The most severe earthquake likely to hit Groningen province in the coming years will be 4.5 on the Richter scale, not 5 as earlier forecast, according to a confidential new report.

The TNO research institute evaluated the risks on behalf of the economic affairs ministry to take into account the reduction in gas extraction. The quakes are caused by the ground settling after the gas has been removed.

The strongest earthquake so far to hit Groningen measured 3.6 on the Richter scale and took place in August 2012. The new maximum forecast is still 10 times as strong as this, the Financieele Dagblad points out.

The government is expected to decide on Friday if gas extraction should be further reduced.