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Arctic
Environmental Research
Arctic Environmental Research 19(1): 11-19 UDC 550.34.06 DOI 10.3897/issn2541-8416.2019.19.1.11
Updated data on the current seismicity of the White Sea and the Karelian region during the period 2005-2016
YaV Konechnaya1,2, AN Morozov1,3, NV Vaganova2, IA Zueva4
1 Geophysical Survey of Russian Academy of Sciences (Arkhangelsk, Russian Federation)
2 N. Laverov Federal Center for Integrated Arctic Research (Arkhangelsk, Russian Federation)
3 N. Laverov Federal Center for Integrated Arctic Research (Obninsk, Russian Federation)
4 Institute of Geology Karelian Research Center of Russian Academy of Sciences (Petrozavodsk, Russian Federation) Corresponding author: Yana Konechnaya ([email protected])
Academic editor: AleksandrI. Malov ♦ Received 7 February 2019 ♦ Accepted 15 February 2019 ♦ Published 8 March 2019
Citation: Konechnaya YaV, Morozov AN, Vaganova NV, Zueva IA (2019) Updated data on the current seismicity of the White Sea and the Karelian region during the period 2005-2016. Arctic Environmental Research 19(1): 11-19. https://doi.org/10.3897/issn2541-8416.2019.19.1.11
This article is the result of previous studies to clarify the seismicity of the White sea, supplemented by similar studies on the continental part of the Republic of Karelia. The relocated catalog of earthquakes was created for the period from 2005 to 2016 for White Sea and the Karelian region. With the help of proven methods, the parameters of the epicenters of identified earthquakes were relocated and a map of current seismicity was obtained. The parameters of the epicenters were specified using BARENTS travel-time model, a single methodological approach (using Generalized beamforming) and all currently available source data and bulletins of Russian and foreign seismic stations. The obtained seismic catalog allowed us to identify the main patterns of the distribution of current seismicity in the White Sea region. Seismicity of the White sea and the Karelian region is characterized as low-magnitude (generally of low magnitude with ML<2.0). Most earthquakes in the White Sea are characterized by a focal depths up to 20 km. Analysis of catalog shows that the majority of earthquakes are concentrated in the north-western part of the defined area, in the continental part of Karelia and Kandalaksha graben. Some earthquakes were recorded in the eastern and central part of the White sea.
Keywords
Current seismicity, earthquake, seismic network, epicenter, map, White Sea
Abstract
Copyright Konechnaya YaV et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Introduction
The White Sea area, which includes the White Sea water area and surrounding areas of the Republic of Karelia, is one of the most fragmented, movable and active regions throughout the entire Eastern European platform. Distinct tracks of paleoearthquakes were encountered in all major parts of the White Sea region in the Kandalaksha, Dvina, and Onega bays, as well as in the Gorlo Belogo Morya area (Nikonov and Shvarev 2013).
The data for the historical and instrumental period of observation indicate an increased seismic activity in the western part of the region, especially in the Kandalaksha graben area, the main active structure of the White Sea (Nikonov 2004; Assinovskaya 2004). The particular interest are present adjacent plots, which are located responsible objects and conducting active mining operations. With the development of seismic networks in the Karelia region (Sharov et al. 2007), in the Murmansk and Arkhangelsk regions (Yudakhin and Frantsuzova 2006) in the 1990s and 2000s, the area of the White Sea has been the highest density of seismometric observations since 2004. In addition, events from the considered region are recorded by stations in Finland, Sweden and Norway and data about them contained in the catalogs of foreign seismological services.
However, no common data processing of available seismic data has been carried out yet. Thus, the most important problem was the joint processing of all available seismological data using a unified velocity model and calculation algorithm. It allows to determine the parameters of earthquake hypocenters based on seismic stations located in wide azimuth and epicentre ranges, and to obtain high precision of earthquake hypocenter location. In addition, some studies have already been successfully carried out on parts of the White Sea (Morozov et al. 2019) and are now supplemented by data from the western part of the White Sea - the territory of the Karelia Republic, which is also characterized by seismicity (Sharov et al. 2007). The boundaries of the study area are shown in Fig. 1.
