A regional seismic network in northern Norway, SEISNOR, was installed in 1986 and became operational early in 1987. The network consists of six stations with altogether 24 sensors and with interstation distances from 200 to about 1000 km. The stations are independent and remotely accessible. An automated decision system on a central computer polls the stations first for detection information and second for waveform data. Each station has its own detection processor and local disk storage, with capabilities for storing up to 45 hours of recorded data. The system is strongly parameterized, and this has made the data acquisition flexible and easily extendable. The system is robust, and the network has been operated successfully for more than three years.
The SEISNOR network has lowered the detection threshold for events in northern Norway by about 0.7 magnitude units, to about ML 2.7 in the coastal areas and about 3.2 at a distance of 500 km from the coast. This detection threshold is somewhat higher than what one normally should assume based on the station coverage, and the reason for this is that the ambient noise level for the coastal stations is fairly high. For many of the well-recorded events, location precisions are now routinely better than 15 km.