Seismotectonics of the central part of the South Iceland Seismic Zone

Bergerat, Françoise; Guðmundsson, Ágúst; Angelier, Jacques; Rögnvaldsson, Sigurður Th.

doi:10.1016/s0040-1951(98)00191-7

Cited by 48 publications

(24 citation statements)

References 14 publications

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“…10A, B); the less-developed trend is east-northeast. This conjugate set is similar to that found in the South Iceland Seismic Zone [49]. The set was active during the doming and intense earthquake swarm in Hengill 1994-2000 [2] and was also observed in the June 2000 earthquakes in South Iceland [50][51].…”

Section: Faults In the Hengill Volcanic Areasupporting

confidence: 76%

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Brittle tectonics of the Thingvellir and Hengill volcanic systems, Southwest Iceland: field studies and numerical modeling

Friese

2008

Geodinamica Acta

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This paper focuses on field studies and numerical models of fracture development in the area of the Hengill Central Volcano and its northern fissure swarm containing the Thingvellir Graben, in Southwest Iceland. Apart from additional field data on normal faults, a new detailed map of the Holocene fractures in the Thingvellir Graben is presented and used as a basis for numerical models on normal fault development. Field observations and models yield four basic results. First, hyaloclastite mountains in the area ("soft mechanical inclusions") tend to deflect or arrest propagating tension fractures and normal faults. Second, fractures with an en echelon arrangement and an overlapping configuration develop shear stress shadows and tend to prevent the linking up into larger fault segments. Third, fractures with an en echelon arrangement and underlapping configuration develop shear stress concentrations between nearby tips resulting in development of transverse shear faults (transfer fault). Fourth, colinear normal fault segments concentrate tensile stresses at their tips and encourage tip-to-tip growth into larger segments.

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Section: Faults In the Hengill Volcanic Areasupporting

confidence: 76%

“…The other main set of fractures is mostly NW-trending (to W-trending) (Fig. 9) and occur in some other parts of the volcanic zone such as in the EVZ, and in the South Iceland Seismic Zone [49].…”

Section: Faults In the Hengill Volcanic Areamentioning

confidence: 99%

Brittle tectonics of the Thingvellir and Hengill volcanic systems, Southwest Iceland: field studies and numerical modeling

Friese

2008

Geodinamica Acta

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“…In addition to the NNE and ENE faults, there are NW trending faults in the Holocene lava flows. The same strike-slip fault populations are observed in the Pleistocene rocks (GUDMUNDSSON, 1995a;PASSERINI et al, 1997;LUXEY et al, 1997;BERGERAT et al, 1998), namely NNE trending dextral faults, ENE trending sinistral faults as well as some NW trending faults (Fig. 7).…”

Section: Application To Icelandsupporting

confidence: 65%

“…For example, a fault zone may contain numerous faults at different scales that interact in various ways and often give rise to complex local stress fields (e.g., ZOBACK et al, 1987;ANGELIER et al, 1996;HOMBERG et al, 1997;BERGERAT et al, 1998;RÖ GNVALDSSON et al, 1998). This stress-field complexity makes general earthquake prediction, where the aim is accurate forecast of the time, place and size of the predicted earthquake, theoretically very difficult.…”

Section: Introductionmentioning

confidence: 99%

Evolution of Stress Fields and Faulting in Seismic Zones

Guðmundsson¹,

Homberg²

1999

Pure and Applied Geophysics

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Measurements indicate that stress magnitudes in the crust are normally limited by the frictional equilibrium on pre-existing, optimally oriented faults. Fault zones where these limitations are frequently reached are referred to as seismic zones. Fault zones in the crust concentrate stresses because their material properties are different from those of the host rock. Most fault zones are spatially relatively stable structures, however the associated seismicity in these zones is quite variable in space and time. Here we propose that this variability is attributable to stress-concentration zones that migrate and expand through the fault zone. We suggest that following a large earthquake and the associated stress relaxation, shear stresses of a magnitude sufficient to produce earthquakes occur only in those small parts of the seismic zone that, because of material properties and boundary conditions, encourage concentration of shear stress. During the earthquake cycle, the conditions for seismogenic fault slip migrate from these stress-concentration regions throughout the entire seismic zone. Thus, while the stress-concentration regions continue to produce small slips and small earthquakes throughout the seismic cycle, the conditions for slip and earthquakes are gradually reached in larger parts of, and eventually the whole, seismogenic layer of the seismic zone. Prior to the propagation of an earthquake fracture that gives rise to a large earthquake, the stress conditions in the zone along the whole potential rupture plane must be essentially similar. This follows because if they were not, then, on entering crustal parts where the state of stress was unfavourable to this type of faulting, the fault propagation would be arrested. The proposed necessary homogenisation of the stress field in a seismic zone as a precursor to large earthquakes implies that by monitoring the state of stress in a seismic zone, its large earthquakes may possibly be forecasted. We test the model on data from Iceland and demonstrate that it broadly explains the historical, as well as the current, patterns of seismogenic faulting in the South Iceland Seismic Zone.

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“…The structural features and the coastline are after EINARSSON andSAEMUNDSSON 1987. andANGELIER, 2000;BERGERAT et al, 1999;EINARSSON, 1991;RO¨GNVALDSSON and SLUNGA, 1994;STEFA´NSSON et al, 1993) the larger horizontal principal stress is NE-SW, i.e, it fits to an active N-S or E-W trending fault. This stress orientation seems to have been constant since Pliocene time (cf., BERGERAT et al, 1999). It indicates that the SISZ is not a weak fault zone like the San Andreas fault (cf., ZOBACK et al, 1987).…”

Section: The Tectonic Settingmentioning

confidence: 98%

Stress Changes Modelled for the Sequence of Strong Earthquakes in the South Iceland Seismic Zone Since 1706

Roth

2004

Pure and Applied Geophysics

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The South Iceland seismic zone is, roughly speaking, situated between two sections of the mid-Atlantic ridge, i.e., the Reykjanes Ridge southwest of Iceland and the Eastern Volcanic Zone on the island. It is a transform zone, where earthquakes are expected to occur on E-W-trending left-lateral shear faults, equivalent to conjugate, N-S-oriented right-lateral, rupture planes. In fact, earthquakes take place on en-e´chelon N-S-oriented faults, which is indicated by the distribution of main shock intensities, aftershocks as well as by surface fault traces. The stress field continuously generated in the fault zone by opening of the adjacent ridges is computed and superimposed on the stress field changes induced by a series of 13 earthquakes (M ‡ 6) between 1706 and 2000. The level of the pre-seismic stress field is analysed as well as the size of the area under high stress. Finally, the post-seismic stress field of June 2000 is analysed, to see where high stresses might have accumulated. The modelling indicates that the rupture planes located on separated parallel N-S-striking zones are dense enough to lead to an area-wide stress release by the series of events. The obtained pre-seismic stress level for most events is high and stable with the exception of situations when several strong shocks occur over a time span of several days, i.e., display typical main shock-aftershock patterns. The size of areas under high stress aside from of the rupture plane, i.e., where no event occurs at the specific time, is of medium to small size.

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Seismotectonics of the central part of the South Iceland Seismic Zone

Cited by 48 publications

References 14 publications

Brittle tectonics of the Thingvellir and Hengill volcanic systems, Southwest Iceland: field studies and numerical modeling

Brittle tectonics of the Thingvellir and Hengill volcanic systems, Southwest Iceland: field studies and numerical modeling

Evolution of Stress Fields and Faulting in Seismic Zones

Stress Changes Modelled for the Sequence of Strong Earthquakes in the South Iceland Seismic Zone Since 1706

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