Materials and methods
The receipt of the specified catalog was completed in several phases.
1 phase
Based on data from the Institute of Seismology of the University of Helsinki (Finland) (Institute of
Fig. 1. Seismic networks of Finland, Sweden, Norway and Russia, which monitor seismic events occurring in the White Sea region. Dotted line covers study area
Seismology), the preliminary catalog of the earthquake in the area of the White Sea during the period from 2005 to 2016 was compiled. The advantage of the catalog (Institute of Seismology) is not only the presence of low-magnitude events, but also a note about the expected nature of the event (earthquake or explosion) that in the first stage enabled the exclusion of career blasts from bulletin creation. Event selection was performed within the range of the considered area (Fig. 1). During 2005-2016 period in the preliminary catalog, 66 earthquakes with magnitude ML (HE) values of 0.4 to 2.4 were selected. In addition, only three earthquakes have a value greater than 2.0. This again confirms the views and opinions of modern researchers on the predominantly weak regional seismicity (Sharov et al. 2007; Assinovskaya 2004).
2 phase
For each earthquake from the preliminary catalog, a summary bulletin was compiled with the times of seismic phases
Bulletins were compiled based on data from following seismic stations of several networks:
- the Federal Center of Multidisciplinary Studies of the Arctic of the Russian Academy of Sciences (RAS) (the network code is AH);
- the Geological Institute of the Karelian Research Center (RAS);
- the Kola Branch of the RAS Unified Geophysical Survey Federal Research Center or UGS FRS (the network code is KOGSR);
- the Central Department of the RAS Unified Geophysical Survey Federal Research Center (the network code is OBGSR);
- the Institute of Seismology at the University of Helsinki, Finland (the network code is HE);
- the Sodankyla Geophysical Observatory at the University of Oulu, Finland (the network code is FN);
- the NORSAR Agency, Norway (the network code is NO)
- the Norwegian National Seismic Network, University of Bergen, Norway (the network code is NS).
Should be noted that data from domestic stations (seismic networks AH, KOGSR, OBGSR and RAS) have been supplemented for 34 events from the preliminary catalog. The location of the seismic stations data of which appear in the bulletins and will be taken in further processing is shown in Fig. 1.
3 phase
Since open pit mining operations are actively conducted in considered region, further studies have been carried out to determine the nature of the events from the preliminary catalog. All events were verified by the recognition criteria (Asming and Kremenets-kaya 2002), developed at the Kola branch of FITS EGS RAS. As a result, 3 events identified as explosions were excluded from the list. The completed catalog with predetermined hypocenters contains 63 earthquakes.
4 phase
The redefinition of hypocenter parameters based on summary bulletin was carried out by using the Generalized beamforming method (Ringdal and Kv^rna 1989) in an improved form implemented in the NAS program (Asming et al. 2017; Asming and Prokudina 2016). The algorithm for calculating hypocenters is described in details according to (Morozov et al. 2019).
Previous studies have shown (Morozov et al. 2019) that using the advanced algorithm implemented in the NAS program in conjunction with the rapid BARENTS model provides relatively accurate hypocenter parameters and allows the use of this technique to recalculate all subsequent earthquakes in the White Sea region. The resulting redefinition of hypocentres does not differ fundamentally from the catalog of the Institute of Seismology in Helsinki, despite the extensive use of other additional data.
Results
The main results of the study consist in creation of an updated catalog and mapping of a modern seismicity according to the Table 1 and Fig. 2.
