Update : The aftershock sequence has started. Max aftershock so far was M5.1. The aftershock sequence means at least that the source of the earthquake was tectonic and not a volcano explosion (there is always an error margin in the calculation of earthquake epicenters).
Ambrym volcano has erupted 50 times in the last 150 years, an average of once every 3 years with eruptions usually between VEI 1 and VEI 3. In 1950, a VEI 4 eruption occurred (equivalent to that of the Icelandic eruption of 2010).
Around 2000 years ago, it erupted with VEI 6 (equivalent to Pinatubo 1991).

Update 13:45 UTC : Ambrym Island is also the location of the very active Ambrym volcano (Marum and Benbow craters). We do not know as yet whether the earthquake has influenced the activity of the lava lake in the Marum crater.