Australian seismic refraction results, isostasy and altitude anomalies

Abstract

Although there have been extensive seismic refraction measurements over areas of continental crust, the causes of variation in crustal thickness, and of variation in mean crustal seismic velocity, are poorly understood. If there is regional (3° × 3°) isostatic equilibrium of the crust, such as suggested by many studies of regional gravity, then crustal thickness variation should be caused largely by variation in surface altitude and crustal density. Seismic refraction results from Australia are used here to confirm that these crustal isostatic effects are a major (40%) cause of variation of crustal thickness even in a continent of little surface relief. However, there is an equally important regional variation in crustal thickness unrelated to crustal isostasy—this is thought to be due to density variation in the lower lithosphere1.