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IMO confirms continued inflation, seismic unrest at Mt. Þorbjörn, Iceland

reykjanes peninsula earthquakes october 25 - november 9 2023

The Icelandic Met Office (IMO) has issued an update on the seismic and volcanic activity at Mt. Þorbjörn on the Reykjanes Peninsula, providing new data on the ongoing seismic unrest that began in late October. The uplift at the GNSS station has seen additional enlargements since the 7 cm rise previously reported over a 10-day period, reflecting continued subterranean pressure changes. The IMO, alongside the Civil Protection Agency, remains on high alert for signs of magma ascent, which could indicate a new phase in the volcanic activity of the area.

Continuing its close monitoring of the Reykjanes Peninsula, the Icelandic Met Office (IMO) has provided a fresh update on the evolving geophysical phenomena at Mt. Þorbjörn on November 9. Following the considerable seismic swarm reported earlier, with over 18 500 earthquakes since October 25, the IMO’s latest data offers new insights into the region’s activity.

The recent patterns of seismicity and crustal deformation at Mt. Þorbjörn show a continuation of the intense geophysical unrest initially recorded.

In the 24-hour period leading up to 12:20 UTC on November 9, seismologists recorded approximately 1 400 earthquakes, with the most significant reaching a magnitude of 4.8 at 00:46 UTC. This event marks the largest seismic occurrence since the onset of heightened activity on October 25.

For context, seismic records from 24 hours to 14:40 UTC on October 8 indicated around 1 200 earthquakes. This activity has fluctuated, with 900 detected in the 24 hours preceding 13:30 UTC on November 7, and 1 300 in the same timespan leading up to 13:15 UTC on November 6. Earlier, there were 800 earthquakes registered in the 24 hours before 15:00 UTC on November 2, and 1 300 within the 24-hour timeframe ending at 11:30 UTC on October 30.

The uplift at the GNSS station on Mt. Þorbjörn, previously noted at 7 cm (2.7 inches) over 10 days, has shown a further increase. Since the last reported measurement, the land surface has continued to rise, though at a rate that is currently being analyzed for its implications on potential volcanic activity.

Models derived from data collected since October 27 highlighted a volume change nearly doubling that of the four prior inflation events between 2020 and 2022. The IMO’s update indicates that this trend of rapid crustal inflation continues, with further expansion of the sill-type intrusion at a depth of 5 km (3.1 miles). The magma or magmatic fluid inflow rate into this subsurface feature was previously estimated at about 7 m³/s, which was four times greater than rates observed during previous events.

interferogram reykjanes meninsula iceland october 28 - november 6 2023
Interferogram (InSAR) for the period of October 28 – November, 2023 shows that deformation in that period is around 7 cm (2.7 inches). SW of Mt. Þorbjörn is an offset in the deformation signal caused by fault movements by earthquakes. Credit: IMO, ICEYE
reykjanes peninsula earthquakes october 25 - november 9 2023 zoomed
Earthquakes detected from October 25 – November 9, 2023. Credit: IMO

Although there has been a noted shift in seismic activity—with a decrease north of Grindavík and a concentration in the Sundhnjúkagígar area northeast of Þorbjörn and west of Eldvörp—the likelihood of additional stress-induced seismic events persists. The frequency of earthquakes may have lessened since the peak of the swarm, but the potential for larger magnitude quakes and subsequent rockfalls, particularly near steep slopes, remains a concern.

The IMO, in concert with the Civil Protection Agency, continues to monitor and assess the situation. Their joint efforts aim to detect early signals of magma ascent, which would be characterized by increased shallow seismic activity, rapid surface deformation, and signs of volcanic tremor. While there has been no conclusive evidence of imminent surface magma movement to date, the authorities maintain a high level of readiness to respond to any swift changes in volcanic behavior.

Residents and visitors in the affected areas are advised to stay informed on the latest updates from the IMO and the Civil Protection Agency and to adhere strictly to any safety directives issued.

References:

1 Earthquake of M4.8 measured last night – IMO – November 9, 2023

2 Rapid crustal uplift at Mt. Þorbjörn, Iceland – The Watchers – November 6, 2023

Featured image credit: IMO

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