When a seismic event has occurred and has been registered by the LKAB seismic system a mining engineer firstly completes a preliminary analysis of the event. Brief information via sms and e-mail is forwarded to the responsible and affected individuals internally within LKAB and externally to for example the municipality and the County Administrative Board.
An analysis of the event is prepared and a written report is created for events that have been sufficiently large to have activated vibration meters, which are placed in the community, at levels that are assessed to be noticeable or for events noticed by many individuals who have therefore contacted LKAB for information.
The report is distributed to responsible individuals at LKAB as well as externally to the municipality's rescue service, the municipal management as well as affected authorities such as the County Administrative Board. Information is also posted on the web (only in Swedish).
It might take a few hours before exact answers are given depending on where the seismic event took place, what time of day or night it happened and how much information must be gathered.
Large-scale mining for ore in underground mines can lead to seismic activities. This means quaking or tremors occur in the bedrock. LKAB monitors the activity in its mines in Kiruna and Malmberget, and works to reduce these tremors.
Seismic events occur when the natural tension in the bedrock changes. The greatest rock stress is horizontal – lateral – rather than vertical, i.e. top-to-bottom as we might expect. When iron ore mining in the underground mines continues deeper and 'cuts off' the bedrock, the stress must find new ways around and under the extracted ore. Stress concentrations are formed, and if the stress is greater than the strength of the rock mass, the rock will give, i.e. fracture. Seismic activity is the rapid fracture of a rock mass that releases a lot of energy. The majority of such events near LKAB mines – sometimes several hundred to a thousand a day – are so minor that they cannot be felt and are only measurable with sensitive instruments. Sometimes though, energy builds up and is released in larger tremors that are felt in the communities closest to the mines.
LKAB posts information in Swedish on its website in connection with major seismic events stating the time, location, magnitude and the biggest vibration. It may take an hour or two as the readings from the instruments must first be collected and checked. We also send a report to the civil authorities.
Do you have any questions or concerns about seismic events? If so, email firstname.lastname@example.org or send a letter to LKAB, Information Dept., SE-981 86 Kiruna, SWEDEN.