European Geosciences Union Seismicity, heat flow and...
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Fig.2. The distribution of the heat flow density, seismicity and the main neotectonic structures in the Barents Region (Grantz, 2011; Alekseev et al, 2004) 18 - Sture Graben; 19- Hippopen-Olga Graben; 20 - Orle Ramp; 21- Franz Victoria Graben; 22 - St.Anna Graben; 23- Voronin Graben; 24 - Kharitont Laptev Basin; 25- Sedov Basin; 26 - Samoilov Basin; 27- Bjornoya Basin; 28 - Nordkapp Basin; 29- West-Barents Basin; 30 - Belomorsky Graben; 31- South-Barents Basin; 32 - North-Barents Basin; 33- Albanov Basin; 34 - Pukhuanskya Depression; 12 - Demidov Bank; 13- Gusinskaya Bank; 14 - Albanov High; 15- Gusinskaya Bank; 16 - Ushakov High; 17- Central-Kara High; Circum offshore faults: 1 - Active spreading centre; 2 - Normal fault offshore; 3 - Extinct spreading centre; 4 - flexure bend-breaking area of the continental shelf and the main tectonic faults; 5 - faults; 6 - boundaries of neotectonic structures; 7 - Svalbard High; 8- Bely and Victoria High; 9 - Persey High; 10- Bjornoya High; 11 - Central Bareats High; A swarm of earthquakes with magnitudes 2.8-3.6 has been observed surrounding the small island White, located between the Spitsbergen and Frantz Josef Land islands. Some events are confined to the boundary of the raising Franz-Victoria and in the area of allocation of neotectonic faults. The implementation of the energy accumulated in the process of deformation of the earth's crust, particularly in subduction zones is related to the slow movements along the faults from a sliding creep before the earthquake (Lay, 2009; Peng and Gomberg, 2010). Presumably, the increased number of earthquakes observed in the mouth of the Graben at the boundary of the continental shelf is a consequence of the discharge. There are several neotectonic faults on the Franz Josef Land islands. Epicenters of seismic events correspond to faults close to the islands. A small part of the earthquake is recorded in the area of the St. Anne Graben. The epicenters are confined to the sides of the graben and the central area of its mouth part. The highest seismic activity of the Arctic Basin is concentrated in the rift zones of Gakkel and Knipovich Ridges (Fig. 2). The special tectonic regime of Knipovich Ridge is characterized by a predominant shear component of the spreading, the volcanic processes are reduced or almost absent (Avetisov, 1996; Dubinin et al., 2013). Fig. 1.Map seismicity, neotectonic Structures and active Faults in the Western Arctic Region Conclusions Thus, the information about the latest seismicity shows the manifestation process activation of the tectonic activity of the Arctic Basin caused by rifting, active stretching lithospheres blocks and volcanic activity. Areas of the Mid-Arctic Ridge, transition zone continent-ocean and sides of the grabens are the most seismic active regions. The weak seismic activities of the Barents-Kara shelf can be explained by ultra-slow speeds of the processes occurring in the lithosphere. Higher values of heat flow in the North- and South-Barents Basins and in the South-Kara Basin, in which the hydrocarbon deposits were allocated, are consistent with the decrease of the lithosphere in this area. The cross-sections C-D. Increased seismic activity is observed in the dislocations collision zone in 2 the Svalbard area, the maximum of heat flow values (484 mW/m ) is due to magmatic intrusions, a thickness of the lithosphere decreases. The heat flow values are above average for Barents High, 2 about 80 mW/m . A mantle boundary goes down to 36 km under the North Barents Basin. North 2 Barents Basin has been formed as a result of local rifting, heat flow values are about 70 mW/m for 2 the continental crust, maximum - 97 mW/m . Seismic activity appears only in the North of the North Barents Basin in the Franz Josef Land archipelago area. In the North-Kara Basin the heat flow 2 values are reduced to 50 mW/m . Seismicity have not been recorded in this area. The aim of this work consist to establish the relationship between a model of the offshore basin structure, the latest earthquakes for 2011- 2014, and available data of the heat flow density of the European Arctic region. Breach of the continental segment integrity of the European Arctic basin by regmatic system breaks have occurred repeatedly and have set up a complex pattern of tectonic blocks with a hierarchical structure. These features was reflected on the map of main neotectonic structures and faults of the European Arctic basin (Fig. 1) (Alekseev et al, 2004; Grantz et al, 2011). The data shows the difference of tectonic structures and a wide scatter of geothermal data getting in this sector of the Arctic Basin and its surroundings. From different sources (Khytorskoy et al, 2013; Davies, 2010; Sundvor, 