A METHOD FOR STUDYING SEISMOELECTRIC EFFECTS

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• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80-00809A000600390334-8
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 5
• Document Creation Date: December 22, 2016
• Document Release Date: October 18, 2011
• Sequence Number: 334
• Publication Date: May 16, 1951
• Content Type: REPORT

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CLASSIFICATION CONFIDENTIAL CUNFIUtN I IAL
CENTRAL INTELLIGENCE AGENCY REPORT
INFORMATION FROM
FOREIGN DOCUMENTS OR RADIO BROADCASTS CD NO.
DATE OF
INFORMATION 1950
SUBJECT Scientific - Geophysics, seismoelectric effect
HOW DATE DIST. /6 May 1951
PUBLISHED Bimonthly periodical
WHERE
PUBLISHED Moscow NO. OF PAGES 5
DATE
PUBLISHED Nov 1950
LANGUAGE Russian
THIS DOCUMENT CONTAINS INFORMATION AFFECTING THE NATIONAL DEFENSE
OF THE UNITED STATES WITHIN THE MEANING Of ESPIONAGE ACT SO
U. S. C.. 31 AND SEAS AMENDED. ITS TRANSMISSION ON THE NETELATION
OF ITS CONTENTS IN ANY NANNSN TO AN UNAUTHORIZED PERSON IS PRO-
MINIIED III LAW. 21PR000CTION OF THIS FORM IS PROHINITDD.
SUPPLEMENT TO
REPORT NO.
SOURCE Izvestiya Akademii Nauk SSSR, Seriya Geo ficheskaya 1 Geofizicheskaya,
No ,,1950 pp pp 542-540.
A METHOD FOR STUDYING SEISMOELECTRIC EFFECTS
A. G. Ivanov
Submitted 9 Jun 1950
LF-igures referred to are appended]
Introduction
At present, geophysicists are confronted with the complex problem of develop-
ing methods for forecasting earthquakes. Various methods of geophysical observa-
tions are used for this purpose, e.g., seismic, acoust'..c, gravimetric, magnetic,
electric, etc.
The basic task in studies of geop"l:ysical fields in seismically active regions
is the isolation of the anomalous changes in time which are of a local nature
from factors of a general type which act in equal strength over a large section
of the earth's surface; e.g., in connection with distant effects in the ionosphere,
with general changes of the geomagnetic field, etc. The latter are usua]'.y quite
intense, and it is therefore difficult to study weak changes of a field result-
ing from local causes when these general factors are present.
It is obvious that large changes of geophysical fields in a region where an
n ' earthquake is about to occur will proceed very slowly, since they are caused by
slow changes of local elastic stresses in the earth's crust and the crust's slow
deformation. The rapid perturbations of geophysical field.3 which may accompany
slow changes, especially just before the elastic limit of the given. section of
the earth's crust is reached, are secondary effects of the process under study
and probably have relatively lower intensity.
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CCtlF~ EIJTIAL
The Compensation Method
In the study of the seismoelectric, effect of the second type (A.G. Ivanov,
Izv AN SSSR, Ser Geograf i Geofiz, No 5, 1940; DAN, Vol 7IXIV, No 1, 1939), i.e.,
the emergence of elect^ic potential differences in rocks when elastic waves pass
through them, electrical interference in the earth in the form of rapidly chang-
ing currents is a great hindrance. This interference is so great that up to 10
kg of explosives had to be used at distances from 50-100 m from the observation
point to excite a seismoelectric effect of sufficient intensity.
Careful study of the distribution of electrical interference over a consider-
able surface made Jointly with A. M. Alekseyev (Izv AN SSSR, Seriya Geograf i.
Geofiz, No 5, 1940) showed that for observations in exactly the same azimuth,
the form of interference on the oscillogram was approximately alike for two re-
motely separated regions and that the current changes are basically synchronous
in phase.
These observations indicate first that the cause of the electrical inter-
ference is the same for the entire region studied end second that the reason is
apparently connected with phenomena occurring far from the observation point.
In this article, we will not touch upon the interesting problem of the nature
of the effects causing this interference.
On the basis of the experiments, the author succeeded in using the compensa-
tion method to eliminate the influence of general interference. This method
permitted us to i7-re?:ae greatly the unit's sensitivity to local seismoelectric
~ -
LL1DY... ua bau OIIG CD, ucl:0 tioc of explosions.
In this method, a second supplementary pair of electrodes is installed at
a great distance from the firat main pair of receiving electrodes, but exactly
in the same azimuth. The current oscillations from the second pair are trans-
mitted to the input of the receiving unit in the opposite phase to the oscilla-
tions in the circuit of the main pair of electrodes. In a record case of good
compensation, a clear recording of a seismoelectric effect of the second kind
was obtained in the explosion of only a detonator alone (in water) at a distance
of 100 m from the observation point.
Conditions Governing Use of Compensation Method in Study of Earthquake Predecessors
The use of the compensation method when we change to the study of electrical
effects connected with earthquakes is complicated by the relatively greater dis-
tance from the centrum to the observation point (tens of kilometers and more).
To obtain a complete compensation effect, therefore, the electrodes of the com-
pensating line should be separated by a very great distance to fulfill the con-
ditions required for a change from (a) the model experiments, described above,
with elastic waves caused by near explosions, to (b) observations connected with
earthquakes. The organization of such studies is very difficult. For these pur-
poses, we might attempt to use continuous transmission of current changes from
one point to another, not along conductors, but by radio, with the oscillations
being combined at the receiving points. Such a system has not yet been devised,
however.
