______. ______ -L________ o. '0. '00. 200. "0. D~p l h {m 01 ice}. Fig. I. Variation of effective pressure with depth. Curves I and 3 were respectively calculated ...
Annals of Glaciology 12 1989 International Glaciological Society
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ICEQUAKES ON EKSTROM ICE SHELF NEAR ATKA BAY. ANTARCTICA
(Abstract) by H. von der Osten- Wold enburg (Institut fiir Allgemeine und Angewandte Geophysik , Ludwig-Maximilians- U ni ve rsitat Miinchen, Theresienstrasse 41 , D-8000 Miinchen 2, Federal Republic of . G erm any)
suggests that mos t of this seisml clty is induced by tid es. The most active period of thi s se ismicity starts at the beginning of low tide and ends at low tide. The locati on of the epicentres of icequakes reco rd ed at that tim e and th e digital recording on tapes of th e seismic it y with out interruption for 396 h shows a j erk y vertical movement of the ice shelf in response to tid es; thi s can be interpreted as a kind of "grater effect", es pec iall y at th e so uth ern ice--rock boundar y of the ice rumpl e. The seismicit y in th e inlet is much less and tensile fracture seems to be the onl y fault mec hani sm.
Two seismic arrays reco rd ed dur ing an II month f ield ex periment in 1985 the seismi city of E kstrom Ice Shelf in the area of an ice rumple and an inlet, situated respectively about 10 km north-wes t and 7 km north of the G erman Antarctic station Georg vo n Neum aye r (7 0 °37' S, 08 °22' W). Mos t of the focal depths of the icequ akes considered until now are in the range 5--9 m, and the ice- rumple area shows ex tremely high seismic ac ti vit y. Tensi le fr ac ture is the mos t f requ ent fault mechani sm, alth ough th ere are a few shear-frac ture events. The ice rumpl e's seismicity provides informati on on the dyn ami cs of the ice shelf in this area. A co mparison of thi s time - depend ent se ismicit y with tid es
RHEOLOGY OF POLAR GLACIER ICE
(Abstract) by P. Pim ie nta and P. Duval (La boratoire de Glacio logie et de G eo physique de l'Environnement, B.P. 96 , 38402 Saint-Martin-d'Heres Cedex, France) Theoretical considerati ons, labo ratory ex periments, and inclinometer data support a value ~2 for the exponent of the flow law relating stress and strain-rate in polar ice at low stresses (Pimienta and Duval, 1987). But a value of 3 was deduced from ice- shelf data by lezek and others ( 1985 ). The effect of longitudinal stresses, the development of preferred crystal orientatio ns, or experimental errors ex pla in th ese discrepanc ies. One way of identifyi ng deformation processes of ce ramics is to anal yze densification rates during isostatic pressure. In polar regions, ice particles sinter under the driving force of the pressure due to the weight of particles deposited on top of them. The final stage of press ure sintering corresponds to th e densificati o n of ice with closed At thi s stage, spherical pores, i.e. after close- off. den sification is determined by the creep of the thick spherical shell surrounding each bubble. Surface tensions are
