The SIL data acquisition system—at present and beyond year 2000

Böðvarsson, Reynir; Rögnvaldsson, Sigurður Th.; Slunga, Ragnar; Kjartansson, Einar

doi:10.1016/s0031-9201(99)00032-1

Cited by 84 publications

(43 citation statements)

References 28 publications

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“…1). The SIL network is run by the Icelandic Meteorological Office (IMO; Bödvarsson et al 1999). The magnitude of completeness in the SISZ is around M L 0 (Wyss & Stefánsson 2006).…”

Section: Seismic Datamentioning

confidence: 99%

Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

et al. 2015

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two magnitude M W ∼ 6 earthquakes occurred on two adjacent N-S faults in the western South Iceland Seismic Zone. The first main shock was followed approximately 3 s later by the rupture on a parallel fault, about 5 km to the west. An intense aftershock sequence was mostly confined to the western fault and an E-W aligned zone, extending west of the main shock region into the Reykjanes oblique rift. In this study, a total of 325 well-constrained focal mechanisms were obtained using data from the permanent Icelandic SIL seismic network and a temporary network promptly installed in the source region following the main shocks, which allowed a high-resolution stress inversion in short time intervals during the aftershock period. More than 800 additional focal mechanisms for the time period 2001-2009, obtained from the permanent SIL network, were analysed to study stress changes associated with the main shocks. Results reveal a coseismic counter-clockwise rotation of the maximum horizontal stress of 11 ± 10 • (95 per cent confidence level) in the main rupture region. From previous fault models obtained by inversion of geodetic data, we estimate a stress drop of about half of the background shear stress on the western fault. With a stress drop of 8-10 MPa, the pre-event shear stress is estimated to 16-20 MPa. The apparent weakness of the western fault may be caused by fault properties, pore fluid pressure and the vicinity of the fault to the western rift zone, but may also be due to the dynamic stress increase on the western fault by the rupture on the eastern fault. Further, a coseismic change of the stress regime-from normal faulting to strike-slip faulting-was observed at the northern end of the western fault. This change could be caused by stress heterogeneities, but may also be due to a southward shift in the location of the aftershocks as compared to prior events.

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“…1). The SIL network is run by the Icelandic Meteorological Office (IMO; Bödvarsson et al 1999). The magnitude of completeness in the SISZ is around M L 0 (Wyss & Stefánsson 2006).…”

Section: Seismic Datamentioning

confidence: 99%

Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

et al. 2015

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“…To monitor seismic and volcanic activity in Iceland, IMO operates a nationwide digital network of 44 seismic stations (network name: SIL) [Bodvarsson et al, 1999] To monitor jokulhlaups, IMO has access to real-time data from water-level gauges and electrical conductivity meters operated by the National Energy Authority Hydrological Service (NEAHS) on rivers throughout the country Lightning in volcanic plumes is monitored by IMO's four-station lightning location system, in addition to real-time access to locations deter mined by the United Kingdom's Met Office.…”

Section: Monitoring Systemsmentioning

confidence: 99%

Forecasting and monitoring a subglacial eruption in Iceland

et al. 2005

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The recognition of geophysical precursors to volcanic activity is a primary challenge in volcano monitoring. That challenge was successfully met by scientists at the Icelandic Meteorological Office (IMO) before the 1 November 2004 eruption of Grímsvötn, a subglacial volcano beneath the Vatnajökull ice cap,Iceland (Figure 1). Seismic and geodetic precursors were properly recognized, leading to a timely eruption forecast and warning announcements. During the eruption, IMO's monitoring capability was greatly expanded by employing geophysical and meteorological observation tools, which enabled real‐time hazard assessment.

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“…Alsdorf and Smith (1999), Björnsson et al (2001a) and S. have used InSAR data to derive post-eruption ice-flow fields within the depressions formed by the eruptions, while Steinthorsson et al (2000) and Sigmarsson et al (2000) carried out petrologic and isotopic studies of the erupted tephra. Bödvarsson et al (1999) compiled a continuous seismic tremor diagram of the eruption.…”

Section: Introductionmentioning

confidence: 99%

The 1996 eruption at Gj�lp, Vatnaj�kull ice cap, Iceland: efficiency of heat transfer, ice deformation and subglacial water pressure

Guðmundsson

Sigmundsson

Björnsson

et al. 2004

Bulletin of Volcanology

133

121

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The 13-day-long Gjµlp eruption within the Vatnajökull ice cap in October 1996 provided important data on ice-volcano interaction in a thick temperate glacier. The eruption produced 0.8 km 3 of mainly volcanic glass with a basaltic icelandite composition (equivalent to 0.45 km 3 of magma). Ice thickness above the 6-km-long volcanic fissure was initially 550-750 m. The eruption was mainly subglacial forming a 150-500 m high ridge; only 2-4% of the volcanic material was erupted subaerially. Monitoring of the formation of ice cauldrons above the vents provided data on ice melting, heat flux and indirectly on eruption rate. The heat flux was 5-610 5 W m -2 in the first 4 days. This high heat flux can only be explained by fragmentation of magma into volcanic glass. The pattern of ice melting during and after the eruption indicates that the efficiency of instantaneous heat exchange between magma and ice at the eruption site was 50-60%. If this is characteristic for magma fragmentation in subglacial eruptions, volcanic material and meltwater will in most cases take up more space than the ice melted in the eruption. Water accumulation would therefore cause buildup of basal water pressure and lead to rapid release of the meltwater. Continuous drainage of meltwater is therefore the most likely scenario in subglacial eruptions under temperate glaciers. Deformation and fracturing of ice played a significant role in the eruption and modified the subglacial water pressure. It is found that water pressure at a vent under a subsiding cauldron is substantially less than it would be during static loading by the overlying ice, since the load is partly compensated for by shear forces in the rapidly deforming ice. In addition to intensive crevassing due to subsidence at Gjµlp, a long and straight crevasse formed over the southernmost part of the volcanic fissure on the first day of the eruption. It is suggested that the feeder dyke may have overshot the bedrock-ice interface, caused high deformation rates and fractured the ice up to the surface. The crevasse later modified the flow of meltwater, explaining surface flow of water past the highest part of the edifice. The dominance of magma fragmentation in the Gjµlp eruption suggests that initial ice thickness greater than 600-700 m is required if effusive eruption of pillow lava is to be the main style of activity, at least in similar eruptions of high initial magma discharge.

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The SIL data acquisition system—at present and beyond year 2000

Cited by 84 publications

References 28 publications

Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

Forecasting and monitoring a subglacial eruption in Iceland

The 1996 eruption at Gj�lp, Vatnaj�kull ice cap, Iceland: efficiency of heat transfer, ice deformation and subglacial water pressure

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The SIL data acquisition system—at present and beyond year 2000

Cited by 84 publications

References 28 publications

Temporal stress changes associated with the 2008 May 29MW 6 earthquake doublet in the western South Iceland Seismic Zone

Temporal stress changes associated with the 2008 May 29MW 6 earthquake doublet in the western South Iceland Seismic Zone

Forecasting and monitoring a subglacial eruption in Iceland

The 1996 eruption at Gj�lp, Vatnaj�kull ice cap, Iceland: efficiency of heat transfer, ice deformation and subglacial water pressure

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Product

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Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone

Temporal stress changes associated with the 2008 May 29M_W 6 earthquake doublet in the western South Iceland Seismic Zone