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On recent seismic electrical signal activity in northern Greece
Tectonophysics, 188 (1991) 403-405 Elsevier Science Publishers
ILetter
B.V., Amsterdam
I
Section
On recent seismic electrical signal activity in northern Greece P. Varotsos, K. Alexopoulos and M. Lazaridou Department of Physics, Unioersity of Athens, Solid State Section, Knossou st. 36, Ano Glyfada, Athens I65 61, Greece (Received
January
10,199l;
accepted
January
16,1991)
ABSTRACT Varotsos, P., Alexopoulos, K. and Tectonophysics, 188: 403-405.
Lazaridou,
M., 1991. On recent
seismic
electrical
signal
activity
in northern
Greece.
An extremely important series of SES was recorded on December 31, 1990 at ASS station (close to Thessaloniki). It has the largest amplitude that we have recorded at that station since 1982. This letter includes estimations of the epicenter and magnitude of the impending earthquakes.
In Fig. 1 is shown
a series of Seismic
Electric
have various lengths (i.e. from 70 m to 1 km) and different scales. Dipoles 2 (E-W direction) and 3 (N-S direction) have a length of 70 m and correspond to the scale (in millivolts) shown in the
Signals (SES) that was recorded on December 31, 1990 at the station ASS (lying in the vicinity of Thessaloniki). The six dipoles shown in the figure
Fig. 1. SES activity
0040-1951/91/$03.50
recorded
0 1991 - Elsevier Science
at the station
Publishers
B.V.
ASS on December
31,199O.
404
P.VAROTSOSETAL.
21 I
22 I
23 I
24 I
25 I
26 1 -
Y
E Fig. 2. Areas covered by the selectivity maps of the stations ASS and JOA. The solid dots show the sites The areas a, b and c correspond to the seismic areas from which SES are solely collected at the station (2X-t), Sarnothraki (SAM) and Limnos (Z&f) are also depicted. The large dashed area constitutes selectivity map of the station IOA (for details see Paper 11). The expected epicenter of the SES shown in Fig. 1 should lie either in the area c (with II#%between 5.5 and area a (with M,) larger than 6.0, in accordance to fig. 10 of Paper I).
figure. An inspection of their amplitudes indicates that the ratio of the two components of the variation of the electric field (E) is around unity. We proceed to our estimates concerning the parameters of the impending seismic activity that are based on the aspects developed in our two recent publications, i.e. Varotsos and Lazaridou (1991), hereafter called Paper I, and Varotsos et al. (in press), hereafter called Paper II; these aspects were also presented in a recent International Conference (Varotsos, 1990). We recall that the epicenter determination is based on a number of consecutive steps that combine the following SES-properties: (1) a selectiuity map of the station at which the SES was recorded, (2) polarity and (3) the ratio eEW/eNS of the two SES-components.
of eIectro:elltic stations. ASS; the islands Tbasos the area covered by the 6.0, see the text) or in the
Once the epicenter has been determined, the prediction of the magnitude is made with the help of a log AV/.L. versus the M-plot like that of fig. 10 of Paper 1. During the period in which the SES of Fig. 1 were recorded, only the following four distant stations were in operation: ASS, IOA, PIR and KER. They did not record any simult~eous trace. * Unfortunately the telephone lines connecting the other 14 stations to the central station
* An SES was also recorded at the station IOA but at a di/-ferment time, i.e. at 22 : 22 GMT on Dec. 31, 1990; it should correspond to another seismic activity (M, = 5.0), i.e. in western Greece (around 250 km west of Athens).
ON
RECENT
SES ACTIVITY
of the SES-network
405
IN N GREECE
were interrupted so that their
(and with an factor of 2 smaller amplitude) than
selectivity maps cannot be used in our epicenter
those of Fig. 1. Therefore
determination.
activity
In view of this very serious short-
is not
the impending seismic
an aftershock
and should have
coming the present analysis cannot be considered
epicenters
displaced
by (at least) a few tens of
as equally reliable as that of our earlier predic-
kilometers
far from that of the Dec. 21, 1990
tions reported in Paper I.
earthquake.
Having
also
in
mind
our
earlier
knowledge on the cnw/cNS values of the regions Considerations
for the estimation
of the epicenter
belonging
to the aforementioned
areas a and c,
we could guess the following:
and magnitude
The future The lack of any SES trace at the station IOA precludes the seismic areas depicted in Fig. 2 that correspond to the selectivity map of that station (the procedure according to which a selectivity map is constructed, is described in Paper II). The
epicenters
may lie in the immediate
vicinity of the station ASS
with magnitudes
M of ca.