Practical considerations force us to separate the pairs of electrodes by
relatively small distances (up to several kilometers).
We assume that the electrical effect of an approaching earthquake can be
represented at the earth's surface roughly by the field of a system of two
charges. We place one charge in the region of the centrum at a depth h beneath
the surface, and the other (of opposite sign), directly beneath it at a distance
..'from the centrum. The charge magnitude is considered equal to one electro`
static unit.
GO~FIBENTIAL
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The values of the first and second derivatives of potential with respect to
distance & (the epicentral distance) on the surface will then be of the form'
c~ 0 --L(42+ h2) Z f Q (L~2+1h E) % `
dd -
af (d2+hz) z +(d2+0ti-,L-0J
f Jdd2(tlz-~-h2)-2 -jd~~d'~l~tif~)~~
The values for the special cases A = 0,.Qk oo.etc., can easily be found from
(1) and (2). It is interesting to note that E--"=O in the region of the
epicenter. This indicates that the ordinary observation of only the potential
gradient of the earth current field at one point may not always be effective in
the detection of the electrical predecessors of earthquakes. Recording of the
second derivative , which can be accomplished by the compensation method
proposed, becomes very important in this case. We expect that such observations,
in certain cases, will produce a better effect than the ordinary measurements.
Figure 1 shows the curves for the first and second potential derivatives, cal-
culated culated from (1) and. (2) for the cases ,Q= h (solid lines), and
Values of the ratio 4/h-R are plotted along the abscissa.
In the "model" observations under field eonditiona. thg Plnatirc. diat?grbanre
caused by the explosion did not reach the position of the compensating pair of
electrodes. In the recording of earthquake predecessors, however, when the
centrum is located at a distance comparable to the spread of the electrode pairs,
the receiving unit will record the difference of the potential gradients in the
two sections where the electrodes are placed, and when the electrode pairs are
brought very close together, its indications will correspond approximately to
the second derivative with respect to.A of the disturbed potential. The receiv-
ing and compensating electrodes can even be moved so close together that the
end electrodes will meet, and thus three electrodes can be used instead of four.
Methods and Equipment Used in Measurements
As was pointed out previously, attention must be given in the study of
earthquake predecessors both to the slow, basic changes of the earth current
field which are due mainly to the process preliminary to the earthquake, and
to the rapier and high-frequency changes which are probably connected with the
critical moment when mechanical stresses in the centrum approach the ground's
elastic limit.
It is obvious that two circuit variations must be used in the electrical
compensation method to solve these two problems. The use of a circuit with a
filter condenser connected in series and a galvanometer of proper period is
recommended for 2I-hr recording on a multiple recording instrument of rapid
oscillations in the band of seismic wave frequencies from about 0.2 to 2 cps.
The author used this circuit in 1940 at the Andizhan seismic station.
The use of a7mirror galvanometer having extra-high sensitivity is recom-
mended for the study of slow changes of earth currents by recording the dif-
ferences of the first potential derivatives or the second potential derivatives.
High sensitivity is required, because the currents which result from combining
(1800 out-of-phase) the end's of the receiving and compensating lines aretweak.
This galvanometer should also have two electrically independent loops firmly
attached to the same mirror galvanometer? then observations could be made by
means of the circuit shown in Figure 2a.
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If the second potential derivative is to be measured, however, we can also
use a highly sen3ltive, single-loop galvanometer if we connect it in a three-
electrode unit, e.g., as shown in Figure 2b.
It is important to keep in mind teat when this method of direct recording
of the second potential derivative or the differences of the potential gradient
is used, electrical interference must be very carefully c:mpensated and the re-
ceiving unit must be adjusted to the highest sensitivity for which the uncom-
pensated interference (background) will cause, on the electrogram, currents in
the form of notable, yet small, changes.
As experience in using the compensation circuit has shown, the most im-
portant coniition for success is that identity in the parameters of the receiv-
ing circuits and symmetry of the circuit be preserved.
It is important to note that, along with the circuit described, the compen-
sation method can be used in a coarser form, e.g-., to eliminate the influence
of changes of only the vertical component of the geomagnetic field on records
of earth currents. This can be doge by using horizontal ungrounded coils of
wire in combination with a receiving pair of electrodes, instead of the compen-
sating pair of electrodes.
In the study of the electrical predecessors of earthquakes by the method
described, we should use two systems of receiving electrodes, recording the
latitudinal and Werldionnl cw p nenta, 1z order to detel4 local electrical
disturbances in any azimuth.
with A. N. Tikhonov'a
? be deoir_able to y^mbine these observations
it - luu u
studies by the profile method in order to obtain more complete information on
the connection of these processes with the deep structure of the earth's crust
and variations of the geomagnetic field. In addition, A. N. Tikhonov, G or-
responding Member of the Academy of Sciences USSR, wrote the author, while re-
viewing the manuscript of this work, that he had derived equations which de-
scribe the electric field in an electrically conducting atmosphere for the case
of arbitrary positioning of electric charges in the earth. We expect that his
calculations will also :lid in quantitative interpretation of earth current ob-
servations which are made by the method cited in this paper.
In conclusion, we wish to thank G. A. Gamburteev, Corresponding Member of
the Academy of Sciences USSR, for his support in making the studies, and also
Professor V. F. Bonchkovskiy, Honored Scientist, for making it possible for
the author to begin work in this field in the Garm expedition of the Geophysical
Institute, Academy of Sciences USSR.
fppended figures follow]
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