Horizontal strain rate distribution on an active ice shelf rift from in-situ GPS data

Mass loss from the Antarctic ice sheet predominantly occurs at the fringing ice shelves via iceberg calving, which is controlled by the initiation and propagation of large rifts that precede iceberg detachment and can lead to ice shelf break-up. This paper reports on the analysis of Global Positioning System (GPS) data collected at an active rift system on the Amery Ice Shelf, East Antarctica, over two field seasons. Horizontal strain rates are determined for a network of 11 sites observed over three weeks during the 2004/05 Antarctic summer period, and the results are combined with, and compared to, strain rates obtained in the 2002/03 season. Maximum principal strain rates across the network vary between 6 and 32 [x 10-3/yr], while minimum principal strain rates are generally about 1-17 [x 10-3/yr]. Changes evident in the strain distribution can mostly be attributed to existing fractures passing through the GPS network and the episodic movement of the rift tip. It is confirmed that rift propagation in 2005/06 was slowing down. Opening rates are inferred from baselines situated normal to the rift. Analysis of the network using a cumulative sum approach is found to be an effective method to detect small baseline length changes associated with rift propagation.