During the night of 30-December-2021 at 04:16 UTC an earthquake with magnitude of Mw3,0 was felt in Selfoss town and Hveragerði town. This earthquake was part of a swarm in the area that is ongoing at the writing of this article.
There are no volcanoes in this area so this is only a tectonic activity. It is not possible to know when this earthquake swarm ends. This might be a aftershock activity after the Mw6,3 earthquake in SISZ that took place in this location in the year 2008. I expect this earthquake swarm to continue to few more days to weeks and then just end quietly.