PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
restoration by the day of events. The effect is similar to signal amplitude variations of low-frequency radio
stations.
It allows us to consider such behaviour as typical and try to formulate one of the possible elementary
(primitive) algorithms for the detection of earthquake precursor. A steady increase of atmospherics amplitude
within 4 days was defined as "alert" periods - or, really, the total increase of amplitude for such period must
exceed the mean-square value of amplitude variations for the previous five days multiplied by a correcting factor
(it has been calculated, that it equals 3).
Such an algorithm has been checked up on the Kamchatka peninsula region. Without using of the
earthquakes catalogue at the first stage by data of atmospherics received in Yakutsk for winter periods of 2004-
2006 according to the considered algorithm the possible "alert" days of earthquakes have been defined. The
azimuth 120º (from the northern direction), corresponding to the "center" of Kamchatka has been chosen as the
most probable azimuth on seismic centers (within the limits of fifth Fresnel zone).
The analysis of atmospherics amplitude variations for the specified period has shown 8 "alert" days which
according to the algorithm can be interpreted as a precursor of earthquakes. Then these alert days were compared
with the earthquake catalogue with magnitude more than 4.5, really occurred on the Kamchatka peninsula or in
the nearest region. In Fig. 3 the earthquake epicenters are presented, where "+" represents the earthquakes with
"alert" and "o" - represents the earthquakes with no "alert". One can see, the centers of earthquakes during the
analyzed period were mainly located in two areas, one of which is closer to the chosen direction of atmospherics
arrival. In this area practically all earthquakes have "alert" (5 of 7 days). At the same time, in the other region far
from the selected direction of atmospherics arrival, only two alerts were defined. The recalculation of
atmospherics amplitude in case when the azimuth corresponds to the direction of the second area of earthquakes
gives an increase in probability of correct alerts.
Fig. 3. Location the epicenters of
earthquake with M > 4.3 at Kamchatka
region for winter 2004-2006. The line is
the direction from st. Yakutsk to “center”
of Kamchatka peninsula.
4. Discussion
Thus, a control "blindly" ("in the dark") retrospective analysis using the elementary algorithm of defining
alert days by average atmospherics amplitude has shown that the probability of such short-term forecast of
earthquakes can be up to 60-70 %.
Unfortunately, except the omitted earthquakes during the considered period the algorithm has defined 3
false alerts. To find the possible reasons of such false alerts the Kamchatka volcano activity in these days and
geomagnetic disturbances have been considered. Any specific activity of volcanoes has not been observed. Ар
index is used as the parameter describing geomagnetic disturbances. The behaviour of average values of Ар
index in the previous days by the moment's false alerts, is presented in Fig. 4 where a zero day corresponds to
false alert days. One can see that the false alerts are generated on the 4th day after Ар maximum and they can be
connected with such character of magnetic planetary disturbances. However, if we construct the picture of
behaviour Ар (using the statistical superposed method) for all considered earthquakes (Fig. 5), then it is seen that
against the background of quasi-periodic variations of Ар the event of earthquakes falls on the second day after
the maximum of Ар index.
459