Seismicity of the northern part of Russian plate and its glaciostatic nature

Abstract

The comparison of seismological materials with the front boundary of the latest continental gla� ciation has shown that all revealed really tectonic earthquakes occur exclusively in the occurrence area of a thick cover of this glaciation. The thickness of the glacier at a distance of about 50-100 km from its front could have reached 1 km, and the amplitude of glacioisostatic lowering and subsequent uplifts could have reached 0.3 km. The total amplitude of these movements, which were taking place during 20 thousand years, is comparable with the amplitudes of vertical neotectonic movements, which were taking place during 35- 37 million years and on the average were three orders of magnitude more intense than neotectonic move� ments. With such amplitudes and speeds of vertical glacioisostatic movements, it looks quite plausible that the buried rupture zones could be revived recently (including in Holocene) with block movements of crystalline basement with an amplitude of a few tens of meters. This explains the localization of modern seismicity, which is a hazard to construction, within the occurrence domain of the latest glacial shield. The steady decline in the velocities of glacioisostatic movements after the retreat of the latest glaciation was accompanied by a decrease in the general seismic activity. Against this background, pulsations of seismic activity were recorded in the historical period, the latest phase of its intensification being recorded in the late XX-early XXI century. The general trend toward a decrease in seismotectonic activity in Holocene does not allow the characteristics of early Holocene and more ancient seismodislocations to be used to characterize modern seismicity.