2000; Okay,1993; The Global Heat Flow Database of the International Heat Flow Commission).) we have created a generalized database of the heat flow values at the Western Arctic basin. We have made an interpolation of values and linked isolines to neotectonic structures (Fig. 2). The analysis of available data obtained by measurements in wells and thermal sounding revealed a tendency for an increase in heat flow in the northeastern and northwestern directions. For example, in the zone of conjugation of the Kola 2 2 micro plate and the Baltic Shield, the heat flow averages 54 mW/m and amounts to 70 mW/m in the region of the North Barents Basin and Central Barents rise. To a first approximation, such a trend in heat-flow variations can be explained by approaching the North Atlantic spreading center, where the thermal activity of the asthenosphere increases. At the same time, our data indicate that the crust of the Barents Plate is subjected to secondary processes, which become younger in the northern direction. For the trough Franz Victoria it was obtained highly contrasting heat flow values, such as anomalously low values (30 and 2 2 34 mW/m ) and abnormally high ones (88 and 97 mW/m ). Such contrasting values measured at very close distances (at the range of 1 ° x 3 °) are typical for areas of evaporates in the sedimentary cover in the destruction of the continental crust. The highest values of the heat flow with the substantial dispersion are characteristic for the ridges Gakkel and Knipovich of the Arctic Basin. It indicates the presence of areas of hydrothermal activity (Zayonchek et al. 2010). At 2 the Orly trough and its continuation within the continental slope the heat flow is 300 to 520 mW/m , which is almost 10 times higher than background levels of heat flow in the Barents Sea (Fig. 2) The morphology and obtained geothermal data for the Orle Trough show that the trough has a tectonic nature. It is likely a rift that penetrates the earth's crust throughout its thickness and is in an active phase of development. A relatively high level of heat flow is observed on the west coast of the Yamal Peninsula and in the South 2 Kara Basin (above 70 mW/m ). These points are associated with gas and condensate fields (Fig. 2). The connection between the localization of hydrocarbons and high heat flow is obvious. Geological-geophysical cross-sections A-B, C-D The geological and geophysical cross-sections of the lithosphere (c ) for some profiles with correlations of heat flow data (a) and recent seismicity (b) have been made for clarify the complex spatial structure and geodynamics of the European Arctic Basin (Fig. 4). The cross-sections A-B was made in meridian direction 40 ° E from the Gakkel Ridge through the Barents Sea shelf and continental part of Northern Europe (Schwartzman, 2008). The cross-sections C-D was made for Svalbard-Franz Josef Land-Tajmyr direction information for most part of which was taken from the deep seismic cross-section 4AR (Sakylina, 2007). The cross-sections A-B. The Gakkel Ridge lithosphere is decreasing to 30 km or less, the crustal 2 thickness is about 10 km, the heat flow values increases from 100 to 500 mW/m . All of these observations confirms the idea that the Gakkel Ridge belongs to oceanic spreading zones with modern volcanism and seismic activity. At the boundary of the shelf the thickness of the lithosphere 2 increases of up to 60 km, heat flow values are reduced to 70 mW/m and the seismic activity is decreased. At the edge of the shelf from Franz Josef Land to the South Barents Sea basin the thickness of the lithosphere increases to 80 km, the Moho from 15 to 25 km and the sedimentary layer - up to 10 km. The Moho is dipped up to 35 km. The values of the heat flow are in the range of 2 60-70 mW/m . In the South Barents Sea basin a background of heat flow is 58-66 mW/m2. Some anomalous 2 values are 114 and 196 mW/m (see. Fig. 1) and can be attributed to the influence of exogenous factors, such as bottom currents. In this area, the lithosphere is reduced to 65 km and in some places - up to 35 km. According to (Artyushkov et al. 2014) there were extension blocks of the lithosphere. The result of the thinning of the lithosphere was the emergence of rifts and grabens. Tectonic processes are accompanied by anomalous heat flow of the upper mantle or mantle diapirs. Also magmatism was developed actively at the origin stage of the rift depressions. The continental part of the cross-sections A-B is characterized by cold lithosphere with thickness more than 200 km, by the continental crust about 40 kilometers and by a relatively thin or missing 2 sedimentary layer. The value of the heat flow is reduced to 30-35 mW/m . Weak seismic activities is observed at the boundaries of major tectonic structures. 