The study of global primary earthquake distribution reveals a normative, primary, tectonic mechanism that is dependant on initial conditions as in all dynamic systems. These trends indicate an underlying system with semi-annual variations and pronounced vernal-autumnal asymmetry. (Fig. 1)
The vernal-autumnal asymmetry exhibits almost twice the number of earthquakes around autumnal equinox as around vernal equinox. However, a number of geomagnetic variation studies have also detected a very clear vernal-autumnal asymmetry (Wilcox and Colburn, 1970; Triskova, 1989). Our study covered 37 years according to the NICE catalog, which we argue is a relatively short period to declare such clear trends. However, the tendency of asymmetry in earthquake numbers has been recorded for more than 22 years of geomagnetic cycles, which might suggest that the number of asymmetric earthquakes occur, on average, over much longer periods.
Our study does indicate, however, how earthquake activity increases during equinoxes and solstices that increase from AE to WS (Figs. 3 and 4). The classic geomagnetic observation shows a maximum at equinoxes when geomagnetic activity occurs slightly after the equinoxes and a minimum at solstices when measured by the intensity of geomagnetic storms. We observed a clear correlation of peaks that occur 4–6 days after equinoxes (Figs. 2 and 3, VE and AE), and solstice peaks 4 days after WS and 4 days before SS, in opposition to the geomagnetic observations. We suggest that opposing solstice trends might relate to the intensity of geomagnetic storms that depend on effective southward components and the polarity of IMF direction to the geomagnetic field. We argue that at a solstice minimum, when poor triggering conditions prevail, there is a low intensity of geomagnetic storms, as described by the RM effect (Russell and McPherron, 1973). We therefore conclude, based on the widely quoted studies on the relationships between the appearances of geomagnetic anomalies and earthquakes, that powerful earthquakes may generate geomagnetic disturbances that develop into geomagnetic storms if the right conditions exist, as in the RM effect, and are probably also affected by the combination of the equinoctial and axial phases (see table).
| VE | SS | AE | WS |
Main shocks (daily peaks) | Mar 24, 25 | Jun 17, 18 | Sep 28, 29 | Dec 25, 26 |
Equinoctial (Dec deg) | Mar 21, 22 Min 0 | Jun 21, 22 Max 23.3 | Sep 22, 23 Min 0 | Dec 21, 22 Max 23.3 |
RM (P angle deg) | Apr 5–8 Max − 26.3 | Jul 7 Min 0 | Oct 8–12 Max 26.3 | Jan 5 Min 0 |
Axial (Bo angle deg) | Feb 25-Mar 15 Max − 7.2 | Jun 6 Min 0 | Sep 7–10 Max 7.3 | Dec 8 Min 0 |
Around the solstices these numbers show an evening off (with 72 shocks around SS and 73 around WS). This symmetrical trend might indicate the insignificance of the tidal effect. However, if the tidal effect does have an influence, we should expect a solstice asymmetry around perihelion on WS when the tidal effect is at a maximum. Although the perihelion (Fig. 4, week 1) does not peak, the daily distribution does indicate peak activity on Jan 1 and 2 (with 10 earthquakes occurring). We are, therefore, unable to rule out completely the gravitational effect that may have only a minor influence on the peaks’ timing.
However, we couldn’t find any explanation for the pronounced peak of earthquake activity that occurs in mid-November (Fig. 3). and we suggest that this phase might indicate the first key to understanding this relationship, Fig. 5 that imply on new cycle that arise from the combination of the three hypotheses.
Finally, because there is no way to distinguish between main shocks and aftershocks our data can only reflect the relative primary mechanism. We suggest that our research is novel and is only at a very early stage. We are open to alternative ways to interpret the data, however, the pronounced correlation above does seem to imply a common magnetic mechanism that probably relates to earth’s core seasonal variation, interaction, and inter-relationship with the magnetosphere and interplanetary magnetic field (IMF).