Volcano-tectonic processes in the on-going Reykjanes peninsula volcanic episode as revealed by joint analysis and modeling of seismic and deformation data

Kristín S. Vogfjörd ¹, Michelle M. Parks¹, Vincent Drouin¹, Halldór Geirsson², Freysteinn Sigmundsson², Benedikt G. Ófeigsson¹

• Affiliations: ¹Icelandic Meteorological Office; ²Earth Science Institute, University of Iceland

• Presentation type: Talk [Invited]

• Presentation time: Friday 16:15 - 16:30, Room R280

• Programme No: 1.5.7

• Theme 1 > Session 5

---

Abstract

The N-America-Eurasia Plate Boundary (PB) along Reykjanes peninsula, Iceland, strikes ~N75-80E⁰, and intersects four ~NE-SW striking volcanic systems, including Reykjanes-Svartsengi and Fagradalsfjall. ~1.9 cm/year spreading towards ~N105E⁰ is oblique to the PB, requiring left-lateral slip along the boundary, but most slip occurs on N-S oriented, strike-slip faults. Since December 2019, release of tensional stress accumulated over 800 years has been triggered by magmatic intrusions into the upper crust beneath Fagradalsfjall and Svartsengi, causing 10 dike intrusions and volcanic eruptions, slip on the PB, and intense seismicity. Migration of high-precision relocated seismicity reveals location of magma up-flow near the PB beneath Fagradalsfjall, subsequent repeated inflow into vertical dikes propagating several kilometers NE and SSW and finally erupting.  Distribution of magma within the dikes is determined from inversion of InSAR and GNSS data. The intruding dikes have triggered slip on near-by faults releasing earthquakes up to M_W5.6, which in turn have triggered slip over large sections of the PB, as confirmed by seismicity and interferograms. Relocated seismicity patterns in 2020 and October 2023, suggest magma from below Fagradalsfjall may have flowed west and upwards, accumulating in a magma domain in the shallow crust adjacent to the PB at Svartsengi, until breaking out on November 10^th, forming the first dike intrusion at Sundhnúkur crate-row. Major tectonic rifting, generating ~30 M_W≥4 earthquakes accompanied the dike formation near Grindavík village, causing major surface fracturing and subsidence. Recharging of the domain has led to 7 more dike intrusions and eruptions along parts of the initial dike.