Problems of Engineering Seismology: article

TRIGGERED EARTHQUAKES AT SAMBIA PENINSULA
APTIKAEV FELIX FUADOVICH
ERTELEVA OLGA OLEGOVNA
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Russia, 123242, Moscow, Bolshaya Gruzinskaya st., 10-1
Journal: Problems of Engineering Seismology
Tome: 48
Number: 4
Year: 2021
Pages: 74-88
UDK: 550.34+550.348.436+550.348.098.32
DOI: 10.21455/VIS2021.4-4
Keywords: SAMBIA PENINSULA, KALININGRAD EARTHQUAKES IN 2004, MACROSEISMIC SURVEY, GROUND CONDITIONS, MAGNITUDE, SOURCE, SOURCE DEPTH, ATTENUATION COEFFICIENT, FORESHOCK, MAIN SHOCK, TRIGGER EARTHQUAKE, STRESS STATE
Аnnotation: On September 21, 2004, a series of tangible earthquakes occurred near the city of Kaliningrad. This series of seismic events affected not only the Sambia Peninsula, but also the entire Baltic region up to southern Sweden and eastern Denmark. Instrumentally, only the first 3 events were recorded, a foreshock with a magnitude of 5.0, a main shock with a magnitude of 5.3, and several aftershocks. The above magnitude estimates correspond to the highest values given by various agencies. The magnitude estimates are conservative, but in this case, it is even more difficult to explain the abnormally high intensities in some locations. Abnormally high seismic effects can be given only two explanations: either the influence of the geological structure of the environment, or the appearance of new earthquakes, the trigger for which was the foreshock and the main shock. The first assumption is not supported by the results of seismic microzoning. The maximum amplification of seismic intensity was only 0.6 points at two sites. And the observed amplifications of seismic waves correspond to more significant effects. The authors tried to find factual material confirming the possibility of trigger earthquakes caused by the foreshock and the main shock. The article analyzes the distribution of the seismic effect of the Kaliningrad earthquakes on September 21, 2004 in the Kaliningrad region. The observed intensities are compared with the calculated seismic effects in points of the seismic intensity scale. As a result, it was found that the observed level of seismic effects significantly exceeds the calculated one and cannot be explained as a consequence of the foreshock and the main shock. During the macroseismic survey on the territory of the Kaliningrad region, excessively large cracks in the ground with significant horizontal movements, an anomalous lowering of the water level in the reservoir (a pond near the village of Veselovka) were revealed despite the torrential rains the day before. According to macroseismic data, the average value of the attenuation coefficient for the region under consideration was b » 2.7, which is significantly lower than the world average. A conclusion was made about the stress state of the Sambia Peninsula crust. Therefore, the occurrence of trigger earthquakes is quite possible here.