Icequakes On Ekström Ice Shelf Near Atka Bay, Antarctica

Abstract

AbstractTwo seismic arrays recorded in an 11 month field experiment in 1985 the seismicity of Ekström Ice Shelf in the area of an ice rumple and an inlet, situated respectively about 10 km north-west and 7 km north of the German Antarctic station Georg von Neumayer (lat. 70°37′S., long. 08°22′W). Most of the focal depths of the icequakes considered until now are in the range 5–9 m; the ice-rumple area shows extremely high seismic activity. Tensile fracture is the most frequent fault mechanism, although there are a few shear-fracture events. The ice rumple’s seismicity provides information on the dynamics of the ice shelf in this area. A comparison of this time-dependent seismicity with tides suggests that most of this seismicity is induced by tides. The most active period of this seismicity starts at the beginning of low tide and ends at low tide. The location of the epicentres of icequakes recorded at that time and the digital recording on tapes of the seismicity without interruption for 396 h shows a jerky vertical movement of the ice shelf in response to tides; this can be interpreted as a kind of “grater effect”, especially at the southern ice-rock boundary of the ice rumple.The seismicity in the inlet is much less and tensile fracture seems to be the only fault mechanism.