30 30 54 114 155 98 198 A В 0 400 800 1200 1600 2000 2400km M 90 >150 Q, mW/m 2 A 80 H, km 20 40 60 0 В 0 400 800 1200 1600 2000 2400km A В 0 400 800 1200 1600 2000 2400km R, град. 10 o -10 o 10 o -10 o Central Bareats High Gakkel Ridge Brusilov Fault Belomorsky Graben Belomorsky Graben Kola Horst Northern European Plain South-Barents Basin basit a) b) c) Fig.4. Geological-geophysical cross-sections A-B and C-D 0 20 40 60 H, km Svalbard Bely and Victoria High Orle Ramp Central Kara High North-Barents Basin D C м a) b) c) 30 90 >150 Q, мВт/м 2 1.2 o -0.7 o -1.2 o 0.7 o 0.4 o 0.75 o 1.5 o 1.86 o R, град. 97 53 80 104 484 0 400 800 1200 1600 km C C D D 0 400 800 1200 1600km 0 400 800 1200 1600km eclogites eclogites ACKNOWLEDGMENTS This work was supported in part by the Ministry of Education and Science of the Russian Federation (project no. RFMEFI61014X0006) - sedimentary rocks - basement rocks - upper mantle 2 - a plot of heat flow, mW / m - fluid-saturated zone of the unconsolidated sedimentary cover - arrays of basites - arrays of eclogites - the epicenters of seismic events, M – magnitude M 54 - Moho boundary - the boundary of lithosphere and asthenosphere by geothermal data - asthenolith, direction of flow 6.0 < < 2.0 2.0-4.0 4.0-6.0 M - North-Barents Basin - South-Barents Basin - South-Kara Basin NB SB SK Legend: Introduction Fig. 3. Map seismicity and active Faults in the Region Nordaustlandet-Bely A rupture of the Earth's crust can be complete within the rift, which is characteristic for ocean rifts and for transition zones from continent to ocean (basites, eclogites) (Kaschybin et al, 2013). Not all of the Earth's crust dives are characterized by a significant stretch (Artyushkov et al. 2015). The distribution of the heat flow in the Western Arctic basin correlates with the capacity of sedimentary cover. The figure 4 represented contour depth to basement in the north-western part of the Eurasian continental margin, where there are (10-20 km) depressions in the Barents-Kara region: SB- South - Barents Sea, NB - North Barents Sea, SK - South Kara (Kaschybin et al, 2011). This data confirms the connection of high heat flow with a maximum dipping of the foundation (see Figure 4). Seismicity, heat flow and tectonics of the West Arctic Basin Irina Basakina (1), Galina Antonovskaya (1), Elena Kremenetskaya (2), Michail Khutorskoy(3). European Geosciences Union General Assembly 2016 Vienna Austria 17-22 April 2016 EGU.eu The Federal Research Center for Integrated Studies of the Arctic Russian academy of sciences Heat flow of the Arctic Basin Seismicity of Arctic region (1) Institute of Environmental Problems of the North, Ural Branch of RAS, Arkhangelsk, Russian Federation (2) Kola Branch of Geophysical Service, Russian Academy of Sciences, Russian Federation (3) Geological Institute, Russian Academy of Sciences, Moscow, Russian Federation A significant contribution to the study of seismicity of the Arctic was made possible by the installation of new stations, located directly in the Arctic zone - "Amderma" (AMD), 2010 and the "Franz Josef Land" (ZFI), 2011. A summary map of seismicity based on the data of the Arctic seismic networks for the years 2011-2014 is presented in Fig. 2. The continental part of the Eurasian plate is characterized by low seismicity. Significant seismic activity occurs in the north of the Barents Sea shelf (Fig. 4), which is characterized by low thickness of lithosphere (35 km) and considerable fragmentation of the continental slope. There is clear evidence that epicenters of earthquakes are confined to the rift valleys. Note that anomalously high heat flow values also are confined to rift structures on North of the Barents Sea. However, spatial coincidence of the anomalies of heat flow and epicenters is unlikely because of high temperature of the lithosphere and its lower viscosity. This, in particular, can explain an absence of seismicity in Orly trough within the Svalbard plate and some seismic activity on the continental slope. An interesting area for the investigation of intraplate seismicity is the Svalbard archipelago. The tectonic setting of this area is unique in that an active spreading ridge (the Knipovich Ridge) lies very near the passive continental margin, and also because the archipelago, as well as the surrounding oceanic areas have a very complex tectonic history. To the west of Svalbard we have the Mid-Atlantic spreading ridge with constant high earthquake activity. To the South-East, is the Storfjorden area which has recently experienced a significant increase in seismic activity. Thus an earthquake of magnitude 6 which occurred on 22 February 2008 was the largest earthquake in the North Atlantic for last 100 years, and was followed by thousands of aftershocks, which continued for more than five years (Pirli et al., 2010). In general, we observe ongoing earthquake activity in most regions of the Svalbard archipelago.
