of the ionosphere.
Earth observations from sensors both in space and on the ground present new possibilitiesEarth observations from sensors both in space and on the ground present new possibilities for investigating the build-up of stress within the Earth’s crust prior to earthquakes and monitoring a broad range of abnormal phenomena that may be connected. This could enable us to improve our understanding of the lead up to earthquakes at global scales by observing possible lithosphere-atmosphere coupling.
For example, the French Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite mission (2004-2010) was the first to systematically study electro-magnetic signals in relation to earthquakes and volcanoes. Earlier in 2018, the China Seismo-Electromagnetic Satellite (CSES-1) was launched, dedicated to monitoring electromagnetic fields and particles. There is also a global initiative to develop and coordinate test sites for observation and validation of pre-earthquake signals located in Japan, Taiwan, Italy, Greece, China, Russia, and the United States of America.
We have carried out statistical checks of historic data to study the correlations between precursor signals and major earthquake events. For example, a decadal study of statistical data for Japan and Taiwan suggested a significant increase in the probability of electromagnetic, thermal infrared, outgoing longwave radiation, and total electron content measurements before large earthquakes [Hattori and Han, 2018; Liu et al., 2018]. A study of satellite data from DEMETER for more than 9000 earthquakes indicated a decrease of the intensity of electromagnetic radiation prior to earthquakes with a magnitude greater than five [Píša et al. 2013, Parrot and Li, 2018]. These results suggest that the earthquake detection based on measurements of these variables is better than a random guess and could potentially be of use in forecasting.
Our book also presents testing of the CN earthquake prediction algorithm for seismicity in Italy [Peresan, 2018], the first attempt of combining probabilistic seismicity models with precursory information [Shebalin, 2018], and the testing of short-term alerts based on a multi-parameter approach for major seismic events in Japan, Chile, Nepal and Iran [Ouzounov et al., 2018]. Further testing is needed to better understand false alarm ratios and the overall physics of earthquake preparation.
Conceptual diagram of an integrated satellite and terrestrial framework for multiparameter observations of pre‐earthquake signals in Japan. The ground component includes seismic, electro-magnetic observations, radon, weather, VLF–VHF radio frequencies, and ocean‐bottom electro-magnetic sensors. Satellite component includes GPS/total electron content, synthetic-aperture radar, Swarm, microwave, and thermal infrared satellites. Credit: Katsumi Hattori, presented in Ouzounov et al, 2018, Chapter 20
Based on our international collaborative work, we found that reliable detection of pre-earthquake signals associated with major seismicity (magnitude greater than 6) could be done only by integration of space- and ground-based observations. However, a major challenge for using precursor signals for earthquake prediction is gathering data from a regional or global network of monitoring stations to a central location and conducting an analysis to determine if, based on previous measurements, they indicate an impending earthquake.
We also found that no single existing method for precursor monitoring can provide reliable short-term forecasting on a regional or global scale, probably because of the diversity of geologic regions where seismic activity takes place and the complexity of earthquake processes.
The pre-earthquake phenomena that we observe are intrinsically dynamic but new Earth observations and analytical information systems could enhance our ability to observe and better understand these phenomena.
Pre-Earthquake Processes: A Multidisciplinary Approach to Earthquake Prediction Studies 2018, 384 pp., ISBN: 978-1-119-15695-6, list price $199.95 (hardcover), $159.99 (e-book)
—Dimitar Ouzounov, Chapman University, USA; email: ouzounov@chapman.edu
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