Abstract
In 2007, intense swarms of deep, tectonic earthquakes, amounting to at least 5 300 epicentres, were detected near to Mount Upptyppingar, which forms part of the Kverkfjöll volcano system in Iceland's Northern Volcanic Zone. Although micro-seismicity is common within such volcanic regions, the Upptyppingar swarms have been more intensive and persistent than any other deep-seated seismicity observed in Iceland. Here we outline the spatial and temporal changes in ongoing seismicity that began in February 2007; in addition, we document enhanced levels of GPS-derived crustal deformation, recorded within 25 km of the area of swarming. Besides displaying spatial clustering, the Upptyppingar micro-earthquakes are noteworthy because: (i) they concentrate at focal depths of 14-22 km; (ii) the swarms comprise brittle-type earthquakes < 2 in magnitude, yielding a b-value of 2.1; and (iii) several of the swarms originate at focal depths exceeding 18 km. Additionally, different parts of the affected region have exhibited seismicity at different times, with swarm sites alternating between distinct areas. The activity moved with time towards east-north-east and to shallower depths. Linear regression approximates the seismicity on a southward-dipping, ∼41° plane. Alongside sustained earthquake activity, significant horizontal displacement was registered at two permanent GPS stations in the region. High strain rates are required to explain brittle fracturing under visco-elastic conditions within the Earth's crust; similarly, intense, localised deformation at considerable depth is necessary to reconcile the measured surface deformation. Such remarkable seismicity and localised deformation suggests that magma is ascending into the base of the crust.
Original language | English |
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Pages (from-to) | 513-528 |
Number of pages | 16 |
Journal | Studia Geophysica et Geodaetica |
Volume | 52 |
Issue number | 4 |
DOIs | |
Publication status | Published - 2008 |
Bibliographical note
Funding Information:Acknowledgements: This research was funded partly by the European Union project VOLUME (018471). It is based on the work of the monitoring team at the Physics Department of the Icelandic Meteorological Office. The figures were made with GMT (Wessel and Smith, 1998) and R (R Development Core Team, 2008). We thank L. Eisner and two anonymous reviewers for insightful comments on this article.
Other keywords
- Crustal deformation
- Ductile crust
- Earthquake swarm
- Iceland
- Magma intrusion