Transcript of European Geosciences Union Seismicity, heat flow and...
Fig.2. The distribution of the heat flow density, seismicity and the main neotectonic structures in the Barents Region
(Grantz, 2011; Alekseev et al, 2004)
18 - Sture Graben; 19- Hippopen-Olga Graben; 20 - Orle Ramp; 21- Franz Victoria Graben; 22 - St.Anna Graben; 23- Voronin Graben; 24 - Kharitont Laptev Basin; 25- Sedov Basin; 26 - Samoilov Basin; 27- Bjornoya Basin; 28 - Nordkapp Basin; 29- West-Barents Basin; 30 - Belomorsky Graben; 31- South-Barents Basin; 32 - North-Barents Basin; 33- Albanov Basin; 34 - Pukhuanskya Depression;
12 - Demidov Bank; 13- Gusinskaya Bank; 14 - Albanov High; 15- Gusinskaya Bank; 16 - Ushakov High; 17- Central-Kara High;
Circum offshore faults: 1 - Active spreading centre; 2 - Normal fault offshore; 3 - Extinct spreading centre; 4 - flexure bend-breaking area of the continental shelf and the main tectonic faults; 5 - faults; 6 - boundaries of neotectonic structures; 7 - Svalbard High; 8- Bely and Victoria High; 9 - Persey High; 10- Bjornoya High; 11 - Central Bareats High;
A swarm of earthquakes with magnitudes 2.8-3.6 has been observed surrounding the small island White, located between the Spitsbergen and Frantz Josef Land islands. Some events are confined to the boundary of the raising Franz-Victoria and in the area of allocation of neotectonic faults. The implementation of the energy accumulated in the process of deformation of the earth's crust, particularly in subduction zones is related to the slow movements along the faults from a sliding creep before the earthquake (Lay, 2009; Peng and Gomberg, 2010). Presumably, the increased number of earthquakes observed in the mouth of the Graben at the boundary of the continental shelf is a consequence of the discharge.
There are several neotectonic faults on the Franz Josef Land islands. Epicenters of seismic events correspond to faults close to the islands. A small part of the earthquake is recorded in the area of the St. Anne Graben. The epicenters are confined to the sides of the graben and the central area of its mouth part. The highest seismic activity of the Arctic Basin is concentrated in the rift zones of Gakkel and Knipovich Ridges (Fig. 2). The special tectonic regime of Knipovich Ridge is characterized by a predominant shear component of the spreading, the volcanic processes are reduced or almost absent (Avetisov, 1996; Dubinin et al., 2013).
Fig. 1.Map seismicity, neotectonic Structures and active Faults in the Western Arctic Region
ConclusionsThus, the information about the latest seismicity shows the manifestation process activation of the tectonic
activity of the Arctic Basin caused by rifting, active stretching lithospheres blocks and volcanic activity. Areas of the Mid-Arctic Ridge, transition zone continent-ocean and sides of the grabens are the most seismic active regions. The weak seismic activities of the Barents-Kara shelf can be explained by ultra-slow speeds of the processes occurring in the lithosphere. Higher values of heat flow in the North- and South-Barents Basins and in the South-Kara Basin, in which the hydrocarbon deposits were allocated, are consistent with the decrease of the lithosphere in this area.
The cross-sections C-D. Increased seismic activity is observed in the dislocations collision zone in 2the Svalbard area, the maximum of heat flow values (484 mW/m ) is due to magmatic intrusions, a
thickness of the lithosphere decreases. The heat flow values are above average for Barents High, 2about 80 mW/m . A mantle boundary goes down to 36 km under the North Barents Basin. North
2Barents Basin has been formed as a result of local rifting, heat flow values are about 70 mW/m for
2the continental crust, maximum - 97 mW/m . Seismic activity appears only in the North of the North Barents Basin in the Franz Josef Land archipelago area. In the North-Kara Basin the heat flow
2values are reduced to 50 mW/m . Seismicity have not been recorded in this area.
