OBF-verkon toiminta ja seismiset havainnot vuonna 2020

This report presents the observatory practice and the observations of the Ostrobothnia local seismic network (OBF) monitoring Fennovoima Oy’s future nuclear power plant site at Hanhikivi, Pyhäjoki, Northern Ostrobothnia, Finland in 2020. The network operated by the Institute of Seismology of the University of Helsinki has been designed to automatically detect and locate low magnitude seismic events, down to ML 0, within 25 km radius from the site. Larger earthquakes are detected and analysed within 50 km radius from the site.

The OBF network consists of 10 seismic stations including a Finnish National Seismic Network permanent station, OUF. The OBF-stations (OBF0, OBF1, OBF2, OBF3, OBF4, OBF5, OBF6, OBF7 andOBF8) were built during 2012 – 2015. The OBF network has been operating as a part of the automatic seismic detection and location routine of the Institute of Seismology since the 1st of June 2013. Detected events have been identifed using spectral methods and their automatic source parameters have been stored in a database. Earthquakes have been revised manually and when possible, focal mechanism solutions have been determined.

During 2020, within 50 km of the Hanhikivi site, altogether 467 explosions were automatically located, 752 false detections were revised, and seven earthquakes (ML -0.4 – 0.3) were detected and analysed. Focal mechanisms of the earthquakes could not be determined as the events were very small. Data coverage of the entire OBF network was 96,6% in 2020 varying between 90,1% and 99,8% depending on the station.