Table 1. The catalog of revised hypocenter parameters for the earthquakes recorded in the White Sea and the Karelian region for the period 2005-2016
Date
Origin time
Hypocenter parameters
Month Day Hour Minute Second h, km
Error ellipse Calculation parameters
AzMajor, Rminor, Rmajkm Nstations/ Range of Azimutal ML
Magnitude
° km Nphases distance, km angle,° (HE)
1 2005 2 16 6 48 31.2 67.41 32.05 16, 6-32 150 4 5.1 10/17 48-814 97 1.7
2 2005 3 18 1 49 43.7 67.14 31.91 3, 0-17 140 5 8.4 6/10 70-789 121 1.1
3 2005 5 17 2 44 11.6 66.98 31.27 20, 0-99 140 2.9 7 4/7 100-209 175 1.3
4 2005 8 22 2 42 41.2 66.39 30.8 10, 4-16 90 4.3 7.4 6/11 52-293 267 0.8
5 2005 10 1 1 22 59.1 67.24 32.54 10, 0-24 120 4.2 7.9 10/16 47-583 143 1.6
6 2005 10 19 3 15 44.6 66.88 31 8, 0-22 90 4.6 10.7 5/8 80-195 275 1.2
7 2005 10 22 17 46 44.8 64.49 40.95 0, 0-13 70 10.4 14.5 11/22 24-1020 235 2.8
8 2005 10 23 0 34 6.3 66.64 33.29 16, 0-51 100 5.6 11.8 12/21 107-639 200 1.6
9 2005 12 2 0 3 57.7 66.89 31.36 15, 8-22 110 2.7 4.8 10/20 97-382 140 1.6
10 2005 12 12 1 46 3.8 66.87 31.02 14, 5-22 120 2.9 5.4 10/15 84-441 133 1.2
11 2006 1 13 21 35 1.3 66.64 31.09 0, 0-2 130 1.9 5.5 7/11 72-291 174 0.9
12 2006 2 2 12 29 10.8 66.59 29.3 5, 0-99 60 3.8 9.8 4/8 27-287 205 1.1
13 2006 2 18 8 10 2.8 66.84 32.44 0, 0-13 120 4 10.1 10/18 88-632 189 1.7
14 2006 3 30 10 46 2.1 70.68 52.88 35, 0-99 110 19 40 13/19 836-1555 272 2.6
15 2006 4 4 1 47 2.6 66.28 31.01 3, 0-10 130 2.9 4.8 11/19 64-423 148 1.1
16 2006 4 13 13 25 14.2 66.72 29.33 11, 0-21 100 3 5.1 8/12 37-354 113 1
17 2006 7 11 18 24 41.9 67.31 32.27 10, 0-27 120 4.3 6.6 15/27 45-715 149 2.1
18 2006 7 23 1 32 8.8 66 39.58 29, 2-99 60 7.3 10.9 19/33 218-1036 192 2.3
19 2006 10 25 12 24 42.7 66.94 31.07 10, 0-33 130 2.6 12.9 5/7 91-144 175 0.7
20 2006 12 31 5 35 56 65.66 32.02 0, 0-3 60 4.2 11.2 7/10 104-313 235 0.5
21 2007 3 13 14 31 28.6 66.29 31.16 2, 18-30 130 2.9 5.5 18/30 63-549 146 1.9
22 2007 3 29 22 53 21.9 66.15 30.54 0, 0-5 90 2.8 5.8 9/14 28-240 264 0.8
23 2007 4 8 14 35 13.7 66.15 33.09 5, 0-15 120 3.6 7.1 13/23 142-625 189 2.4
24 2007 8 1 4 31 57.1 66.58 31.28 10, 2-18 130 2.1 5.1 8/16 78-226 183 1.3
25 2007 8 3 0 59 38.4 66.02 30.36 18, 15-22 90 2.6 5 7/12 16-227 258 0.4
26 2007 8 19 22 56 3.3 69.64 33.1 33, 3-98 40 6.3 12.7 29/56 226-1377 242 3
