Seismic Events in 2014–2016 around the Karelian Isthmus and Their Nature

Abstract

For the first time in aseismic Leningrad oblast, the local St. Petersburg seismic network recorded 32 compactly localized seismic events with a unique wave pattern and magnitudes МL = –0.6 to +2.1. The nature of the events has been studied, and spectrograms and cluster analysis are used to show the difference between the records of these events and blasts at the Vyborg station. The source parameters and focal mechanism of thrust-strike movement along a possible northwest-trending fault plane were determined, which proves the tectonic origin of the events. Synthetic seismograms of the strongest event on December 18, 2016, at 00:20 have been constructed, the shapes of which correspond to the position of the source at a depth of 2 km. A map of earthquake epicenters has been compiled, and a 4-km-long NS-trending seismogenic zone has been identified as a fault that bounds the Vyborg rapakivi intrusion from the east, and possibly a new rupture that has occurred in near the long- and intensely functioning Erkilja quarry. The regional earthquakes that took place in the historical and instrumental periods of observations have been described. A database of blasts from known quarries has been created. The velocity model has been refined.