icefest,
Due to distractions, the following is all that I can provide in support of your theory of the current major calving risk (crack pattern) for the PIIS.
First, the first attached image shows the cracking pattern in a concrete deep beam. If you consider only the right half of this beam, the stress patterns have some degree of relevance to the stress/cracking patterns of the PIIS associated with its risk of a potential major calving in the near future.
Second, regarding the SW Tributary Glacier (that feeds into the PIIS), the linked reference (with a free pdf and see the second attached reference figure) presents a very interesting discussion:
http://www.igsoc.org/journal/59/217/j13J050.pdfWeak bed control of the eastern shear margin of Thwaites Glacier, West Antarctica; Joseph A. MacGREGOR, Ginny A. CATANIA, Howard CONWAY, Dustin M. SCHROEDER, Ian JOUGHIN, Duncan A. YOUNG, Scott D. KEMPF, & Donald D. BLANKENSHIP; Journal of Glaciology, Vol. 59, No. 217, 2013 doi: 10.3189/2013JoG13J050
Third, the two following references (including Bassis as a co-author) are related to cracking in ice shelves:
Heeszel, D. S., H. A. Fricker, J. N. Bassis, S. O'Neel, and F. Walter (2014), Seismicity within a propagating ice shelf rift: The relationship between icequake locations and ice shelf structure, J. Geophys. Res. Earth Surf., 119, 731–744, doi:10.1002/2013JF002849.
http://onlinelibrary.wiley.com/doi/10.1002/2013JF002849/abstractAbstract: "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."
C. C. Walker, J. N. Bassis, H. A. Fricker, and R. J. Czerwinski, (2013), "Structural and environmental controls on Antarctic ice shelf rift propagation inferred from satellite monitoring", Journal of Geophysical Research: Earth Surface, Volume 118, Issue 4, pages 2354–2364, DOI: 10.1002/2013JF002742.
http://onlinelibrary.wiley.com/doi/10.1002/2013JF002742/abstractAbstract: "Iceberg calving from ice shelves accounts for nearly half of the mass loss from the Antarctic Ice Sheet, yet our understanding of this process is limited. The precursor to iceberg calving is large through-cutting fractures, called “rifts,” that can propagate for decades after they have initiated until they become iceberg detachment boundaries. To improve our knowledge of rift propagation, we monitored the lengths of 78 rifts in 13 Antarctic ice shelves using satellite imagery from the Moderate Resolution Imaging Spectroradiometer and Multiangle Imaging Spectroradiometer between 2002 and 2012. This data set allowed us to monitor trends in rift propagation over the past decade and test if variation in trends is controlled by variable environmental forcings. We found that 43 of the 78 rifts were dormant, i.e., propagated less than 500 m over the observational interval. We found only seven rifts propagated continuously throughout the decade. An additional eight rifts propagated for at least 2 years prior to arresting and remaining dormant for the rest of the decade, and 13 rifts exhibited isolated sudden bursts of propagation after 2 or more years of dormancy. Twelve of the fifteen active rifts were initiated at the ice shelf fronts, suggesting that front-initiated rifts are more active than across-flow rifts. Although we did not find a link between the observed variability in rift propagation rate and changes in atmospheric temperature or sea ice concentration correlated with, we did find a statistically significant correlation between the arrival of tsunamis and propagation of front-initiated rifts in eight ice shelves. This suggests a connection between ice shelf rift propagation and mechanical ocean interaction that needs to be better understood."
Fourth (and finally), the following summary research statement provide an idea of the ice shelf fracturing and flow pattern of the Filchner Ronne Ice Shelf from 2003 to 2004 field data, which has some moderate relevance to the PIIS situation:
Hulbe, C. L., and C. M LeDoux. 2011. MOA-derived Structural Feature Map of the Ronne Ice Shelf. [indicate subset used]. Boulder, Colorado USA: National Snow and Ice Data Center.
http://dx.doi.org/10.7265/N5PR7SXR. Summary statement:
"This data set provides a structural feature map of the Ronne Ice Shelf in Antarctica (also known as the Filchner-Ronne Ice Shelf). The map was developed as part of a project to study fracture propagation in the Ronne Ice Shelf, with special focus on the Evans Ice Stream. Features were digitized from the MODIS Mosaic of Antartica (MOA), a composite of individual Moderate Resolution Imaging Spectradiometer (MODIS) images taken between 20 November 2003 and 29 February 2004, with an effective resolution of 125 m. The data set includes estimates of the shelf boundary, including ice stream grounding zones, outlets of glaciers feeding the shelf, extents of islands and ice rises, and the location of the shelf front, and features observed within the shelf, including suture zones between ice streams, streaklines, fractures (crevasses and rifts), and fold-like features. Individual features can be extracted as a group of points and grouping is used to facilitate identification and plotting."
Best,
ASLR