Solar-lunar-terrestrial interactions: Bursts of neutron
emission and seismic activity
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
Abstract
In 1990-1991 an increase in the neutron emission
intensity was observed at the new Moon and full Moon in seismically
active regions of the Pamir mountains. In 1997, principally new data
indicating that neutron bursts result from tidal phenomena in the
Earth's crust were obtained. On the other hand, it is known that
tidal forces can act as a triggering mechanism for seismic
activity. Examination of homogeneous global data on earthquakes for
1964-1992 allowed us to reveal a 2-week lunar periodicity of
earthquakes associated with the new Moon and full Moon phases. A
further study of neutron bursts and their correlation with seismic
activity can lead to the formulation of a new type of precursors of
an increase in seismic activity: neutron bursts due to
solar-lunar-terrestrial gravitational interactions.
1. Introduction
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.
2. Observations
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Figure 1
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An important role of tidal forces acting on the Earth's crust
in
the formation of neutron bursts can be demonstrated using
measurements carried out in 1997 in the Pamir mountains in the
region of Jerino at a height of 1100 m above sea level, 30 km to
the north of Dushanbe.
Figure 1 shows daytime measurements of the
counting rates of neutrons
Nn and electrons
Ne with energies
Ee
150 KeV
conducted from 16 to 26 July 1997. From 16 to 24 July
the approximating dashed curve passes approximately
through the maximum neutron counting rates during every day. This
value is the highest on 20 July at 0537 UT (
03 min).
On the same day
the Moon passed through the full Moon phase at 0320 UT.
An increase
in the neutron counting rate at the maxima during the period
16-20 July and a subsequent decrease till 24 July can be due
to
matched tidal effects of the Moon and the Sun. The sum of these
effects reaches its maximum at a full Moon and decreases in
subsequent days, which probably demonstrates the sensitivity of
neutron emission to relatively small variations in tidal forces. At
night (local time) from 21 to 22 July, measurements of neutrons
and electrons were also carried out. The results are shown in
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Figure 2
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Figure 2.
From 1722 UT to 1909 UT on 21 July, approximately 12
hours after the daytime 21 July burst, a multi-impulse burst of
neutron emission exceeding at its maximum the background value by a
factor of 100 was detected. The maximum value of the neutron burst
in the daytime on 22 July was also reached in approximately 12
hours after the nighttime burst. Thus a 12-hour periodicity in the
bursts of 21 and 22 July corresponding to the tidal wave
period was observed.
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.
3. Relation to Seismic Activity
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
25
o N and 5
o 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
40-41
o 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
40
o. At the same time, series appeared
at latitudes
>5
oS. 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 40
o S).
Large differences in the time dependence between the high-latitude
(above 40
o) and low-latitude (below 40
o) 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: 40
o N correspond to 10
o 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.
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Figure 3
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As a result, we have come to a new edition of the hypothesis:
large series of earthquakes with magnitudes
mb 4 and epicenters located
at latitudes of
40
o N or
10
o S begin predominantly
on the days of new and full moon or adjacent days.
To check this hypothesis, the time dependence of
nine earthquake series corresponding to the assumptions
of the hypothesis is been considered
(
Figure 3,
right).
Figure 3
shows that some series have a complicated time profile, but all
of them begin in the days of full or new Moon or within 3 days
(the beginnings of the first and eighth series are 1 and 2 days
from the new Moon, respectively).
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.
4. Summary
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 40
o N and southward of 10
o 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.
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