![]() The earthquake catalogue currently ( ver. We checked its completeness for M ≥ 5.6 since 1996. In this cases magnitudes are expressed as mb and Ms proxies. It in fact includes all the Global CMT solutions 29, 30 and adds about 10% of events that are missed by the latter. We selected this catalog since it is the only complete one, with homogeneous magnitudes, albeit only from M = 5.6. We choose it since, at the moment, this is the only worldwide data set with homogeneous magnitude estimates that allows for sound statistical analysis. Since our aim was to verify the existence of a link between solar activity and earthquakes, we considered two data sets: worldwide earthquakes, and SOHO satellite proton measurements.Īs far as earthquakes are concerned, we used the ISC-GEM catalogue 28. Statistical assessment of the correlation solar activity–earthquakes Once such a correlation is demonstrated, we propose a tentative, at the moment qualitative, mechanism of possible sun–earthquakes interaction. In this paper, we will definitively establish the existence of a correlation between solar activity and global seismicity, using a long data set and rigorous statistical analysis. However, the large interest nowadays for possible interactions between earthquake occurrence and extra-terrestrial (mainly solar) activity, is testified for instance by the Project CSES-LIMADOU, a Chinese–Italian cooperation aimed to launch a satellite to study from space the possible influence of solar activity and ionospheric modifications on the seismicity 27. On the contrary, 26 argued that there is no convincing argument, statistically grounded, demonstrating solar-terrestrial interaction favoring earthquake occurrence. However, none of these studies allowed achieving a statistically significant conclusion about the likelihood of such mechanisms. Also, some mechanisms have been proposed to justify such correlations: small changes induced by Sun-Earth coupling in the Earth’s rotation speed 23 eddy electric currents induced in faults, heating them and reducing shear strength 24 or piezoelectric increase in fault stress caused by induced currents 25. ![]() Since then, a number of scientists has reported some kind of relationship between solar activity and earthquake occurrence 16, 18, 19 or among global seismicity and geomagnetic variation 15, 20 or magnetic storms 21, 22. The first idea that sunspots could influence the earthquake occurrence dates back 1853, and is due to the great solar astronomer Wolf 17. There is also a smaller number of researchers that studied possible links among solar activity, electro-magnetic storms and earthquakes (e.g. Quite recently, some authors 10 suggested that earthquake occurrence might be linked to earth rotation speed variations. 8, 9) but generalized evidence has never been proven. Many authors have hypothesized that a tidal component may show up in earthquake activity (e.g. Many authors have proposed specific statistical distributions to describe such a non-poissonian behavior 3, 4, 5, 6, 7 but none of these is really satisfactory, probably because the underlying physical process has not been really understood. Worldwide seismicity does not follow a Poisson distribution 1, not even locally 2. This result opens new perspectives in seismological interpretations, as well as in earthquake forecast. A tentative model explaining such a correlation is also proposed, in terms of the reverse piezoelectric effect induced by the applied electric field related to the proton density. The correlation increases with the magnitude threshold of the seismic catalogue. The significance of such correlation is very high, with probability to be wrong lower than 10 –5. We found clear correlation between proton density and the occurrence of large earthquakes ( M > 5.6), with a time shift of one day. In this paper, we analyze 20 years of proton density and velocity data, as recorded by the SOHO satellite, and the worldwide seismicity in the corresponding period, as reported by the ISC-GEM catalogue. Till now, no statistically significant correlation of the global seismicity with one of the possible mechanisms has been demonstrated yet. Large earthquakes occurring worldwide have long been recognized to be non Poisson distributed, so involving some large scale correlation mechanism, which could be internal or external to the Earth.
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