The aim of this work consist to establish the relationship between a model of the offshore basin structure, the latest earthquakes for 2011-2014, and available data of the heat flow density of the European Arctic region. Breach of the continental segment integrity of the European Arctic basin by regmatic system breaks have occurred repeatedly and have set up a complex pattern of tectonic blocks with a hierarchical structure. These features was reflected on the map of main neotectonic structures and faults of the European Arctic basin (Fig. 1) (Alekseev et al, 2004; Grantz et al, 2011).
The data shows the difference of tectonic structures and a wide scatter of geothermal data getting in this sector of the Arctic Basin and its surroundings. From different sources (Khytorskoy et al, 2013; Davies, 2010; Sundvor, 2000; Okay,1993; The Global Heat Flow Database of the International Heat Flow Commission).) we have created a generalized database of the heat flow values at the Western Arctic basin. We have made an interpolation of values and linked isolines to neotectonic structures (Fig. 2).
The analysis of available data obtained by measurements in wells and thermal sounding revealed a tendency for an increase in heat flow in the northeastern and northwestern directions. For example, in the zone of conjugation of the Kola
2 2micro plate and the Baltic Shield, the heat flow averages 54 mW/m and amounts to 70 mW/m in the region of the North Barents Basin and Central Barents rise. To a first approximation, such a trend in heat-flow variations can be explained by approaching the North Atlantic spreading center, where the thermal activity of the asthenosphere increases. At the same time, our data indicate that the crust of the Barents Plate is subjected to secondary processes, which become younger in the northern direction.
For the trough Franz Victoria it was obtained highly contrasting heat flow values, such as anomalously low values (30 and 2 234 mW/m ) and abnormally high ones (88 and 97 mW/m ). Such contrasting values measured at very close distances (at the
range of 1 ° x 3 °) are typical for areas of evaporates in the sedimentary cover in the destruction of the continental crust.
The highest values of the heat flow with the substantial dispersion are characteristic for the ridges Gakkel and Knipovich of the Arctic Basin. It indicates the presence of areas of hydrothermal activity (Zayonchek et al. 2010). At
2the Orly trough and its continuation within the continental slope the heat flow is 300 to 520 mW/m , which is almost 10 times higher than background levels of heat flow in the Barents Sea (Fig. 2) The morphology and obtained geothermal data for the Orle Trough show that the trough has a tectonic nature. It is likely a rift that penetrates the earth's crust throughout its thickness and is in an active phase of development.
A relatively high level of heat flow is observed on the west coast of the Yamal Peninsula and in the South 2
Kara Basin (above 70 mW/m ). These points are associated with gas and condensate fields (Fig. 2). The connection between the localization of hydrocarbons and high heat flow is obvious.
Geological-geophysical cross-sections A-B, C-DThe geological and geophysical cross-sections of the lithosphere (c ) for some profiles with correlations
of heat flow data (a) and recent seismicity (b) have been made for clarify the complex spatial structure and geodynamics of the European Arctic Basin (Fig. 4). The cross-sections A-B was made in meridian direction 40 ° E from the Gakkel Ridge through the Barents Sea shelf and continental part of Northern Europe (Schwartzman, 2008). The cross-sections C-D was made for Svalbard-Franz Josef Land-Tajmyr direction information for most part of which was taken from the deep seismic cross-section 4AR (Sakylina, 2007).
The cross-sections A-B. The Gakkel Ridge lithosphere is decreasing to 30 km or less, the crustal 2
thickness is about 10 km, the heat flow values increases from 100 to 500 mW/m . All of these observations confirms the idea that the Gakkel Ridge belongs to oceanic spreading zones with modern volcanism and seismic activity. At the boundary of the shelf the thickness of the lithosphere
2increases of up to 60 km, heat flow values are reduced to 70 mW/m and the seismic activity is decreased. At the edge of the shelf from Franz Josef Land to the South Barents Sea basin the thickness of the lithosphere increases to 80 km, the Moho from 15 to 25 km and the sedimentary layer - up to 10 km. The Moho is dipped up to 35 km. The values of the heat flow are in the range of
260-70 mW/m .In the South Barents Sea basin a background of heat flow is 58-66 mW/m2. Some anomalous
2values are 114 and 196 mW/m (see. Fig. 1) and can be attributed to the influence of exogenous factors, such as bottom currents. In this area, the lithosphere is reduced to 65 km and in some places - up to 35 km. According to (Artyushkov et al. 2014) there were extension blocks of the lithosphere. The result of the thinning of the lithosphere was the emergence of rifts and grabens. Tectonic processes are accompanied by anomalous heat flow of the upper mantle or mantle diapirs. Also magmatism was developed actively at the origin stage of the rift depressions.
