I have seen a lot of people worrying about earthquakes and earthquake swarms that take place in Iceland on regular basic. Those worries are not needed as Iceland gets about one to two earthquake swarms on average over the course of one week. Most of the earthquakes that take place in Iceland are tectonic in nature. There are also volcano related earthquakes. But they can be spotted by there location in connection with the volcano in question (Katla, Grímsfjall, etc..).
The reasons for the earthquake swarms in Iceland is geological and is because Iceland sits on a rift zone. This can be shown clearly on this picture here.
Click on picture to get better resolution.
This map clearly shows all the zones in Iceland. In this areas most of Iceland earthquakes happens. But also a big part of Iceland earthquakes happen in areas like SISZ and TFZ.
On the normal week there are about 150 to 400 earthquakes in Iceland over the week. Most of them are in the size ML0.0 and up to ML2.8. Most week have one or two earthquakes that are ML3.0 to ML3.8 in size. On a quiet week there are about 50 to 100 earthquakes, most of them less then ML2.5 in size. When there is a busty week in Iceland the earthquakes numbers can easily go over 2000 and sometimes well over 5000 earthquakes. When that happens IMO doesn’t even bother in classifying and locating all the earthquakes that take place. But they are saved anyway in IMO database.
Picture taken from this blog: Earthquake in Iceland (2008); This blog has more images about the tectonic process in Iceland.