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International database of Glacially Induced Faults (2020)

Munier, Raymond ; Adams, John ; Brandes, Christian ; [et al.]

PANGAEA

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Publication Date: 2024-04-20

Description: We provide a GIS data inventory of confirmed and proposed glacially-induced faults. Stresses, perturbated as a response to the advance and retreat of continental ice sheets and glaciers, can reactivate pre-existing faults. Previously referred to as "PostGlacial Faults" (PGFs), these faults are now called "Glacially-Induced Faults" (GIFs). More than a dozen kilometre-long and several metre-high fault-scarps have been identified in northern Fennoscandia since extensive investigations started in the 1960s and 1970s. Similar faults, but by far not of such dimensions, have also been described in eastern Canada. In other formerly glaciated areas in Europe, e.g., the southern parts of Sweden, Norway and Finland, the southern Baltic Sea, Denmark, northern Germany and Poland, and the Baltic countries, GIFs have rarely been observed and discussed in the literature. However, the number of studies with reliable field evidence for proposing such faults has increased considerably in recent years. The estimated fault movements are of minor magnitude, though, as compared with those in northern Fennoscandia. The database contains the confirmed GIFs in northern Fennoscandia including north-western Russia. The geological surveys in Norway, Sweden and Finland analysed recent LiDAR (Light Detection And Ranging) data from their countries, which helped uncover new faults and revise the geometry of the existing ones. In addition, we include several proposed GIFs outside this area, e.g., in southern Sweden, Denmark and Germany. Ongoing work suggests the occurrence of GIFs in Iceland, Canada and Antarctica. The database will be continually updated, considering new results. A summarized description of the GIF in this database is given in: Steffen, H., Olesen, O., and Sutinen, R. (2021). Glacially-Triggered Faulting. Cambridge University Press, Cambridge, UK, ca. 450 pp., expected publication February 2021.

Keywords: Glacially induced faults; Post-Glacial faults (PGF)

Type: Dataset

Format: application/zip, 161.1 kBytes

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The Iceland 1986 GPS geodetic survey: tectonic goals and data processing results (1993)

Foulger, G. R. ; Beutler, G. ; Bilham, Roger ; [et al.]

Springer

Journal of geodesy 67 (1993), S. 148-172

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ISSN: 1432-1394

Source: Springer Online Journal Archives 1860-2000

Topics: Architecture, Civil Engineering, Surveying

Notes: Summary The 1986 GPS survey of Iceland aimed to: (1) establish geodetic control in the South Iceland Seismic Zone (SISZ), to study destructive earthquakes there, (2) measure a country-wide network to form the basis of a new first order national network. 51 points were surveyed, with 20–30 km spacings within the SISZ and 100 km spacings elsewhere. The data were processed using the Bernese GPS software Version 3. Analysis was difficult due to poor satellite geometry and short-period ionospheric variations. However, an ambiguity-fixed, ionosphere-free solution gave accuracies of 1–2 cm in the horizontal and 2–3 cm in the vertical for the SISZ network and an ambiguity-free, ionosphere-free solution yielded accuracies of about 5 cm for the country-wide network. An ionosphere-free solution for the total survey with ambiguities fixed for the SISZ network only gave marginal additional improvements over the two separate solutions. GPS surveying has continued annually in Iceland with measurements in South Iceland in 1989 and 1992 (Hackman 1991; Sigmundsson 1992) and in North Iceland in 1987, 1990 and 1992 (Jahn et al. 1992; Foulger et al. 1992).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00806254

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Reinterpretation of the RRISP-77 Iceland shear-wave profiles (1996)

Menke, William ; Brandsdóttir, Bryndís ; Einarsson, Páll ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Geophysical journal international 126 (1996), S. 0

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ISSN: 1365-246X

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Two shear-wave profiles, E and G, collected during the 1977 Reykjanes Ridge Iceland Seismic Experiment have played an important role in models of the Icelandic crust. They were originally interpreted as indicating very low shear-wave velocities and abnormally low shear-wave quality factors in the 10–15 km depth range. These attributes, which are indicative of near-solidus temperatures, were used to support the hypothesis that the crust of Iceland is relatively thin (10–15 km) and underlain by partially molten material. More recent seismic data, however, contradict this hypothesis and suggest that the crust is thicker (20–30 km) and cooler. A re-examination of the RRISP-77 data indicates that the low shear-wave velocities are artefacts arising from source static anomalies (in the case of profile G) and misidentification of a secondary shear phase, SmS, as S (in the case of profile E). Furthermore, the attenuation occurs at ranges when rays from the shots pass near the Askja (profile E) and Katla and Oraefajokull (profile G) volcanoes. It may therefore have a localized source, and not be diagnostic of Icelandic crust as a whole. This new interpretation of the RRISP-77 shear-wave data is consistent with models having a thick, cold crust.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb05275.x

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Current rifting episode in north Iceland (1977)

Björnsson, Axel ; Saemundsson, Kristján ; Einarsson, Páll ; [et al.]

