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So, most of the Earth's crust can become highly conductive if subjected to mechanical stress/shock, for example the type of stress due to the slowing down and opening up of the Earth's lithosphere described above. When high conductivity is reached, electric current can occur between ground regions of different electric potential.1 This current being fed, among other factors, by the change in surface-core E-field mentioned previously.
At this point a second phenomenon called piezo electricity might itervene. Some crystals, in particular quartz which is very frequent in granite rocks,2 will deform if subjected to electric current (that's almost the reverse of the above described phenomenon where mechanical deformation triggers electric current).
One could thus hypothesize that earthquakes are not unlike underground lightning. Earthquakes being to underground electric phenomenon what lightning is to atmospheric electric phenomenon: a simple charge rebalancing process generating some mechanical side effects: air waves (thunder) for lightning and crustal waves (seismic tremors) for earthquakes.
Footnotes:
1 Such effects, combined with emissions of gasses from inside the earth, another consequence of 'opening up', could be another factor in the eruption of anomalous fires and explosions.
2 Interestingly most mountain range are made of granite, concomitantly mountain range are also some of the most quake prone geological formations.
"The new, eastern minimum of the South Atlantic Anomaly has appeared over the last decade and in recent years is developing vigorously. We are very lucky to have the Swarm satellites in orbit to investigate the development of the South Atlantic Anomaly. The challenge now is to understand the processes in Earth's core driving these changes," said Matzka.
Comment: A second sinkhole incident in the same city followed within 2 days, the latter concerning a trapped dog being rescued: