N. N. Volodichev, B. M. Kuzhevskij, O. Yu. Nechaev, M. I. Panasyuk, A. N. Podorol'sky, and P. I. Shavrin
Nuclear Physics Research Institute, Moscow State University, Moscow, Russia
The correlation between the bursts of low-energy neutron fluxes from the Earth's crust and the periods of passage of the largest tidal waves through the Earth's crust at the new Moon and full Moon discovered in our experiments was explained by Volodichev et al. [1996, 1997]. The essence of the phenomenon is as follows: When the angle between the Earth-Sun and Earth-Moon lines is the smallest, the total gravitational effect exerted by these cosmic bodies on the Earth is the highest and deformations in the Earth's crust are the strongest. This leads to an increase in the neutron concentration in the surface layer of the Earth's crust and atmosphere due to two processes: mechanical emission (that is, a release of various atomic and nuclear particles due to the deformation-induced cracking of the rocks of the Earth's crust) and enhancement of the flow of radioactive gases (isotopes of radon). This leads to a stronger flux of energetic alpha particles that undergo nuclear interactions with the elements of the Earth's crust and atmosphere. As a result, neutrons are ejected.
Earlier we put forward the hypothesis that one of the reasons for formation of neutron bursts at the new Moon and full Moon are increases in the release of radioactive gases. Measurements of fluxes of alpha particles in various regions of the Pamir mountains in July and August 1997 revealed that fluxes of alpha particles were present and that they considerably (by a factor of tens) exceeded the average fluxes in the Earth's crust. The presence of considerable fluxes of alpha particles which are an intermediate product between a radioactive gas and neutrons indicates that an increase in the release of radioactive gases can be a probable reason for neutron bursts.
Since strong neutron bursts were observed at the new Moon and full Moon, that is, when the tidal deformation of the Earth's crust was stronger, it was interesting to obtain the evidence of two-week variations in the seismic activity associated with the Moon's phases. To find a correlation between seismic activity and the new Moon and full Moon phases, the catalog of earthquakes with a magnitude m 4 for 1964-1992 was analyzed. Using the obtained results, we began a systematic search for series of earthquakes. We call a series of earthquakes a set of earthquakes with the epicenters within the area of several square degrees and following each other with a frequency of n, where n is some number of earthquakes per day. At the first stage, when we were looking for a correlation between the Moon phases and seismic activity, we were taking n = 50 per day (or 80 per 2 days). We have found 13 such series during 1964-1992. All the events of the series were located in the Pacific seismic ring: 7 series in its northern part at latitudes 40 o and 6 series between 25o N and 5o S. It was also found that all 6 series at latitudes above 40 o were starting in the days close to the full Moon (the difference was not more than 3 days). The series 7 observed at longitudes of 40-41o began on the fourth day after the full Moon. A hypothesis appeared that large series (with a large number of earthquakes per day) with epicenters at longitudes of 40 o start predominantly on the new or full Moon days or on the days close to them.
To obtain a new earthquake series to check this hypothesis, we began to look for series for which the number of earthquakes were 30 n < 50 per day or 40 n < 80 per 2 days. We have found 24 such series also located in the Pacific belt. However only 4 series were at latitudes 40o. At the same time, series appeared at latitudes >5oS. This fact moved us to widen the hypothesis into the Southern Hemisphere. It would be desirable to find arguments in favor of such uniting of the north and south and also of the asymmetry in the choice of the latitudinal boundaries (since there is no series southward from 40o S). Large differences in the time dependence between the high-latitude (above 40o) and low-latitude (below 40o) regions in 1920-1980 have been reported earlier [see Mogi, 1988, Figure 5.8]. We are able to obtain the latitudinal asymmetry of the seismic activity considering the latitude distribution of the total (for 1964-1992) number of earthquake with mb 4. It was found that the symmetry axis relative the equator is as follows: 40o N correspond to 10o S. Thus the asymmetry in the determination of latitudinal boundaries and the splitting series to high latitude and located at central latitudes all manifest the global distribution of the seismic activity and its time differences between the high-latitude and low-latitude regions. We think that this distribution is due to the geography of the tectonic platforms and the direction of their movement.
The days remote from the days of new or full Moon by 0-3 days are met in a calendar as often as the days remote by 4-7 days. Therefore, if the grouping at the 0-7 interval is homogeneous, the probability of a random grouping of the beginnings of all nine series in one of its half (0-3 days) is equal to 2-9 or 0.002. We believe that this result confirms the hypothesis presented above.
The analysis of the catalogs of earthquakes has shown that the lunar 2-week modulation manifested itself in the large series of earthquakes in the region of the circum-Pacific seismic ring at the latitudes northward of 40o N and southward of 10o S. Our analysis considerably expands the geography of the regions where the 2-week lunar periodicity is observed. It also confirms that the Moon's phase can affect the time of the earthquake onset in the cases when the characteristic time of the energy accumulation before the earthquake is much longer than a month [Allen, 1936]. Deformation of the Earth's crust caused by maximum tidal forces at the new Moon and full Moon can be probably a triggering mechanism for the release of the earthquake energy accumulated during a long period. It is precisely at these days of the synodic months that bursts of neutron emission considerably exceeding (by a factor of tens) the background neutron fluxes are observed in seismically active regions. This suggests that neutron bursts can be regarded as precursors of earthquakes.
Allen, M. W., The lunar triggering effect on earthquakes in southern California, Bull. Seismol. Soc. Am., 26, 147, 1936.
Mogi, K., Earthquake Prediction (in Russian), 382 pp., Mir, Moscow, 1988.
Volodichev, N. N., et al., Scientific discovery: Regularities in variations in the intensity of neutron fluxes from the Earth's crust in seismically active regions at the New Moon and Full Moon, Bull. Supreme Attestation Commission (in Russian), 6, 60, Moscow, 1996.
Volodichev, N. N., et al., Occurrence of neutron intensity bursts at the New Moon and Full Moon, Space Res. (in Russian), 35 (2), 144, 1997.