Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi

Geological Survey of Finland, Special Paper 46
Vladimir Yevzerov and Svetlana Nikolaeva
in the Holocene. Characteristic features of the morphology,
dimensions and types of the palaeoseismic
deformations allow us to conclude that the intensity
of earthquakes (I) was no less then 7 and possibly 8
or greater according to the MSK-64 scale.
A scheme of ancient earthquake epicenters
(Fig. 2) was made on the basis of geological data
and air photo interpretation. Seismic dislocations
directly indicate residual tectonic deformations in
the epicenter zones of ancient earthquakes, which
are largely concentrated in the west and centre
of the Kola Peninsula. The epicenters of ancient
earthquakes and the epicenters of most historical
and recent earthquakes coincide, which testifi es to
the inherited nature of historical and recent earthquakes.
The epicenters are concentrated in the area
that was occupied by active ice during the Older and
Younger Drays.
The existing knowledge of seismicity of the
region corresponds to a short-term period of instrumental
and macroseismic observations. The
instrumental measurements have been carried since
1956 when the seismic station “Apatity” started to
work. For this period, the region was subjected to
earthquakes with intensities of 3-4 and locally up
to 5. Seismic activity zones are situated in the Kandalaksha
Gulf, on the Murmansk Coast, especially
in the Kola Bay area, and in the Khibiny Mountains.
Information about historical earthquakes is recorded
in archival documents, annals and newspaper publications.
Such events have been known on the Kola
Peninsula since the 17th century. The strongest
The profi le of the Late Weichselian ice sheet had a
low gradient in the Kola region. Therefore, an areal
type of deglaciation dominated for a long time. A
dissecting type of deglaciation took place only in
the Holocene. The epicenters of ancient and modern
earthquakes mainly occupy the territory that was
covered by active ice during the last stages of deglaciation
and was glacioisostatically uplifted with the
greatest speed after deglaciation. Such a distribution
of dislocations is probably explained by the highest
ice surface gradient of the area that was covered
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CONCLUSION
Fig.2. Scheme showing the density of residual deformations,
the epicenters of modern earthquakes and the disposition of
the edge of active ice in the Kola region. Residual deformation
density distribution scale (numerals indicate the number
of residual deformations over an area of 15x15 km): 1 – 1-3,
2 – 3-5, 3 – 5-7, 4 >7; epicenters of 1542-2002 earthquakes,
magnitude M: 5 - ≥5.1; 6 -4.1-5.0; 7 -3.1-4.0; 8 - ≤3. The
disposition of the edge of active ice is shown by a dotted line
(during the Younger Dryas) and continuous line (during the
Older Dryas).
historical earthquake took place in the Kandalaksha
Gulf in 1627 with intensity 8 on the MSK-64 scale.
It is possible to assume that the seismicity of the
study region was, at that time, substantially higher
than today.
by active ice during the Older Dryas and by fast
deglaciation of the territory occupied by active ice
during the Younger Dryas. The general character of
the glacioisostatic uplift has not changed until now
and the elevation continues though its speed was
considerably reduced. Modern and historical earthquakes
are mainly inherited. All these data suggest
that the main reason for the seismicity of the region
is stress resulting from the glacioisostatic uplift of
the Earth’s crust during the deglaciation and postglacial
period.