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Seismicity within a propagating ice shelf rift: The relationship between icequake locations and ice shelf structure
Ist Teil von
Journal of geophysical research. Earth surface, 2014-04, Vol.119 (4), p.731-744
Ort / Verlag
Washington: Blackwell Publishing Ltd
Erscheinungsjahr
2014
Link zum Volltext
Quelle
Wiley Online Library Journals
Beschreibungen/Notizen
Iceberg calving is a dominant mass loss mechanism for Antarctic ice shelves, second only to basal melting. An important process involved in calving is the initiation and propagation of through‐penetrating fractures called rifts; however, the mechanisms controlling rift propagation remain poorly understood. To investigate the mechanics of ice shelf rifting, we analyzed seismicity associated with a propagating rift tip on the Amery Ice Shelf, using data collected during the austral summers of 2004–2007. We apply a suite of passive seismological techniques including icequake locations, back projection, and moment tensor inversion. We confirm previous results that show ice shelf rifting is characterized by periods of relative quiescence punctuated by swarms of intense seismicity of 1 to 3 h. Even during periods of quiescence, we find significant deformation around the rift tip. Moment tensors, calculated for a subset of the largest icequakes (Mw > −2.0) located near the rift tip, show steeply dipping fault planes, horizontal or shallowly plunging stress orientations, and often have a significant volumetric component. They also reveal that much of the observed seismicity is limited to the upper 50 m of the ice shelf. This suggests a complex system of deformation that involves the propagating rift, the region behind the rift tip, and a system of rift‐transverse crevasses. Small‐scale variations in the mechanical structure of the ice shelf, especially rift‐transverse crevasses and accreted marine ice, play an important role in modulating the rate and location of seismicity associated with the propagating ice shelf rifts.
Key Points
Rift‐related seismicity controlled by mechanical heterogeneity
Back projection reveals that seismic deformation is continuous in region
Spacing of rift‐transverse crevasses controls the timing of seismic swarms