Geological Hazard Potential at the Baltic Sea and Its Coastal Zone: Examples from the Eastern Gulf of Finland and the Kaliningrad Area - The Baltic Sea Basin - page 338

coasts and marine ecosystems worldwide are caused by natural endogenic and exo-
genic factors or by anthropogenic activities ( www.eurosion.org ; www.encora.org ).
Regarding endogenic processes and connected hazards, the Baltic Sea region is
classified as a low seismicity area, although historical data, covering the period from
1616 to 1911, show the evidence of more than 40 strong (intensity 5-7 MSK-64
scale, 12-point scale of earthquake intensity developed by Medvedev et al. ( 1965 ) )
events in the Baltic region (Nikonov and Sildvee 1991 , Sliaupa et al. 1999 ) . Since
the last seismic activity maximum in 1908-1909, no hazardous seismic events have
been registered here except for the Osmussaare 4.5 magnitude event in Estonia in
1976 (Sliaupa et al. 1999 ) and the Kaliningrad 5.0 magnitude event in September
2004 (Aptikaev et al. 2005 , Assinovskaya and Karpinsky 2005 ) . The seismotec-
tonic activity must have been significantly higher in this region at the time of
deglaciation causing extreme rates of glacial isostatic uplift (Bödvarsson et al.
2006 , Mörner 2004 ) . On the other hand, possible seismic reactivation during the
Holocene has been detected in some old bedrock fracture zones in the Bothnian
Sea, the Archipelago Sea, and the northern Baltic Proper (Hutri 2007 ) . Confirming
evidence comes from high-resolution, low-frequency, echo-sounding observations
of disturbed sediment structures (slide and slumps, faults, debris flow and turbidite-
type structures, and some gas-related structures) and their locations in the vicinity of
bedrock fracture zones (Hutri 2007 ) . In the northern Stockholm archipelago, pock-
marks possibly formed by thermogenic gas seepage were also found over still active
tectonic lineaments in the crystalline basement (Söderberg and Flodén 1991 ) . Some
authors have detected active tectonic faults within the Gulf of Finland (Nikonov and
Sildvee 1991 , Rudnik 1996 , Yaduta 2003 ) .
Marine coastal hazards in the Baltic region have recently become the focus of
attention of many researchers (Valdmann et al. 2008 , Pruszak and Zawadzka 2005 ,
Zilinskas 2005 ) .
The Workshop on Sea-Level Rise and Climate Change organized by TAIEX in
April 2008 demonstrated that the problem of coastal erosion is very urgent for many
Baltic countries (Workshop on Sea-Level Rise 2008 ) , while the coasts of the north-
ern Baltic Sea do not suffer much from coastal erosion due to geological structure,
skerries type of shoreline, and tectonic uplift (Valdmann et al. 2008 ) .
The Estonian coastal zones adjoining the Russian part of the Gulf of Finland have
shown during the last 20-30 years the most marked coastal erosion events resulting
from a combination of heavy storms, high sea level induced by storm surges, ice-free
sea, and thawing sediments (Orviku et al. 2003 ) .
Along the open Latvian Baltic seacoast, the recession has exceeded 50-60 m
(up to 200 m) during the last 50-60 years. Only along the coast of the Gulf of
Riga, coastal erosion is less prominent. In general, coastal erosion has significantly
increased due to severe storms during the last 15 years. The rate of coastal erosion
during any single storm has increased, averaging 3-6 m with the maximum reaching
20 m (Eberhards et al. 2009 ) .
In Lithuania, the total annual sand balance of the coastal zones is negative. The
length of accumulating zones of the Lithuanian coast decreased from 36 to 20 km
between 1993 and 2003, whereas the length of eroded and stable coastal zones