Gravity and seismic data in the Windless Bight area, Ross Island and the Dailey Islands to determine possible lithospheric deformation due to the loading by young Ross Island volcanics

Where loading of the lithosphere by young volcanic piles has occurred, the lithosphere is found to be displaced downward beneath the load and at distances of about 200-300 km from the centre of the load there are compensating upwards of lithosphere observed. From the amplitude and wavelength of both the solid surface and the free air gravity anomalies associated with loading, values of flexural rigidity and elastic thickness of the lithosphere may be determined. These two parameters, flexural rigidity and elastic thickness, are fundamental parameters of the earth that give a measure of the stiffness or flexural strength of the earth's lithospheric plates and are hence of importance to earthquake and related research. Isostatic compensation mechanisms were investigated over two seasons with seismic reflection, radio echo sounding and gravity observations carried out in the Windless Bight, Ross Island and Ross Ice Shelf area to examine possible lithospheric deformation due to the loading of the lithosphere by the young Ross Island volcanics. In the first season, 39 gravity stations were established in the Windless Bight area and in a joint effort with two USAP parties, 22 gravity measurements were made on Ross Island. Three seismic reflection stations were established and some time was spent experimenting with various shot and geophone arrangements. A week was spent in a joint seismic refraction project at the Dailey Islands. In the second season, a 600km round trip traverse southwest of Ross Island was completed with seismic reflection, radio echo sounding and gravity observations made at 10km intervals to determine the subsurface shape of the ice shelf, the ocean bottom, ocean bottom depth, ice thickness, the gravity anomaly field and deviations. A detailed grid of seismic, gravity and radio echo sounding observations were made in Windless Bight to outline a prominent moat feature suggested by the first seasons results. Two, 2km long multichannel seismic reflection lines were completed to provide a detailed picture of the sediment structure beneath the sea floor. A detailed gravity survey of the summit caldera area of Mt Erebus was also completed to obtain an accurate assessment of the total mass of Mt Erebus and an indication of where the centre of mass is located.