The Seismicity of Greenland

Gregersen, Søren

doi:10.1007/978-94-009-2311-9_20

Cited by 12 publications

(6 citation statements)

References 9 publications

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“…Therefore, this difference in strike direction may reflect regional variations in fault systems and/or stress variability. The strike directions of both Ungava earthquakes (1989;Bent 1994) are similar to the direction of the 2007, 2008c and 2009 earthquakes (Fig. 7).…”

Section: Focal Mechanismmentioning

confidence: 52%

“…Basham et al 1977; Quinlan 1984; Adams 1989a; Adams et al 1991; Henderson 1991; Arvidsson & Kulhanek 1994; Bent 1994; Adams 1996; Johnston 1996; Uski et al 2003; Steffen & Wu 2011), and around the current ice margin of the Greenland and Antarctic ice sheets (e.g. Okal 1980; Adams & Akoto 1986; Gregersen 1989; Chung & Gao 1997; Tsuboi et al 2000; Chung 2002; Gregersen 2006; Reading 2007; Voss et al 2007). As several parts of the Earth remain covered by ice sheets, the relationship between deglaciation and seismicity is important for the understanding of the trigger mechanism of intraplate earthquakes, the mitigation of seismic risk for infrastructure planning and design, and the understanding of climate change and Heinrich events (Hunt & Malin 1998), which were possibly triggered by ice‐load‐induced earthquakes.…”

Section: Introductionmentioning

confidence: 99%

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Moment tensors, state of stress and their relation to post-glacial rebound in northeastern Canada

Steffen

Eaton

2012

Geophysical Journal International

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SUMMARY In the stable craton of northeastern Canada moderate seismicity as well as glacial isostatic adjustment (GIA) has been observed. We investigate five earthquakes with moment magnitudes between 3.6 and 4.1 that have occurred in northern Hudson Bay since 2007, which may be triggered by GIA. Focal mechanisms of the earthquakes are determined using a waveform‐fitting procedure for surface waves, in which the best double‐couple mechanism is obtained through a grid search over strike, dip, and rake. All events exhibit a thrust‐fault mechanism, in general agreement with mechanisms of previously analysed earthquakes in that area. Stress‐inversion results incorporating our new mechanisms as well as previously published results exhibit significant differences from previously calculated stresses from GIA models. For the first time, maximum horizontal stress direction SHmax is compared to the modelled stress values for northeastern Canada. We find that the maximum horizontal stress direction strikes roughly NNW–SSE, in contrast to previously inferred NE‐SW orientation of SHmax. Our results indicate that the local stress field in northern Hudson Bay deviates from regional stresses resulting from the existence of a roughly E–W oriented zone of faulting, which is not included in existing GIA models.

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Section: Focal Mechanismmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Moment tensors, state of stress and their relation to post-glacial rebound in northeastern Canada

Steffen

Eaton

2012

Geophysical Journal International

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“…A recent report by Fig. On the other hand Gregersen (1989Gregersen ( , 2006 has argued, based on interpretations of the same data, that the main stress field nowadays is related to lithospheric motion. Earthquake map of Greenland for the years from January 1970 to June 2004.…”

Section: Supplementary Stress Information From Greenlandmentioning

confidence: 91%

Stress change over short geological time: the case of Scandinavia over 9000 years since the Ice Age

