Earthquake swarms at Upptyppingar, north-east Iceland: A sign of magma intrusion?

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.

Lower-crustal earthquakes caused by magma movement beneath Askja volcano on the north Iceland rift

“…The Upptyppingar activity is beyond the scope of this paper, but these events are well documented with observations from the permanent Icelandic seismic network, and were also recorded on our network. This intense seismic activity in the Upptyppingar area, accompanied by crustal movements detected by GPS, has been interpreted as indicative of a magma intrusion (Jakobsdóttir et al 2008). a b c d e Fig.…”

The 2008 West Bohemia earthquake swarm in the light of the WEBNET network

“…Wyss et al, 1997;Dreger et al, 2000), the worldwide most intensive swarms occur apparently in Iceland, which is a part of the mid-Atlantic plate boundary (e.g. Stefansson et al, 2006, Jakobsdóttir et al, 2008. Intraplate earthquake swarms without active volcanism occur mainly in areas of enhanced crustal fluid activity, particularly in regions of Quaternary volcanism (Ibs-von Seht et al, 2008).…”

Volcano-tectonic interactions revealed by inversion of focal mechanisms: stress field insight around and beneath the Vatnajökull ice cap in Iceland

“…Also, both tectonic regimes occurred spatially in close proximity to each other, so no particular distribution was observed. This feature was also highlighted in the Upptyppingar swarm (Jakobsdóttir et al, 2008;White et al, 2011). However, then the location of the maximum amount of rotation seemed to be located northern of the Barðarbunga volcano where the main shock occurred, and in an ice-free domain ( Figure 13B).…”

“…Such flip of focal mechanisms over a short time period was seen in the Upptyppingar swarm in 2007 in Iceland, northeast of the glacier (Jakobsdóttir et al, 2008;White et al, 2011). Substantial changes in rotation of focal solutions were mainly observed immediately prior to the eruption (approximately 15 h before its onset) and during the first days of the eruption from 30th of September to 2nd of October).…”

“…For instance, a large swarm of earthquakes occurred in 2007 north of the Vatnajökull in the Upptyppingar region at a depth of 14-17 km and it is believed that this was due to dyke intrusion (Jakobsdóttir et al, 2008). Analyses of P, B, and T-axes from fault plane solutions achieved by the Icelandic national survey showed two preferred directions of the T-axis: one is in agreement with the direction of regional spreading and another one lies perpendicular to this (Jakobsdóttir et al, 2008;Plateaux et al, 2012). Interestingly, such an observation has been described for other volcano-tectonic regions such as Mount Etna (Cocina et al, 1996;Patané and Privitera, 2001), Guagua Table 1).…”