Exceptionally intense earthquake swarm near Þorbjörn, Iceland

reykjanes peninsula earthquakes october 28 2023

An exceptionally intense earthquake swarm lasting nearly two hours started at Þorbjörn in Iceland at 08:40 on October 31, 2023. The largest event registered an M3.7, and the activity signaled potential magma movement at depths between 1.5 km and 5 km (0.93 – 3.1 miles).

The Icelandic Met Office (IMO) reported a substantial earthquake swarm at Þorbjörn, lasting almost two hours and starting at 08:40 local time. The strongest earthquake in this series was measured at M3.7. These events took place at depths ranging between 1.5 km and 5 km (0.93 miles and 3.1 miles), primarily east of the uplift center that had been observed in recent days.

GPS measurements provided additional data that supported the possibility of magma movements beneath the surface. However, the rate of uplift, which had accelerated about four days prior, showed signs of deceleration.

LOS deformation between October 26 - 28 2023
“Line-of-sight” (LOS) deformation measured by the ICEYE SAR satellite between 05:21 UTC on October 26 and 05:21 UTC on October 28, 2023. Satellite data provided in collaboration with ICEYE

Earlier on the same day, Civil Defense authorities and stakeholders held a meeting to discuss the latest data and develop possible response strategies for the Reykjanes Peninsula, where Þorbjörn is located. While the situation is currently stable, the potential for rapid changes has not been ruled out.

IMO continues to closely monitor any shifts in seismic activity, particularly if it moves closer to the Earth’s surface. Such a shift could indicate that magma is breaking through the crust. At this point, the earthquakes have not shown signs of becoming shallower.

The broader geological context also adds another layer to the situation. Increased earthquake activity in the nearby Svartsengi area, potentially resulting from long-term rifting, could have created weaknesses in the Earth’s crust. These weaknesses may facilitate the magma’s upward movement, although it’s worth noting that similar magma movements in the past have not necessarily led to a volcanic eruption.

References:

1 Series of earthquakes northwest of Þorbjörn this morning is a sign of magma flow – IMO – October 31, 2023

Featured image credit: IMO

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