27 2007 9 11 8 4 48.7 69.73 29.99 0, 0-99 40 6.6 20.9 4/6 108-406 268 1.3
28 2007 10 30 0 19 16 66.63 30.91 20, 0-99 100 2.7 9.2 4/6 60-135 238 0.5
29 2007 11 23 4 22 30.3 66.3 32.75 0, 0-10 120 3.4 7.7 11/20 130-596 219 1.4
30 2008 1 27 1 54 25.5 68.19 29.74 8, 0-14 40 2.5 3.4 9/16 48-254 143 1.6
31 2008 1 27 3 24 23.8 68.18 29.76 12, 0-27 30 3 3.9 5/9 49-228 143 1.2
32 2008 5 10 15 5 8.4 66.86 31.77 6, 0-14 110 2.9 5.5 16/28 98-531 151 1.6
33 2008 6 22 18 1 41.2 68.19 30.79 16, 8-23 60 3.6 5 12/21 70-298 164 1.3
34 2008 7 12 17 17 14.8 68.39 35.78 25, 12-52 60 7.4 10.8 14/22 135-856 227 2.7
35 2008 9 12 20 14 25.6 68.72 33.29 15, 0-65 70 6.8 18 7/9 185-331 248 1.2
36 2008 10 19 23 29 10 66.87 29.16 6, 0-23 70 1.4 2.7 9/18 58-146 149 0.5
37 2008 10 25 3 9 45.3 66.54 32.42 0, 0-7 120 2.9 7.2 11/20 122-422 220 1.3
38 2009 5 25 20 58 4.3 67 31.77 7, 0-21 80 4.6 10 8/12 171-455 213 1.1
39 2009 8 31 15 17 50.8 66.31 31.05 28, 22-33 110 3.3 6.1 16/30 62-548 183 1.5
40 2009 9 8 0 23 48.3 66.78 31.13 18, 11-24 100 3 4.1 21/38 81-777 82 2.1
41 2009 9 8 4 42 16.9 66.79 31.08 14, 8-22 110 2.5 5.6 11/18 79-383 168 1.4
42 2009 11 16 4 27 26.6 66.04 30.03 7, 3-10 110 2.4 4.7 20/37 5.5-495 167 1.6
43 2009 11 28 14 32 23.6 66.26 33 1, 0-13 100 3.6 4.6 10/16 138-315 167 1.6
44 2009 12 3 19 55 45 66.35 31.28 13, 7-21 100 3.5 6.1 9/16 70-236 247 0.8
45 2009 12 11 23 53 52 67.08 31.8 11, 3-18 120 2.4 4.7 11/20 78-376 171 1.2
46 2010 2 25 1 42 13.8 66.43 30.53 0, 0-7 90 2.2 4.7 10/17 40-254 220 0.7
47 2010 3 27 23 6 55.8 66.24 32.02 18, 1-24 170 7.4 12.9 6/10 93-180 333 0.7
48 2010 4 6 4 49 3.4 66.9 31.08 6, 0-12 110 1.9 3.5 12/23 87-358 159 1.3
49 2010 5 20 1 33 48.3 66.31 32.12 25, 16-34 30 7.9 8.5 6/11 98-268 316 0.7
50 2010 9 5 5 17 33.2 66.2 30.74 2, 0-7 130 2.8 5.2 17/29 42-529 176 1.4
51 2011 1 20 14 37 0 65.35 30.54 10, 2-16 60 2.3 4 10/17 52-273 123 0.9
52 2011 6 16 15 44 6.5 66.59 31.58 0, 0-5 100 4.5 9.4 9/15 89-523 214 1.6
53 2011 8 13 11 54 52.2 66.18 34.23 0, 0-48 120 6.4 12.1 6/11 173-272 272 1.2
54 2011 10 11 20 4 59.4 66.45 30.68 20, 15-25 110 3 4.9 14/22 47-404 138 1.2
55 2011 11 15 17 48 10.2 67.43 31.73 0, 0-4 140 2.5 3.4 11/20 58-345 131 1.5
56 2012 1 3 0 1 37.9 68.14 29.3 0, 0-99 70 3.4 6 4/8 44-220 206 1.1
57 2012 1 8 20 54 25 66.81 31.46 0, 0-6 110 3.1 5.5 19/30 99-606 145 0.7
2.9
1.9
ML
ML
Date Origin time
Month Day Hour Minute Second