[s.l.] : Nature Publishing Group

Nature 266 (1977), S. 318-323

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] A major rifting episode is now occurring in north Iceland. This started on 20 December 1975, with a basaltic eruption, an exceptionally intense earthquake swarm and movement on an 80-km segment of the plate boundary. Inflation and deflation of the Krafla caldera indicate upwelling of magma and ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/266318a0

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Plate boundary deformation and continuing deflation of the Askja volcano, North Iceland, determined with GPS, 1987–1993 (1995)

Camitz, Johan ; Sigmundsson, Freysteinn ; Foulger, Gillian ; [et al.]

Springer

Bulletin of volcanology 57 (1995), S. 136-145

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ISSN: 1432-0819

Keywords: GPS ; Askja central volcano ; Caldera ; Deformation ; Plate boundary zone ; Magma chamber

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract GPS geodetic measurements were conducted around the Askja central volcano located at the divergent plate boundary in north Iceland in 1987, 1990, 1992 and 1993. The accuracy of the 1987 and 1990 measurements is in the range of 10 mm for horizontal components; the accuracy of the 1992 and 1993 measurements is about 4 mm in the horizontal plane. Regional deformation in the Askja region is dominated by extension. Points located outside a 30–45 km wide plate boundary deformation zone indicate a displacement of 2.4±0.5 cm/a in the direction N 99°E±12° of the Eurasian plate relative to the North American plate in the period 1987–1990. Within the plate boundary deformation zone extensional strain accumulates at a rate of ∼0.8 μstrain/a. Displacement of control points next to Askja (〉7 km from the caldera center) in the periods 1990–1993 and 1992–1993 show deflation and contraction towards the caldera. These results are in accordance with the results obtained by other geodetic methods in the area, which indicate that the deflation at Askja occurs in response to a pressure decrease at about 2.8 km depth, located close to the center of the main Askja caldera. A Mogi point source was fixed at this location and the GPS data used to solve for the source strength. A central subsidence of 11±2.5 cm in the period 1990–1993 is indicated, and 5.5±1.5 cm in the period 1992–1993. The maximum tensional strain rate, according to the point source model, occurs at a horizontal distance of 2.5–6 km from the source, at the same location as the main caldera boundary. Discrepancies between the observed displacements and predicted displacements from the Mogi model near the Askja caldera can be attributed to the regional eastwest extension that occurs at Askja.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00301404

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Seismicity around the Hekla and Torfajökull volcanoes, Iceland, during a volcanically quiet period, 1991–1995 (1997)

Soosalu, Heidi ; Einarsson, Páll

Springer

Bulletin of volcanology 59 (1997), S. 36-48

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ISSN: 1432-0819

Keywords: Key words Hekla ; Torfajökull ; Vatnafjöll ; South Iceland seismic zone ; Seismicity ; Low-frequency earthquakes ; Hekla eruption 1991

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract The volcano Hekla in south Iceland had its latest eruption in January–March 1991. The eruption was accompanied and followed by considerable seismic activity. This study examines the seismicity in the Hekla region (63°42′–64°18′N, 18°30′–20°12′W) during a period when the high activity related to the eruption had ceased, from July 1991 to October 1995. The aim is to define the level of the normal background seismicity of the area that can be compared to the eruption-related activity. The Hekla Volcano proper was generally aseismic during the study period. The most prominent earthquake cluster is in the neighbouring Torfajökull Volcano. The epicentres are concentrated in the western part of the caldera and west of it. The hypocentres are located at all depths from the surface down to 14 km, with highest activity at 5–12 km. Inside this cluster, in the northwest part of the caldera, is a spherical volume void of earthquakes, approximately 4 km in diameter and centred at 8 km depth. This is interpreted as a cooling magma body. Small, low-frequency events of volcanic origin were occasionally recorded at Torfajökull. This activity has mainly occurred in swarms and was most abundant during the first year of the study period, presumably reflecting some kind of connection to the 1991 Hekla eruption. Our study area also includes the easternmost section of the South Iceland seismic zone, a transform zone characterized by bookshelf faulting on transverse faults. Two lineaments of epicentres were identified, roughly corresponding to mapped faults of the South Iceland seismic zone. The hypocentres are relatively deep, mainly at 6–12 km, matching the general trend of hypocentral depth increasing toward the east. The seismicity is highest in the area of the mapped faults. However, the epicentres extend beyond them and indicate greater width of the South Iceland seismic zone, or 20–30 km rather than approximately 10 km as indicated by the length of the surface faults. The seismicity in the volcanic systems of Hekla and Vatnafjöll shows some characteristics of the South Iceland seismic zone. Epicentres are concentrated into two N–S lineaments, one of which coincides with the location of the 1987 Vatnafjöll earthquake (Mw=5.9), a strike-slip event on a N- to S-trending fault. The hypocentres of the Hekla–Vatnafjöll events are mainly at 8–13 km depth, which indicates a continuation of the depth trend of the earthquakes of the South Iceland seismic zone. The events located at Hekla proper and immediately north of it are all of low-frequency character, which can be held as an indication of volcanic origin. On the other hand, they show clear S arrivals at observing stations like normal high-frequency tectonic earthquakes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004450050173

