Methods and Placement

Field sites are selected for good quality bedrock exposure, helicopter access and satellite sky-view. Dual-frequency 12-channel receivers with choke-ring antennas designed to exclude L1 multi-path are used. The receivers are kept in insulated boxes and powered from 60W solar panels and 80 amp-hours of gel-cell batteries. During the inital years stations were occupied for between 3 and 14 days, in recent years upto 90 days of data have been recorded per site per season.

The antennas are mounted on force-centered fixed-height mounts that are attached to threaded steel rods embedded into the bedrock. For more information on the equipment we use please see the equipment page.

Every site includes a small array to test for local motion to detect any locally occurring frost heave or rock fracture. In this way we ensure that our measurements are of regional motions and are not caused by local instability. Each micro-footprint consist of at least three markers arranged in a radial fashion between 20 and 250 meters away from the center point. These monuments are occupied during a “static survey” of between one and two hours. This survey is performed every couple of years.

Glacial Rebound

We are testing for glacio-isostatic rebound by arranging lines of monuments that stretch west-east from the interior of the region out to the coast of McMurdo Sound and beyond to the islands of the Ross Embayment. The rationale is that since the last glacial maximum the ice of the Ross Ice Shelf (part of the West Antarctic Ice Sheet) has thinned and started to float. The ice shelf is thought to have started to float in the region of McMurdo Station about 6,000 years ago. This unloading is shown by the numerous raised marine beaches in the area. The rebound signal caused by withdrawl of ice should be obvious when comparing the rebound rate on the inland flanks of the Transantarctic Mountains with those along the coastline and on the islands of the Ross Sea.

It is likely that there are north-south variations in the stability of the ice sheet based on the location of outlet glaciers and mountain barriers. We test for these varying load histories by examining rates of motion in lines along the inland flank of the mountains and up the coast of McMurdo sound. For monument locations see the site locations page and click on the site you are interested in.

Quaternary Fault Motion and Neotectonics

Antarctica has few seismic stations and is thought to be relatively inactive in geological terms, however there is evidence that the offshore Terror Rift is active and is splitting apart the Antarctic plate. The east-west lines we use to measure differential uplift across the mountains are also used to measure neo-tectonic activity across this rift.

We are surveying three special fault zones. These sites, at Beacon Valley, Hidden Valley and Mt Doorly are suspected to have been active during the Quarternary. Mt Doorly is extensively studied by Fitzgerald (1992) who conclude from appetite fission dating that the Transantarctic Mountains in that region have been sunject to 6km of uplift over the last 50Myrs. It is possible that the fault zone is still active. The two other sites have been selected as candidates for movement as there are fault features dissecting recent morianes there, indicating ongoing faulting. We are testing for movement by setting very large microfootprints into place, with baselines of some kilometers. Repeat measurements of these "macro-footprints" will measure any motion.

GIA Model Testing

Several models for the extent of the Antarctic Ice Sheets during the Last Glacial Maximum (LGM) have been proposed based on climatic and geological data. The popular models by James and Ivins (1998), Whar et al (1995)and Tushingham and Peltier (1991), show that there should be rebound of upto around 10mm a year for the region around McMurdo sound. TAMDEF is, in part an effort to verify these models and their input parameters whilst providing new constraints for future models.

GIANT/POLENET Project

The Geodetic Infrastructure of ANTarctica (GIANT) program is a SCAR initiative to provide a common geographic reference system for all Antarctic scientist and operators. The project will contribute to global geodesy for the study of the physical processes of the Earth and the maintenance of a precise terrestrial reference frame. In addition it will provide information for monitoring the horizontal and vertical motion of the Antarctic. As such TAMDEF provides a testbed for remote field technologies to be integrated into the future POLENETwork of remote polar geophysical observatories. TAMDEF stations also tie in measurements from tide guages and absolute gravity measurements to a common datum.