These might indicate that magma is making its way upwards. We saw this a few months ago, and it did not amount to anything in the end, but it is a little early to tell yet whether this pattern will be the same, or more serious.

Earthquakes in the Myrdalsjokull caldera July 7, 2014 (Icelandic Met Office)
For those who don’t know, Katla has often erupted after Eyjafjallajokull, which noticeably erupted back in 2010, shutting down air traffic at the time. And Katla is often the more violent of the two – hence the current interest.
I will update this if it develops into something that may turn out to be more serious.