Gregersen

Voß

2009

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Palaeoseismological investigations are used in many regions of the world to extend back in time the earthquake statistics of historical written or oral records as well as instrumental information. This is very valuable for discussions of earthquake hazard, but it only applies to areas of stable stress regime. Although the intraplate areas of Scandinavia and Greenland have experienced only rather small earthquakes within the human timescale, they serve as a clear warning on the application of palaeoseismology for hazard studies in regions where the stresses have changed.In a small part of Scandinavia, where recent earthquake activity is not significantly different from that of its surroundings, large faults have been discovered and several have been investigated via palaeoseismology. They are interpreted to show the occurrence of large earthquakes about 9000 years ago. Signs of this are coincident landslides as well as liquefaction in loose sediments, which are well dated through varve-counting.In contrast to this the present-day stress release in earthquakes and in surface rock deformations is mainly caused by plate motion. Regional investigations in Scandinavia and Greenland/North America, as well as those included in the World Stress Map Project of the 1990s, have shown compression within the plate, mainly in the direction of absolute plate motion. The ice cap influence has disappeared. So stress reorganization is clearly indicated over the short geological timespan of 9000 years. Into this argument goes the observation from Greenland and Antarctica, that no earthquakes occur under the ice caps. For Scandinavia the argument is that no earthquakes occurred under the ice sheet during the Ice Age, and that the stored stresses were released when the ice sheet melted 9000 years ago. This does emphasize a warning. There are regions of the globe where palaeoseismological investigations can give a fantastic extension of the short-term historical earthquake records. But in some regions stress reorganization has changed this condition.

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“…The tectonic implications of this event were discussed in CHUNG and GAO (1997) and are not repeated here. The seismic movement associated with this quake may fit into the plate-motion interpretation suggested by GREGERSEN (1989).…”

Section: Evidence Of Postglacial Fault Reactivationmentioning

confidence: 99%

“…The earthquakes of October 14, 1998, August 10, 1993(this paper), and July 11, 1987(CHUNG and GAO, 1997 are shown as stars. Seismicity in Greenland 1940-1985 based on instrumental data is from GREGERSEN (1989). Focal mechanisms of major events are presented with a lower hemisphere equal-area projection.…”

Section: Introductionmentioning

confidence: 99%

Earthquakes Along the Passive Margin of Greenland: Evidence for Postglacial Rebound Control

Chung¹

2002

Pure and Applied Geophysics

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An intriguing observation in Greenland is a clear spatial correlation between seismicity and deglaciated areas along passive continental margins, a piece of evidence for earthquake triggering due to postglacial rebound. Another piece of evidence for induced seismicity due to deglaciation derives from earthquake source mechanisms. Sparse, low magnitude seismicity has made it difficult to determine focal mechanisms from Greenland earthquakes. On the basis of two normal faulting events along deglaciated margins and from the spatial distribution of epicenters, earlier investigators suggested that the earthquakes of Greenland are due to postglacial rebound. This interpretation is tested here by using more recent data. Broadband waveforms of teleseismic P waves from the August 10, 1993 (m b ¼ 5.4) and October 14, 1998 (m b ¼ 5.1) earthquakes have been inverted for moment tensors and source parameters. Both mechanisms indicate normal faulting with small strike-slip components: the 1993 event, strike ¼ 348.9°, dip ¼ 41.0°, rake ¼ )56.3°, focal depth ¼ 11 km, seismic moment ¼ 1.03 · 10 24 dyne-cm, and M w ¼ 5.3; the 1998 event, strike ¼ 61.6°, dip ¼ 58.0°, rake ¼ )95.5°, focal depth ¼ 5 km, seismic moment ¼ 5.72 · 10 23 dynecm, and M w ¼ 5.1. These and the two prior events support the theory that the shallow part of the lithosphere beneath the deglaciated margins is under horizontal extension. The observed stress field can be explained as flexural stresses due to removal of ice loads and surface loads by glacial erosion. These local extensional stresses are further enhanced by the spreading stress of continental crust and reactivate preexisting faults. Earthquake characteristics observed from Greenland suggest that the dominant seismogenic stresses are from postglacial rebound and spreading of the continental lithosphere.

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The Seismicity of Greenland

Cited by 12 publications

References 9 publications

Moment tensors, state of stress and their relation to post-glacial rebound in northeastern Canada

Moment tensors, state of stress and their relation to post-glacial rebound in northeastern Canada

Stress change over short geological time: the case of Scandinavia over 9000 years since the Ice Age

Earthquakes Along the Passive Margin of Greenland: Evidence for Postglacial Rebound Control

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