5.5. Should the epicentral distance r be ca. 50 km from the station ASS (anticlockwise: from east to northwest of Thessaloniki), M could be around 6.0. (Of course, if r is larger, M will be greater in
absence of the current SES activity from PIR and KER also exclude the seismic areas mentioned in
accordance to fig. 10 of Paper I). For the time of the impending seismic activity we refer to fig. 9 of
our earlier papers as being recorded at these two
Paper I according to which the time lag between the initiations of the electrical and the seismic
stations. We have therefore already excluded the following areas: northwestern greece (those regions included in the IOA selectivity map), westem and southwestern greece, the area around Athens, etc. The area around VOL (i.e. the area b of Fig. 2) can also be excluded as its SES are recorded at the station ASS but with a different eEw/eNS ratio (compare with the fig. 4 of Paper I).
activity
is around
may exceed this (e.g. like the case of the KilliniVartholomio destructive earthquakes in 1988 described in fig. 28 of Paper I).
It seems therefore that the following areas should be considered as candidates for the future epicentral
References
zone: the areas a (i.e. between Samothraki, Thasos and Limnos islands in Northern Aegean sea) and
Varotsos,
c (i.e. around Thessaloniki) shown in Fig. 2 of the Paper II. We can further exclude the epicentral zone of a 5.5 earthquake
(EQ;
Dec. 21, 1990),
lying in the vicinity of the Greek Yugoslavian border, i.e. almost 60 km northwest of Thessaloniki, because it emitted SES that were collected at the station ASS but with a different polarity
11 days while the time lag
between the largest SES (i.e. that recorded on December 31, 1990) and the strongest earthquake
quake
P. and Lazaridou, prediction
nals, I. Tectonophysics, Varotsos,
tional
signals,
Conference
els of the Earthquakes,
signals.
Lazaridou,
prediction prediction Paper
Athens,
sig-
M., in prep.
in Greece based on
Electric February
in Greece
presented
on Measurements
Earth’s
on earth-
electric
II.
P., 1990. Earthquake electric
aspects
on seismic
K. and
on earthquake
seismic electric of seismic
based
188 (this vol.): 321-347.
P., Alexopoulos,
Latest aspects Varotsos,
M., 1991. Latest
in Greece
Field
by means
at the Intema-
and Theoretical Variations
6-8,199O.
mod-
Related
to
ILetter
B.V., Amsterdam
I
Section
On recent seismic electrical signal activity in northern Greece P. Varotsos, K. Alexopoulos and M. Lazaridou Department of Physics, Unioersity of Athens, Solid State Section, Knossou st. 36, Ano Glyfada, Athens I65 61, Greece (Received
January
10,199l;
accepted
January
16,1991)
ABSTRACT Varotsos, P., Alexopoulos, K. and Tectonophysics, 188: 403-405.
Lazaridou,
M., 1991. On recent
seismic
electrical
signal
activity
in northern
Greece.
An extremely important series of SES was recorded on December 31, 1990 at ASS station (close to Thessaloniki). It has the largest amplitude that we have recorded at that station since 1982. This letter includes estimations of the epicenter and magnitude of the impending earthquakes.
In Fig. 1 is shown
a series of Seismic
Electric
have various lengths (i.e. from 70 m to 1 km) and different scales. Dipoles 2 (E-W direction) and 3 (N-S direction) have a length of 70 m and correspond to the scale (in millivolts) shown in the
Signals (SES) that was recorded on December 31, 1990 at the station ASS (lying in the vicinity of Thessaloniki). The six dipoles shown in the figure
Fig. 1. SES activity
0040-1951/91/$03.50
recorded
0 1991 - Elsevier Science
at the station
Publishers
B.V.
ASS on December
31,199O.
404
P.VAROTSOSETAL.
21 I
22 I
23 I
24 I
25 I
26 1 -
Y
E Fig. 2. Areas covered by the selectivity maps of the stations ASS and JOA. The solid dots show the sites The areas a, b and c correspond to the seismic areas from which SES are solely collected at the station (2X-t), Sarnothraki (SAM) and Limnos (Z&f) are also depicted. The large dashed area constitutes selectivity map of the station IOA (for details see Paper 11). The expected epicenter of the SES shown in Fig. 1 should lie either in the area c (with II#%between 5.5 and area a (with M,) larger than 6.0, in accordance to fig. 10 of Paper I).
