Displacements Before and After Great Earthquakes: Geodetic and Seismic Viewpoints

In the April issue of Pure and Applied Geophysics, an article on a pilot comparison of pre- and postseismic displacements associated with the most powerful earthquakes based on observations of the global positioning system GPS and networks of seismic stations appeared *.

The data of GPS stations of the Global Navigation Satellite System (GNSS) and the integral characteristics of the local seismic regime, including the accumulated displacements obtained from the catalogs of the earthquake hypocenters’ parameters before and after all mega-earthquakes – 2004 Sumatra-Andaman Mw9.2 in the Indian Ocean, 2011 off the coast of the Tohoku region Mw9.1 in Japan, 2010 on the shelf of the Maule region Mw8.8 in Chile – and the great earthquakes in Chile 2015 west of Illapel Mw8.3, in the Gulf of Alaska 2018 off Kodiak Island Mw7.9, and in New Zealand 2016 nearby the city of Kaikoura Mw7.8.

The authors did not find any noticeable transients in the daily geodetic measurements recorded before the six great earthquakes at the nearest GNSS stations. Nevertheless, (1) in all six cases of the considered strongest earthquakes, a different pattern of the correlation between GPS and seismic displacements before and after the main shocks is observed, (2) the observed high variability of the correlation between geodetic and seismic integrals indicates that earthquakes bring just a partial contribution to the naturally sporadic (Brownian-type) movement of lithospheric blocks of different sizes, and (3) GPS data confirm the existence of intermittent long periods of regionally stable seismicity levels expressed in the values ​​of the control parameter of the Unified Scaling Law for Earthquakes **, the change of which usually occurs as a result of mid- or even short-term bursts of activity associated with catastrophic events.

* Liu T., Kossobokov V.G. Displacements Before and After Great Earthquakes: Geodetic and Seismic Viewpoints // Pure and Applied Geophysics. 2021. DOI:10.1007/s00024-021-02694-2

**  Kossobokov V. Unified Scaling Law for Earthquakes that Generalizes the Fundamental Gutenberg-Richter Relationship // Encyclopedia of Solid Earth Geophysics. Encyclopedia of Earth Sciences Series / Gupta H. (ed). Springer, Cham, 2020. DOI:10.1007/978-3-030-10475-7_257-1