Research Article |
Corresponding author: ER Morozova ( katyasims10@yandex.ru ) Academic editor: Aleksandr I. Malov
© 2019 ER Morozova, AP Turova.
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.
Citation:
Morozova ER, Turova AP (2019) Impact of seasonal variations of ambient seismic noise level on the number of registered earthquakes in the Arctic regions. Arctic Environmental Research 19(3): 123-128. https://doi.org/10.3897/issn2541-8416.2019.19.3.123
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Researchers at the Seismological Laboratory of the Institute of Geodynamics and Geology of the Federal Center for Integrated Arctic Research of the Russian Academy of Sciences (FCIARctic) have been engaged in the seismological monitoring of the European Arctic sector since 2011. In this paper, we present a comparative assessment of the earthquakes spatial distribution in this region based on the data from the International Seismological Centre (ISC) and the FCIARctic’s Arkhangelsk Seismic Network (ASN) obtained in 2012–2016. The paper presents the waveforms of earthquakes occurred at the Gakkel Ridge and the Svalbard archipelago processed with the use of a Russian software package WSG (Windows Seismic Grafer) recommended by the Unified Geophysical Service of the Russian Academy of Sciences. A standard 4–8 Hz bandpass filter was used for the processing of regional Arctic earthquakes. The impact of seasonal variations on the quality of earthquakes registration was analysed based on the seismograms recorded by the ASN’s island-based Arctic stations from 2012 to 2014 The same analysis was done for the central broadband sensor SPA0 of the Norwegian NORSAR-owned SPITS group installed at the Svalbard archipelago. A correlation has been established between the number of earthquakes recorded by the ASN’s island Arctic stations and SPA0 station. The number of regional earthquakes, recorded by ASN’s island Arctic stations is is smaller in summer-autumn periods than in winter periods. Forthe SPA0 station, which is part of SPITS group, there is not seasonality in the number of registered earthquakes. Generally, earthquakes are recorded uniformly, exception on January. This might be due to the increased seismic activity in the Svalbard archipelago during that period.
Svalbard archipelago, seismic station, earthquakes, seismological monitoring
Russia, Norway, Sweden, Finland, Denmark, and Poland are involved in the seismological monitoring of the European Arctic sector. These countries have their seismic stations on the territory of Scandinavia, the Kola Peninsula, the Arctic archipelagos Svalbard, Franz Joseph Land, Severnaya Zemlya, and Greenland. A broad range of data obtained by various seismological services is compiled into a single International Seismological Centre (ISC) catalogue. Since late 2011, the data, collected by Arkhangelsk Seismic Network (ASN) of FCIARctic, is used by the ISC for the global consolidated processing of the earthquakes occurred in the Arctic. Figure
Spatial distribution of earthquakes: a – according to ISC data for 2012–2016 [1] including ASN’s contributions; b – according to data provided solely by ASN for 2012–2017
Figure
The following ASN stations operated in the Arctic region above 70 degrees north: Franz Joseph Land (ZFI), Omega (OMEGA) and Severnaya Zemlya (SVZ) (Fig.
On the Figure
A comparative analysis of the seismic monitoring data presented in Fig.
For the analysis of the impact of seasonal variations on the quality of earthquake registration we compared the ASN island Arctic stations data from 2012–2018 with the data obtained in 2012–2014 by the central broadband sensor SPA0 of the Norwegian NORSAR-owned SPITS group (International Registry of Seismograph Stations), installed in the Svalbard archipelago in 1992. The SPITS group is equipped with broadband seismological equipment; its borehole central sensor SPA0 makes it possible to register earthquakes of different energy classes by the SPITS sensor group. That is way the SPA0 data may be used as reference for the analysis of the operation of the Arctic stations.
The earthquakes were detected and processed with using of the WSG (Windows Seismic Grafer) software package developed by the Geophysical Service of the Russian Academy of Sciences (GS RAS) (
Generally, a record of a regional Arctic earthquake has a typical appearance with a sharp amplitude entry for both longitudinal and transverse waves. Fig.
Earthquake record example from western part of Gakkel Ridge recorded in February and June 2013: 1 – source signal; 2 – signal after bandpass filtering 4–8 Hz
According to (
According to our experience, NORSAR’s seismic catalogues often omit to reflect earthquakes occurred north-east and east of the Svalbard archipelago. This is due to the priorities set by this company. Because of this, we re-processed the SPA0 seismic station records. We analysed the three years (2012–2014) of the station operation and calculated distribution of the earthquakes recorded by SPITS (Fig.
The distribution diagram of the number of earthquakes recorded by the stations in various networks (Fig.
We would like to point out that the processing of ASN island Arctic stations seismic records resulted in an observation that in the summer-autumn period the number of recorded regional earthquakes is less than that in the winter period (Fig.
It is a known fact that earthquakes are the markers of tectonic processes occurring in the Barents-Kara region (Verba et al. 2016). This determines the importance of seismic monitoring in this region. In our opinion, the almost total lack of seasonality in the registration of earthquakes by the SPA0 station (the apparent uniform temporal distribution of earthquakes during the year) is associated with the highest seismic activity of the arch-block rise of the Svalbard archipelago denying the opportunity of the detection of seasonal variations.
In addition, the types of seismic equipment and the quality of itsinstallation also may have an impact on the number of recorded earthquakes. For example, the SPA0 central station of the SPITS group is equipped with a three-component borehole seismometer installed at a depth of 2 m. The entire SPITS group is located away from human settlements.
Due to technical limitations, the ASN (ZFI, OMEGA, and SVZ) equipment was installed at a depth of no more than 80 cm; moreover, the seismic stations themselves are located near anthropogenic noise sources. This ultimately affects the number of recorded events. The principles and issues of the installation of ASN Arctic stations have been described in detail by
The study suggested that the seasonal variations of ambient seismic noise level registered by the ASN stations, caused by technological factors, namely – the difficulty of subtracting an event against a background of anthropogenic noise, rather than natural causes. Installing seismic arrays instead of single stations is a solution that increases sensitivity of each registration point; in addition, it would be advisable to attempt reproducing the Norwegian success in installing seismic stations in the Arctic. We would also like to point out that putting the ASN Arctic stations in operation resulted in new data received on the seismicity of the entire Arctic region and the Barents-Kara area in particular.
We would like to thank the staff of the Seismological Laboratory for making themselves available for consultations during the study. The authors are especially grateful to G. N. Antonovskaya for valuable advice and recommendations during the publication process.
This study was partially supported by the research project funding of the Seismological Laboratory, state registration number AAAA-A18-118012490072-7.