Are There One or More Geophysical Coupling Mechanisms before Earthquakes? The Case Study of Lushan (China) 2013

Abstract

Several possible lithosphere–atmosphere–ionosphere coupling mechanisms before earthquake occurrence are presented in the literature. They are described by several models with different interaction channels (e.g., electromagnetic, mechanics, chemical, thermal), sometimes in conflict with each other. In this paper, we search for anomalies six months before the Lushan (China) 2013 earthquake in the three geo-layers looking for a possible view of the couplings and testing if one or another is more reliable to describe the observations. The Lushan earthquake occurred in China’s Sichuan province on 20 April 2013, with a magnitude of Mw = 6.7. Despite the moderate magnitude of the event, it caused concern because its source was localized on the southwest side of the same fault that produced the catastrophic Wenchuan event in 2008. This paper applies a geophysical multi-layer approach to search for possible pre-earthquake anomalies in the lithosphere, atmosphere, and ionosphere. In detail, six main increases in the accumulated seismic stress were depicted. Anomalous geomagnetic pulsations were recorded in the Chengdu observatory, sometimes following the increased stress. Atmosphere status and composition were found to be anomalous in several periods before the earthquake, and, spatially, the anomalies seem to appear firstly far from the upcoming earthquakes and later approaching the Longmenshan fault where the Lushan earthquakes nucleated. The Formosat-3 data identified interesting anomalies in the altitude or electron content of the ionospheric F2 peak in correspondence with seismic and atmospheric anomalies 130 days before the earthquake. In addition, the total electron content showed high anomalous values from 12 to 6 days before the earthquake. We compared the anomalies and tried to explain their correspondences in different geo-layers by the lithosphere–atmosphere–ionosphere coupling models. In particular, we identified three possible couplings with different mechanisms: a first, about 130 days before the earthquake, with a fast (order of one day) propagation delay; a second, about 40 days before the earthquake occurrence, with a propagation delay of few days and a third from 2.5 weeks until one week before the event. Such evidence suggests that the geo-layers could interact with different channels (pure electromagnetic or a chain of physical-chemical processes) with specific propagation delays. Such results support the understanding of the preparation for medium and large earthquakes globally, which is necessary (although not sufficient) knowledge in order to mitigate their impact on human life.

Atmospheric and Ionospheric Effects of La Palma Volcano 2021 Eruption

“…In particular, in our previous work on activity before the La Palma volcano eruption [5], we proposed that several channels of LAIC can coexist and describe different ways of geophysical interaction. A similar claim has been proposed by Zhang et al [54], investigating in a systematic way the months that preceded the Mw6.7 Lushan (China) 2013 earthquake, identifying a clear chain of anomalies in the lithosphere atmosphere and ionosphere but with different LAIC mechanisms.…”

“…Such an approach was derived from another very similar algorithm, CAPRI [60], with the main difference being the data source: MEANS investigate the climatological archive of MERRA-2 from NASA [61] (the one used in this paper) and CAPRI ERA-Interim and operational archive from ECMWF. Such algorithms have been successfully applied to several earthquakes in the world as well as volcano eruptions [39,54,59,60,62,63].…”

Study on Electron Density Anomalies Possibly Related to Earthquakes Based on CSES Observations

“…By doing so, we can try to explore the universal characteristics of earthquake-ionosphere coupling mechanisms with different seismic source mechanisms and reveal the underlying laws of earthquakes and ionospheric phenomena. Some investigations even suggest that more mechanisms are possible before the same earthquake, as proposed by Zhang et al [34] investigating the Mw6.7 Lushan (China) 2013 earthquake.…”

Observation of the Preparation Phase Associated with Mw = 7.2 Haiti Earthquake on 14 August 2021 from a Geophysical Data Point of View

“…In this paper, we applied several methods to investigate the lithosphere, atmosphere and ionosphere, following the approach we had successfully used before several earthquakes and some volcano eruptions. These cases include among all, the Mw = 6.7 Lushan (China) 2013 [69], Mw = 7.8 Ecuador 2016 [70], Mw = 6.0 and Mw = 6.5 Amatrice-Norcia 2016 [71], Mw = 7.5 Indonesia 2018 [72], Mw = 7.2 Kermadec Islands (New Zealand) 2019 [73] and Mw = 7.8 and Mw 7.5 Turkey 2023 [58] earthquakes. In all of these mentioned cases, a possible lithosphere-atmosphere and ionosphere coupling (LAIC) has been identified in the form of a chain of anomalies and, in some cases (as Lushan 2013), even more possible couplings with different physical mechanisms have been proposed by Zhang et al [69].…”

“…These cases include among all, the Mw = 6.7 Lushan (China) 2013 [69], Mw = 7.8 Ecuador 2016 [70], Mw = 6.0 and Mw = 6.5 Amatrice-Norcia 2016 [71], Mw = 7.5 Indonesia 2018 [72], Mw = 7.2 Kermadec Islands (New Zealand) 2019 [73] and Mw = 7.8 and Mw 7.5 Turkey 2023 [58] earthquakes. In all of these mentioned cases, a possible lithosphere-atmosphere and ionosphere coupling (LAIC) has been identified in the form of a chain of anomalies and, in some cases (as Lushan 2013), even more possible couplings with different physical mechanisms have been proposed by Zhang et al [69]. A sort of confutation analysis showed a lack of lithosphere-atmosphere and ionosphere coupling before a small earthquake, such as the ML = 3.3 Guidonia (Rome, Italy) 2023 event [74].…”