Hypocenter parameters 9»° h, km
Error ellipse
Calculation parameters
AzMajor,
Rminor, km
Rmajkm
Nstations/ Nphases
Range of distance, km
Azimutal angle,°
Magnitude
ML ML ML (HE) (KOGSR) (AH)
58 2012 2 15 6 48 8.7 66.46 32.09 4, 0-22 110 5.2 16.4 7/10 100-428 272 1.2
59 2012 3 27 7 13 12.5 66.11 30.36 8, 3-13 90 2.3 2.7 10/19 22-271 136 0.9
60 2012 4 22 20 9 32.4 67.01 31.32 6, 0-13 110 2.3 3.3 12/23 97-242 107 1.3
61 2012 4 30 8 48 27.4 65.78 30.8 0, 0-12 100 2.2 3.6 6/10 45-128 288 0.8
62 2012 8 27 7 29 45.3 66.16 30.77 12, 7-18 100 2.9 6 7/12 36-285 236 1
63 2012 10 7 3 43 12.9 66.21 47.84 26, 99 50 8.6 19 13/25 526-1656 170 1.6
64 2012 10 11 15 0 48 65.82 30.35 25, 19-30 100 1.9 3.9 5/9 27-92 262 0.5
65 2012 12 4 7 13 9 65.89 30.15 5, 1-8 100 2.7 5.8 11/19 19-263 217 1.1
66 2013 3 28 7 2 16.5 63.97 41.5 21, 8-36 150 6.8 8.1 31/59 82-2596 83 2.9 3.4
67 2013 4 3 14 49 35 66.99 30.19 0, 0-6 100 2.3 3.6 16/28 74-383 128 1.5
68 2013 4 26 19 51 8.2 68.04 29.37 6, 0-13 70 3.3 6.3 7/12 32-230 188 0.7
69 2013 5 1 22 52 21.7 66.49 30.79 22, 15-29 120 2.2 4.5 10/18 54-395 172 1.3
70 2013 11 26 20 39 7.1 66.44 30.85 15, 11-22 80 4 6.9 7/12 57-217 269 0.5
71 2013 11 30 22 16 20.1 65.48 31.73 15, 0-59 20 6.2 9.1 6/8 105-656 142 0.8
72 2014 2 25 18 53 6.1 66.43 32.46 1, 0-10 120 2.6 3.7 12/21 122-431 118 1.7
73 2014 3 20 13 56 40.7 64.87 35.52 41, 29-57 50 6.3 8.2 13/23 25-543 128 1.2
74 2014 4 8 0 45 38.6 65.98 31.39 0, 0-2 110 3.4 5.7 7/13 63-246 263 0.6
75 2014 8 20 2 27 38 66.3 31.83 4, 0-12 120 2.9 3.6 10/17 92-337 115 1.3
76 2014 8 29 23 37 39.2 66.6 31.56 1, 0-8 100 3.4 8.5 7/13 88-241 263 0.9
77 2014 9 5 2 27 28.3 66.44 31.7 3, 0-10 90 3 4.1 9/15 92-320 121 0.8 1.2
78 2014 9 8 4 15 11.7 67.96 30.17 3, 0-11 10 2.8 3.1 6/11 33-256 138 1
79 2014 9 12 22 9 43.3 66.32 31.51 26, 15-32 110 4 8.5 5/9 71-155 273 0.6
80 2014 10 2 12 19 23.1 66.4 32.53 0, 0-7 120 3 4.3 14/23 123-508 119 1.4
81 2014 10 11 0 32 45.6 65.94 32.43 0, 0-4 100 5.6 10.1 6/8 114-309 243 0.9
82 2014 11 23 23 20 11.6 66.5 31.53 9, 0-21 100 3.4 6.8 6/11 86-170 251 1.1
83 2014 11 30 9 43 19.9 67.15 32.53 13, 2-25 140 3.6 6.4 8/12 57-393 178 0.7
84 2014 12 13 21 10 40.1 66.28 31.18 21, 15-27 110 3.1 4.9 11/17 62-307 164 1.2
85 2015 1 8 6 20 41.2 66.17 29.96 19, 16-25 90 1.9 3.3 5/8 15-95 227 0.1
86 2015 2 15 3 0 35.9 65.95 30.07 9, 0-15 100 1.3 2.8 6/10 Dec-88 234 0.3
