Norwegian National Seismic Network

The seismograph installed in the Bergen Museum in 1905, marked the initiation of the Norwegian National Seismic Network (NNSN). Since then, there has been several single stations, small local networks and arrays (seismic antennas) in operation. From 1992, all stations except the NORSAR (Norwegian Seismic Array) arrays, were joined in the national network. The Norwegian oil industry has supported the operation of seismic stations at UiB since 1984. NNSN is today financed by the University of Bergen and the Norwegian Oil Industry Association and the operation takes place at Department of Earth Science, the University of Bergen.

Seismic stations in Norway in time. From the top: black lines indicate stations in Bergen, thin red lines are other UiB stations, heavy red are NORSAR arrays and thin brown and black are time limited local network operated by both UiB and NORSAR. Abbreviations: WWSSN: World Wide Standardized Seismic Network. NORESS, ARCESS and SVAESS are NORSAR arrays.

Norwegian National Seismic Network (NNSN) and other seismic stations in Norway. Blue symbols are NNSN stations, and red are NORSAR arrays. Station JMIC is operated by NORSAR.

Typical NNSN station

One or more seismometers are placed outside the house in order to avoid noise from the building. From the seismometer a cable (�Kabel�) leads to the registration unit (�Registreringsenhet�), which is typically an analog to digital converter and a PC. From the PC, the data is transmitted to UiB using Internet.

Typical sensor installation

It is important that the seismometer is installed with contact to solid rock in order to avoid vibration noise from the uppermost soil layers. A typical NNSN station consists of a plastic tube cemented to the rock, and attached with iron bars. The installation is underground to avoid wind noise. This type of installation is used for measurement of signal down to 0.2 Hz and is well suited to detect Norwegian earthquakes.

Seismic stations on Jan Mayen

Jan Mayen is our outpost in the Norwegian Sea. There we find Beerenberg, the only active volcano in Norway, and also the largest earthquakes. The data from Jan Mayen are transmitted via satellite so that Beerenberg can be monitored continually.

The station near Beerenberg gets electricity from a windmill and a solar panel. The seismometer is installed in the yellow box to the right. Data is sent by radio to the central base on Jan Mayen.

Broadband stations used by NNSN

Broadband stations are particularly well suited to register earthquakes from the entire world. They must be able to register very low frequencies, down to 0.001 Hz, which is the same as an oscillation with a period of 1000 seconds. This requires very stable temperatures and there are special demands on the installation. There are 5 broadband stations in NNSN.

The station in Ny �lesund, Svalbard. On the photo to the right the entrance to the station is shown, and to the left a schematic figure. The seismometer is placed in the lower room to minimize the influence of pressure and temperature variations.

The station in Kongsberg old silver mine. This is one of the best stations in the world due to its location deep in a mine.

Flow of data in NNSN

• Data is received from NNSN stations 24 hours a day
• Processed data are received from NORSAR and international data centers every day
• All Norwegian data and selected foreign data are processed together (calculate location and magnitude) and stored in a data base at UiB
• All data are available to the public and are also sent to international data centers.

NNSN and the public

NNSN is continually updating information about Norwegian earthquakes on our web page. The map shows events from the last 10 days.

In case of felt earthquakes, NNSN will collect Information from the public, manually and through the institute web page.

NNSN has a 24-hour telephone service where the public can get information about earthquakes. Office hours: 55 58 34 10, 55 58 36 00, outside office hours 55 14 00 98, 55 12 27 23 or 55 93 70 73

Use of data

• General information to the public about recent events; earthquakes or other events.
• Examples of other events than earthquakes are explosions, ship groundings (Rocknes), accidents (the Sleipner platform which sank), induced earthquakes (Ekofisk), or land slides.
• Seismic hazard: data from NNSN have been particularly important for offshore oil installations.
• Research

Rocknes accident

In connection with the Rocknes accident on January 19th 2004, the NNSN stations around Bergen registered an unusual signal. The seismograms show the registration of the strongest shaking at the stations: ASK: Ask�y, BER: University of Bergen, EGD: Espegrend and RUND: Rundemannen. First time marking is at 15:32:10 GMT (16:32:10 local time). The time scale is seconds.