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

Abstract

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.

DynaQlim – Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas

“…However, the rebound processes seem to play a certain role in triggering seismicity in intraplate areas of northern America (see James and Bent, 1994;Wu and Johnston, 2000;Grollimund and Zoback, 2001). The same is claimed for Greenland by Chung and Gao (1997) and by Chung (2002). The triggered earthquakes are concentrated either along zones of weakness or in regions of local stress concentrations.…”

New Frontiers in Integrated Solid Earth Sciences

“…In addition, predictions of the onset time and mode of failure are very sensitive to the proper selection of models for ice sheet and mantle rheology (Wu et al, 1999;Klemann and Wolf, 1999;Lund and Näslund, 2008). The same is claimed for Greenland by Chung and Gao (1997) and by Chung (2002). The same is claimed for Greenland by Chung and Gao (1997) and by Chung (2002).…”

Upper mantle dynamics and quaternary climate in cratonic areas (DynaQlim)—Understanding the glacial isostatic adjustment

“…Using a simple flexure argument, Chung and Gao (1997) and Chung (2002) proposed a similar connection for Greenland seismicity, and Antarctic earthquakes have been analyzed using viscoelastic mantle response modelling by Ivins et al (2003) and Kaufmann et al (2005). Recent studies also examine the possibility that during glacial transition times, when global sea-level rise rates are at their maximum (synchronous with Meltwater Pulses 1A and 1B) large interplate faults, such as the San Andreas in southern California, experience coeval enhancement of the shear loading rates that lead to large-scale rupture events (Lutrell and Sandwell, submitted for publication).…”