87 2015 2 28 19 33 49.1 66.31 31.85 0, 0-14 130 2.4 6.6 6/10 92-260 233 1.1 1.5
88 2015 3 20 14 46 38.3 60.29 43.89 0, 0-99 150 10 22.8 17/29 177-1054 235 2.7
89 2015 4 2 8 16 56.6 68.31 29.17 0, 0-7 50 3.1 4.6 8/14 65-819 126 1
90 2015 4 4 20 23 38.9 66.17 30.74 5, 0-12 110 4.2 10.2 5/8 39-286 263 0.6
91 2015 4 22 2 8 54.7 66.95 31.1 0, 0-6 100 2.5 4.8 9/15 89-220 161 0.7
92 2015 5 10 14 3 11.7 66.74 31.13 21, 15-25 130 2.2 3.6 14/25 80-334 82 1.4
93 2015 5 31 0 40 34.5 66.68 33.21 0, 0-8 130 3.8 9.6 8/11 104-317 222 0.8
94 2015 6 23 6 15 59.3 66.88 31.03 13, 6-21 100 2.5 4.5 10/16 84-219 153 1
95 2015 6 26 3 45 48.9 66.57 32.03 23,13-29 120 2.7 5.2 8/13 112-264 163 0.7 1.7
96 2015 6 29 13 5 9.1 65.93 31.88 19, 14-23 110 2.5 3 18/31 89-512 112 1.9 2.3
97 2015 7 6 17 31 34.8 66.39 31.83 15, 7-23 110 3.4 4 10/18 94-560 115 1.7 2
98 2015 7 12 11 31 57.2 66.45 31.42 10, 5-15 100 3 5.8 9/17 80-237 249 0.8
99 2015 8 1 4 31 4.4 66.21 30.55 13, 8-20 90 2 3.8 7/12 32-178 226 0.7
100 2015 9 11 19 23 52.2 66.36 31.33 20, 16-26 110 2.4 3 27/50 74-868 59 2.4
101 2016 1 12 19 14 50.2 66.96 29.76 14, 0-32 80 1.9 4.8 5/8 66-147 181 0.4
102 2016 2 28 17 48 7 67 32.01 16, 8-23 110 2.7 3.9 24/43 79-771 57 1.8 2.1
103 2016 4 3 0 4 27 67.52 32.09 0, 0-6 160 3.3 4.9 7/13 40-282 152 1 1.5
104 2016 4 23 0 9 24.9 67.63 33.31 13, 3-19 170 3.9 8.4 10/15 16-493 106 1.4
105 2016 5 17 11 13 19.4 66.9 30.16 1, 0-6 90 2.6 4 17/32 98-380 121 1.5
106 2016 5 26 4 46 0.7 66.04 35.66 34, 2-99 90 5.8 12.5 10/18 197-436 242 1.1 2
107 2016 6 13 6 16 9.2 69.58 33.78 24, 14-32 30 4 8.5 11/17 64-476 196 2.1
108 2016 6 19 22 33 25.4 67.05 30.05 5, 0-12 90 2.7 3.7 19/32 79-388 114 1.5
109 2016 7 9 17 38 20 67.22 32.3 10, 0-29 140 3.7 6.9 10/15 53-399 168 0.8 1.3
110 2016 7 30 21 42 24.5 66.45 32.94 3, 0-13 120 3 5.5 17/29 113-573 167 1.5 1.9
111 2016 8 3 15 49 55.4 66.35 30.68 14, 10-18 110 2.9 3.6 21/32 49-749 89 1.6
112 2016 8 7 19 42 11.2 66.35 31.49 20, 10-29 130 3.8 5.1 10/15 83-726 119 1.1
113 2016 9 15 8 13 2.6 66.88 30.94 23, 18-28 100 2.7 3.4 23/43 83-705 76 2
114 2016 11 15 19 20 23.7 65.64 30.16 7, 1-12 80 2.5 5.6 8/12 45-236 180 0.7
115 2016 11 19 20 47 20.3 66.75 32.47 4, 0-15 120 2.7 5.3 11/18 99-404 168 1.1 1.5
116 2016 11 20 18 21 0.1 66.98 31.44 20, 12-24 110 2.3 3.4 13/23 96-375 135 1.6 1.7
28° 30° 32° 34" 36" 38° 40° 42?