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Plate boundary deformation and continuing deflation of the Askja volcano, North Iceland, determined with GPS, 1987–1993 (1995)

Camitz, Johan ; Sigmundsson, Freysteinn ; Foulger, Gillian ; [et al.]

Springer

Bulletin of volcanology 57 (1995), S. 136-145

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ISSN: 1432-0819

Keywords: Key words GPS ; Askja central volcano ; Caldera ; Deformation ; Plate boundary zone ; Magma chamber

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract GPS geodetic measurements were conducted around the Askja central volcano located at the divergent plate boundary in north Iceland in 1987, 1990, 1992 and 1993. The accuracy of the 1987 and 1990 measurements is in the range of 10 mm for horizontal components; the accuracy of the 1992 and 1993 measurements is about 4 mm in the horizontal plane. Regional deformation in the Askja region is dominated by extension. Points located outside a 30–45 km wide plate boundary deformation zone indicate a displacement of 2.4±0.5 cm/a in the direction N 99° E±12° of the Eurasian plate relative to the North American plate in the period 1987–1990. Within the plate boundary deformation zone extensional strain accumulates at a rate of ∼0.8 μstrain/a. Displacement of control points next to Askja (〈7 km from the caldera center) in the periods 1990–1993 and 1992–1993 show deflation and contraction towards the caldera. These results are in accordance with the results obtained by other geodetic methods in the area, which indicate that the deflation at Askja occurs in response to a pressure decrease at about 2.8 km depth, located close to the center of the main Askja caldera. A Mogi point source was fixed at this location and the GPS data used to solve for the source strength. A central subsidence of 11±2.5 cm in the period 1990–1993 is indicated, and 5.5±1.5 cm in the period 1992–1993. The maximum tensional strain rate, according to the point source model, occurs at a horizontal distance of 2.5–6 km from the source, at the same location as the main caldera boundary. Discrepancies between the observed displacements and predicted displacements from the Mogi model near the Askja caldera can be attributed to the regional east–west extension that occurs at Askja.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00301404

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The 1991 eruption of Hekla, Iceland (1992)

Gudmundsson, Agust ; Oskarsson, Niels ; Gronvold, Karl ; [et al.]

Springer

Bulletin of volcanology 54 (1992), S. 238-246

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ISSN: 1432-0819

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract The eruption that started in the Hekla volcano in South Iceland on 17 January 1991, and came to an end on 11 March, produced mainly andesitic lava. This lava covers 23 km2 and has an estimated volume of 0.15 km3. This is the third eruption in only 20 years, whereas the average repose period since 1104 is 55 years. Earthquakes, as well as a strain pulse recorded by borehole strainmeters, occurred less than half an hour before the start of the eruption. The initial plinian phase was very short-lived, producing a total of only 0.02 km3 of tephra. The eruption cloud attained 11.5 km in height in only 10 min, but it became detached from the volcano a few hours later. Several fissures were active during the first day of the eruption, including a part of the summit fissure. By the second day, however, the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed. The average effusion rate during the first two days of the eruption was about 800 m3 s−1. After this peak, the effusion rate declined rapidly to 10–20 m3 s−1, then more slowly to 1 m3 s−1, and remained at 1–12 m3 s−1 until the end of the eruption. Site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption. A notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption, but it levelled off on the 6th day and then remained essentially constant. The volume and initial silica content of the lava and tephra, the explosivity and effusion rate during the earliest stage of the eruption, as well as the magnitude attained by the associated earthquakes, support earlier suggestions that these parameters are positively related to the length of the preceeding repose period. The chemical difference between the eruptive material of Hekla itself and the lavas erupted in its vicinity can be explained in terms of a density-stratified magma reservoir located at the bottom of the crust. We propose that the shape of this reservoir, its location at the west margin of a propagating rift, and its association with a crustal weakness, all contribute to the high eruption frequency of Hekla.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00278391

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