Intense seismic activity in Þorbjörn, Iceland: possible magma movement
On October 31, 2023, an extraordinary seismic swarm lasting almost two hours occurred in Þorbjörn, Iceland, starting at 08:40. The most significant event recorded a magnitude of 3.7 and the activity signaled possible movement of magma at depths between 1.5 km and 5 km.
Details of the seismic swarm
Report from the Icelandic Meteorological Office
The Icelandic Meteorological Office (IMO) reported a notable earthquake swarm in Þorbjörn, which lasted almost two hours and began at 08:40 local time. The strongest earthquake in this series was measured at magnitude 3.7. These events occurred at depths between 1.5 km and 5 km, mainly east of the uplift center that had been observed in the previous days.
GPS measurements and magma movements.
The GPS measurements provided additional data supporting “the possibility” of magma movements beneath the surface. However, the pace of increase, which had accelerated about four days earlier, “showed signs of” slowing.
Implications and responses
Response and follow-up strategies
On the same day, Civil Protection authorities and stakeholders held a meeting to discuss the latest data and develop possible response strategies for the Reykjanes Peninsula, where Þorbjörn is located. Although the current situation is stable, the possibility of rapid changes cannot be ruled out.
The IMO continues to closely monitor any changes in seismic activity, particularly as it approaches the Earth’s surface. Such a change could indicate that magma is breaking down the crust. So far, the earthquakes have shown no signs of abating.
Broader geological context
The broader geological context adds another layer to the situation. An increase in seismic activity in the nearby Svartsengi area, potentially resulting from long-term rifting, may have created weaknesses in the Earth’s crust. These weaknesses can facilitate the upward movement of magma, although it is worth noting that similar movements of magma in the past have not necessarily led to a volcanic eruption.