Editing Earthquake prediction (section)

====== Disturbance of the daily cycle of the ionosphere ======
[[File:LAQUILA 2009 ULF.JPG|thumb|upright=1.5|The ULF* recording of the D layer retention of the ionosphere which absorbs EM radiation during the nights before the [[2009 L'Aquila earthquake|earthquake in L'Aquila, Italy on 6/4/2009]]. The anomaly is indicated in red.]]
The [[ionosphere]] usually develops its lower [[Ionosphere#D layer|D layer]] during the day, while at night this layer disappears as the [[Plasma (physics)|plasma]] there turns to [[gas]]. During the night, the [[Ionosphere#F layer|F layer]] of the ionosphere remains formed, in higher altitude than D layer. A [[Waveguide (radio frequency)|waveguide]] for low [[High frequency|HF]] radio frequencies up to 10&nbsp;MHz is formed during the night ([[skywave]] propagation) as the F layer reflects these waves back to the Earth. The skywave is lost during the day, as the D layer absorbs these waves.

Tectonic stresses in the Earth's crust are claimed to cause waves of electric charges<ref>{{Harvnb|Freund|Takeuchi|Lau|2006}}.</ref><ref>{{Harvnb|Freund|Sornette|2007}}.</ref> that travel to the surface of the Earth and affect the ionosphere.<ref>{{Harvnb|Freund|Kulahci|Cyr|Ling|2009}}.</ref> [[Ultra low frequency|ULF]]* recordings{{efn|1=The literature on geophysical phenomena and ionospheric disturbances uses the term ULF (Ultra Low Frequency) to describe the frequency band below 10 Hz. The band referred to as ULF on the Radio wave page corresponds to a different part of the spectrum frequency formerly referred to as VF (Voice Frequency). In this article the term ULF is listed as ULF*.}} of the daily cycle of the ionosphere indicate that the usual cycle could be disturbed a few days before a shallow strong earthquake. When the disturbance occurs, it is observed that either the D layer is lost during the day resulting to ionosphere elevation and skywave formation or the D layer appears at night resulting to lower of the ionosphere and hence absence of skywave.<ref>{{Harvnb|Eftaxias|Athanasopoulou|Balasis|Kalimeri|2009}}.</ref><ref>{{Harvnb|Eftaxias|Balasis|Contoyiannis|Papadimitriou|2010}}.</ref><ref>{{Harvnb|Tsolis|Xenos|2010}}.</ref>

Science centers have developed a network of VLF transmitters and receivers on a global scale that detect changes in skywave. Each receiver is also daisy transmitter for distances of 1000–10,000 kilometers and is operating at different frequencies within the network. The general area under excitation can be determined depending on the density of the network.<ref>{{Harvnb|Rozhnoi|Solovieva|Molchanov|Schwingenschuh|2009}}.</ref><ref>{{Harvnb|Biagi|Maggipinto|Righetti|Loiacono|2011}}.</ref> It was shown on the other hand that global extreme events like magnetic storms or solar flares and local extreme events in the same VLF path like another earthquake or a volcano eruption that occur in near time with the earthquake under evaluation make it difficult or impossible to relate changes in skywave to the earthquake of interest.<ref>{{Harvnb|Politis|Potirakis|Hayakawa|2020}}</ref>

In 2017, an article in the ''Journal of Geophysical Research'' showed that the relationship between ionospheric anomalies and large seismic events (M≥6.0) occurring globally from 2000 to 2014 was based on the presence of solar weather. When the solar data are removed from the time series, the correlation is no longer statistically significant.<ref>{{cite journal |last1=Thomas |first1=JN |last2=Huard |first2=J |last3=Masci |first3=F |title=Thomas, J. N., Huard, J., & Masci, F. (2017). A statistical study of global ionospheric map total electron content changes prior to occurrences of M≥ 6.0 earthquakes during 2000–2014 |journal=Journal of Geophysical Research: Space Physics |date=2017 |volume=122 |issue=2 |pages=2151–2161 |doi=10.1002/2016JA023652 |s2cid=132455032 |ref=Thomas et al 2017|doi-access=free }}</ref> A subsequent article in ''Physics of the Earth and Planetary Interiors'' in 2020 shows that solar weather and ionospheric disturbances are a potential cause to trigger large earthquakes based on this statistical relationship. The proposed mechanism is electromagnetic induction from the ionosphere to the fault zone. Fault fluids are conductive, and can produce [[telluric current]]s at depth. The resulting change in the local magnetic field in the fault triggers dissolution of minerals and weakens the rock, while also potentially changing the groundwater chemistry and level. After the seismic event, different minerals may be precipitated thus changing groundwater chemistry and level again.<ref name="auto"/> This process of mineral dissolution and precipitation before and after an earthquake has been observed in Iceland.<ref>{{cite journal |last1=Andrén |first1=Margareta |last2=Stockmann |first2=Gabrielle |last3=Skelton |first3=Alasdair |title=Coupling between mineral reactions, chemical changes in groundwater, and earthquakes in Iceland |journal=Journal of Geophysical Research: Solid Earth |date=2016 |volume=121 |issue=4 |pages=2315–2337 |doi=10.1002/2015JB012614 |bibcode=2016JGRB..121.2315A |s2cid=131535687 |ref=Andrén et al 2016|doi-access=free }}</ref> This model makes sense of the ionospheric, seismic and groundwater data.