figure. An inspection of their amplitudes indicates that the ratio of the two components of the variation of the electric field (E) is around unity. We proceed to our estimates concerning the parameters of the impending seismic activity that are based on the aspects developed in our two recent publications, i.e. Varotsos and Lazaridou (1991), hereafter called Paper I, and Varotsos et al. (in press), hereafter called Paper II; these aspects were also presented in a recent International Conference (Varotsos, 1990). We recall that the epicenter determination is based on a number of consecutive steps that combine the following SES-properties: (1) a selectiuity map of the station at which the SES was recorded, (2) polarity and (3) the ratio eEW/eNS of the two SES-components.
of eIectro:elltic stations. ASS; the islands Tbasos the area covered by the 6.0, see the text) or in the
Once the epicenter has been determined, the prediction of the magnitude is made with the help of a log AV/.L. versus the M-plot like that of fig. 10 of Paper 1. During the period in which the SES of Fig. 1 were recorded, only the following four distant stations were in operation: ASS, IOA, PIR and KER. They did not record any simult~eous trace. * Unfortunately the telephone lines connecting the other 14 stations to the central station
* An SES was also recorded at the station IOA but at a di/-ferment time, i.e. at 22 : 22 GMT on Dec. 31, 1990; it should correspond to another seismic activity (M, = 5.0), i.e. in western Greece (around 250 km west of Athens).
ON
RECENT
SES ACTIVITY
of the SES-network
405
IN N GREECE
were interrupted so that their
(and with an factor of 2 smaller amplitude) than
selectivity maps cannot be used in our epicenter
those of Fig. 1. Therefore
determination.
activity
In view of this very serious short-
is not
the impending seismic
an aftershock
and should have
coming the present analysis cannot be considered
epicenters
displaced
by (at least) a few tens of
as equally reliable as that of our earlier predic-
kilometers
far from that of the Dec. 21, 1990
tions reported in Paper I.
earthquake.
Having
also
in
mind
our
earlier
knowledge on the cnw/cNS values of the regions Considerations
for the estimation
of the epicenter
belonging
to the aforementioned
areas a and c,
we could guess the following:
and magnitude
The future The lack of any SES trace at the station IOA precludes the seismic areas depicted in Fig. 2 that correspond to the selectivity map of that station (the procedure according to which a selectivity map is constructed, is described in Paper II). The
epicenters
may lie in the immediate
vicinity of the station ASS
with magnitudes
M of ca.
5.5. Should the epicentral distance r be ca. 50 km from the station ASS (anticlockwise: from east to northwest of Thessaloniki), M could be around 6.0. (Of course, if r is larger, M will be greater in
absence of the current SES activity from PIR and KER also exclude the seismic areas mentioned in
accordance to fig. 10 of Paper I). For the time of the impending seismic activity we refer to fig. 9 of
our earlier papers as being recorded at these two
Paper I according to which the time lag between the initiations of the electrical and the seismic
stations. We have therefore already excluded the following areas: northwestern greece (those regions included in the IOA selectivity map), westem and southwestern greece, the area around Athens, etc. The area around VOL (i.e. the area b of Fig. 2) can also be excluded as its SES are recorded at the station ASS but with a different eEw/eNS ratio (compare with the fig. 4 of Paper I).
activity
is around
may exceed this (e.g. like the case of the KilliniVartholomio destructive earthquakes in 1988 described in fig. 28 of Paper I).
It seems therefore that the following areas should be considered as candidates for the future epicentral
References
zone: the areas a (i.e. between Samothraki, Thasos and Limnos islands in Northern Aegean sea) and
Varotsos,
c (i.e. around Thessaloniki) shown in Fig. 2 of the Paper II. We can further exclude the epicentral zone of a 5.5 earthquake
(EQ;
Dec. 21, 1990),
lying in the vicinity of the Greek Yugoslavian border, i.e. almost 60 km northwest of Thessaloniki, because it emitted SES that were collected at the station ASS but with a different polarity
11 days while the time lag
between the largest SES (i.e. that recorded on December 31, 1990) and the strongest earthquake
quake
P. and Lazaridou, prediction
nals, I. Tectonophysics, Varotsos,
tional
signals,
Conference
els of the Earthquakes,
signals.
Lazaridou,
prediction prediction Paper
Athens,
sig-
M., in prep.
in Greece based on
Electric February
in Greece
presented
on Measurements
Earth’s
on earth-
electric
II.
P., 1990. Earthquake electric
aspects
on seismic
K. and
on earthquake
seismic electric of seismic
based
188 (this vol.): 321-347.
P., Alexopoulos,
Latest aspects Varotsos,
M., 1991. Latest
in Greece
Field
by means
at the Intema-
and Theoretical Variations
6-8,199O.
mod-
Related
to