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The first report of the USA geophysical service on earthquake shocks in the region of the Russian seaside of the Baltic Sea came on September 21, 2004, at 11:05 am (Greenwich). But no one, even the most competent specialists, did expect such strong shocks. And experts at seismological centers of many countries, who registered the earthquake, could not come to a common opinion and localize the epicenters of these geological perturbations. It was only recorded that littoral zones of the East European tectonic platform cushioned the energy released from the seaside. This phenomenon was called the Kaliningrad earthquake. It represented a cascade of tremors of 6 - 7 points. The first two tremors of 4 - 5 and 6 points, respectively, damaged residential houses: their roof tiles, high chimneys and pipes. Eyewitnesses saw triangular waves 0.5 m high (broken water)-a phenomenon arising during water-quakes due to differently directed ground motions in the zone of disturbances.
Such events, as it was mentioned by A. A. Nikonov, Doctor of Geological and Mineralogical Sciences, in the Priroda magazine, were no news to geologists, for it is clearly known that echoes of violent geological activity in the form of low-amplitude waves reach seismically safe regions, the Kaliningrad Region in this case.
It is worth mentioning that stratification and tectonics of the East European tectonic platform were studied and described long ago, in the 1950s - 1980s. Although tectonic fractures of different size and age occur in the basement and all structural levels overlying the cover (in particular, we speak about the Baltic syneclise underlying the given region), this territory is classified as non-seismic (1 - 5 points).
Not so long ago it became necessary to look into the geology and seismism of the affected region. So far it is difficult to make definite conclusions. In its works a research team of the RAS Joint Institute of Physics of the Earth named after O. Yu. Schmidt in Moscow (head of the team Dr. A. A. Nikonov) showed that, as mentioned by the author in Priroda magazine, "activity of rupture zones of the ancient deep deposit near the coastal line of the peninsula, i.e. in its northern latitudinal and western meridional sections of 15 - 25 km, is quite probable.
Intersection of these zones (northwest of the Taran Cape) can be considered to be a tectonic joint of orthogonal fractures with deep roots". And work to detect other foci of geological activity is still underway.
Unfortunately, the geological situation in the region is not yet clear. Scientists have divided its territory into two parts: one, northwest of the Kaliningrad Peninsula, and the other, over to the south, around the Kaliningrad latitude. What we have discovered is that both parts were active during the first and the second, or most intensive, shocks. Further work is in progress.
"In the Wake of the Kaliningrad Earthquake", Priroda, No. 3, 2005
Prepared by O. NESTEROVA
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