Seismological studies at the Sodankylä Geophysical Observatory: from lithosperic studies to polar seismology

Elena Kozlovskaya 2008

Sodankylä Geophysical Observatory of the University of Oulu (SGO) is located at 67°22' N, 26°38' E in the middle of Finnish Lapland. It was established in 1913 and since then has gained a long experience in carrying out multidisciplinary geophysical observations in polar region. Seismological observations at the University of Oulu and SGO have been carried out since 1965. At the moment it operates Northern Finland Seismological Network (FN) consisting of five permanent seismic stations; four of which are equipped by broadband 3-component STS-2 seismometers. Real-time data from stations is transferred via Internet to the data center in Oulu and to the GEOFON data archive at the GeoForschungZentrumPotsdam (Germany). Sodankylä Geophysical Observatory has own pool of portable seismic recording instruments. With these instruments, seismological group of the SGO has participated in many international seismic projects devoted to studies of the continental lithosphere. Since 2007, the seismological group of the Observatory participates in the POLENET (Polar Earth Observing Network) project that is an international multidisciplinary geophysical research in polar regions (both Arctic and Antarctic) during the International Polar Year 2007-2009. A part of the POLENET scientific program is POLENET/LAPNET—a temporary seismic array research in northern Fennoscandia. The Observatory is a leading organisation of the POLENET/LAPNET project.

Deep structure of the crust and upper mantle of the northern, mainly Archaean part of the Fennoscandian shield, is poorly known, as the number of permanent seismic stations and controlled-source seismic profiles there has been always significantly lower compared to its southwestern part. However, even these rare studies showed that the upper mantle there is heterogeneous and seismically anisotropic. In order improve this knowledge, a temporary seismic array was deployed there during May and September, 2007. The array consists of 33 temporary stations and permanent broadband stations in northern Finland, Sweden, Norway and Russia. The array will record teleseismic, regional and local events during 2007-2009. As most of the stations of the array are located beyond the polar circle, operation of broadband instruments in extreme polar climate conditions is a challenging task. The research aims to obtain a 3D seismic model of the crust and upper mantle down to 670 km (P- and S-wave velocity models, position of major boundaries in the crust and upper mantle and estimates of seismic anisotropy strength and orientation) in northern Fennoscandian Shield. The 3-D model can be used also to define spatial distribution and depth of the Archean lithosphere below Finland for the purpose of mineral exploration. The project will contribute to the POLENET research program by collecting waveforms of seismic events traveling through the deep Earth (in particular, the Earth's core) and glacial seismic events in Arctic regions. An important part of the LAPNET project is study of regional and local seismic events. In northern Fennoscandia, local seismic events are quarry blasts and weak earthquakes originating from re-activated ancient fault zones. These events can be used to create a 3-D velocity model of the crust, which is a necessary constraint in all studies using waves from teleseismic events. The 3-D model of the crust and upper mantle will be also used to improve registration and location of local earthquakes and understanding of mechanisms of local seismicity in northern Fennoscandia.