The continental part of the cross-sections A-B is characterized by cold lithosphere with thickness more than 200 km, by the continental crust about 40 kilometers and by a relatively thin or missing
2sedimentary layer. The value of the heat flow is reduced to 30-35 mW/m . Weak seismic activities is observed at the boundaries of major tectonic structures.
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ACKNOWLEDGMENTSThis work was supported in part by the Ministry of Education and Science of the Russian Federation (project no. RFMEFI61014X0006)
- sedimentary rocks- basement rocks- upper mantle
2- a plot of heat flow, mW / m- fluid-saturated zone of the unconsolidated sedimentary cover- arrays of basites- arrays of eclogites- the epicenters of seismic events, M – magnitude
M
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- Moho boundary- the boundary of lithosphere and asthenosphere by geothermal data- asthenolith, direction of flow
6.0 <
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- North-Barents Basin- South-Barents Basin- South-Kara Basin
NBSBSK
Legend:
Introduction
Fig. 3. Map seismicity and active Faults in the Region Nordaustlandet-Bely
A rupture of the Earth's crust can be complete within the rift, which is characteristic for ocean rifts and for transition zones from continent to ocean (basites, eclogites) (Kaschybin et al, 2013). Not all of the Earth's crust dives are characterized by a significant stretch (Artyushkov et al. 2015).
The distribution of the heat flow in the Western Arctic basin correlates with the capacity of sedimentary cover. The figure 4 represented contour depth to basement in the north-western part of the Eurasian continental margin, where there are (10-20 km) depressions in the Barents-Kara region: SB- South - Barents Sea, NB - North Barents Sea, SK - South Kara (Kaschybin et al, 2011). This data confirms the connection of high heat flow with a maximum dipping of the foundation (see Figure 4).
Seismicity, heat flow and tectonics of the West Arctic BasinIrina Basakina (1), Galina Antonovskaya (1), Elena Kremenetskaya (2), Michail Khutorskoy(3).
European Geosciences UnionGeneral Assembly 2016Vienna Austria 17-22 April 2016EGU.eu
The Federal Research Center for Integrated Studies of the Arctic Russian academy of sciences
Heat flow of the Arctic Basin
Seismicity of Arctic region
(1) Institute of Environmental Problems of the North, Ural Branch of RAS, Arkhangelsk, Russian Federation(2) Kola Branch of Geophysical Service, Russian Academy of Sciences, Russian Federation(3) Geological Institute, Russian Academy of Sciences, Moscow, Russian Federation
A significant contribution to the study of seismicity of the Arctic was made possible by the installation of new stations, located directly in the Arctic zone - "Amderma" (AMD), 2010 and the "Franz Josef Land" (ZFI), 2011. A summary map of seismicity based on the data of the Arctic seismic networks for the years 2011-2014 is presented in Fig. 2.
The continental part of the Eurasian plate is characterized by low seismicity. Significant seismic activity occurs in the north of the Barents Sea shelf (Fig. 4), which is characterized by low thickness of lithosphere (35 km) and considerable fragmentation of the continental slope. There is clear evidence that epicenters of earthquakes are confined to the rift valleys. Note that anomalously high heat flow values also are confined to rift structures on North of the Barents Sea. However, spatial coincidence of the anomalies of heat flow and epicenters is unlikely because of high temperature of the lithosphere and its lower viscosity. This, in particular, can explain an absence of seismicity in Orly trough within the Svalbard plate and some seismic activity on the continental slope.
An interesting area for the investigation of intraplate seismicity is the Svalbard archipelago. The tectonic setting of this area is unique in that an active spreading ridge (the Knipovich Ridge) lies very near the passive continental margin, and also because the archipelago, as well as the surrounding oceanic areas have a very complex tectonic history.
To the west of Svalbard we have the Mid-Atlantic spreading ridge with constant high earthquake activity. To the South-East, is the Storfjorden area which has recently experienced a significant increase in seismic activity. Thus an earthquake of magnitude 6 which occurred on 22 February 2008 was the largest earthquake in the North Atlantic for last 100 years, and was followed by thousands of aftershocks, which continued for more than five years (Pirli et al., 2010). In general, we observe ongoing earthquake activity in most regions of the Svalbard archipelago.