Fig. 2. A map showing revised earthquake epicenters for the White Sea region. The legend on the right shows earthquake classes arranged over depth of focus (H) and magnitude (circle size)
Map analysis Fig. 2 shows that the majority of earthquakes are concentrated in the north-western part of the defined area, in the continental part of Karelia region. The modern seismicity of the White Sea is reflected in the form of a small magnitude. The distribution of the epicenters of recorded earthquakes fully corresponds to the regularities previously revealed in the studies (Assinovskaya 2004;
Nikonov and Shvarev 2013), namely, increased
seismic activity in the western part of the basin and weak seismic activity in the eastern and central parts (Fig. 2).
Discussion
According to fig.2 in the eastern part of the region two earthquakes were recorded in the White-Sea-Dvina area in 2005 and 2013 years where is also an earthquake in the Gorlo Strait area in 2006 year. All earthquakes have a magnitude value of ML (HE) above 2.0, which distinguishes them from other earthquakes. The earthquake of 2005, viewed alongside the earthquake information of 1847 and 1935, as well as the earthquake in 1970 and 1975 (Nikonov 2013). may indicate seismic activity in the White Sea-Dvina region.
Fig. 3. A morphostructural map of the seafloor and coasts of the Kandalaksha Gulf made by S.V. Shvarev using a digital elevationmodel; seismicity is shown for comparison. The legend on the right gives a classification of the earthquakes over depth of focus (H) and magnitude (circle size)
The epicenter of the earthquake in 2013 (Fig. 2) is timed to the fault limiting Arkhangelsk scarp and the Onega-Kandalaksha ancient rift. The focal mechanism of this earthquake calculated in study (Morozov et al. 2016) is fully in line with the conclusions of L.A. Sim (Sim et al. 2011) on regional submeridional compression and sublatitudinal tension characteristic of the eastern part of the Baltic shield.
The epicenter of the 2006 earthquake in the Gorlo Strait (Fig. 2) almost coincides with the epicentre of the historic earthquake of 1912 (Nikonov 2000). In the central part of the White Sea region weak earthquakes over the past ten years are not recorded, as well as for the entire instrumental observation period (Assinovskaya 2004).
The obtained depth values indicate the presence of crustal earthquakes, and in the classification of seismic
events by depth refers to a small-focus ones. Most earthquakes in the White Sea are characterized by a focal depths up to 20 km. For three earthquakes, the epicenters of which are located directly in the waters of the White Sea, and six earthquakes in Karelia, the depths are over 20 km. Earthquakes with a depth of more than 20 km were also recorded in the Arkhangelsk region in 2013.
In the western part of the White Sea region (Fig. 3), most epicenters of small events (22 events) during period 2005-2016 are located outside Kandalaksha graben, but on land to the west and south-west of it, with hypocenters are located at a depth of 5 up to 20 km., respectively. When comparing the epicenter location of the earthquake processed with the map of neotectonic and young morphostructures of Kandalaksha Gulf and its surroundings (first made based on a digital topographic model (Shvarev et al. 2015)
several remarkable correlations can be found (Fig. 3). In the Gulf area, i.e. the Kandalaksha graben itself, especially on its south-west shore, only four events were recorded. The hypocenters were crustal at great distances each other. Their epicenters lie on longitudinal lines running in the direction of the North-West to South-East along the main boundary of the graben.
Conclusion
The results obtained in this article deepen our knowledge about the development of modern seis-micity in the White Sea region. The use of a single speed model, a unified methodological approach and all currently available source data and bulletins of Russian and foreign seismic stations made it pos-
References
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■ Institute of Seismology, University of Helsinki (2019) http:// www.helsinki.fi/geo/seismo/
sible to determine earthquake parameters with the highest confidence.
The results presented in this article confirm the presence of seismicity (generally of low magnitude with ML<2.0) in the areas adjacent to the White Sea. This fact should be taken into account when carrying out the seismic monitoring of the region. The resulting updated catalog consist in essential part of the work carried out to clarify the current seismicity of the entire North of the Eastern European platform and should be included in a single seismic catalog of Eastern European platform, combining earthquakes both in historical and instrumental periods.
The research was supported by the grant RFBR «Modern seismicity of the White Sea region» ( № 18-35-00021).
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