Gravity survey from Anchor Bay to Għajn Tuffieħa

Abstract

In the gravity method of geophysical investigation variations in the earth's gravitational field are accurately measured and used to model the subsurface distribution of rock density and structure. The technique is widely used in mineral exploration and to a lesser degree in civil engineering to map the subsurface geology. This dissertation reviews the technique and describes a survey in the north of Malta. The survey was conducted along a 4.5 km long profile from Anchor Bay to Għajn Tuffieħa Ridge using a 111 Worden gravity meter. The purpose of this survey was to obtain the Bougeur anomaly and use it to model the subsurface geology. A total of 13 gravity stations were used to obtain accurate measurements of gravity corrected for instrument drift. The measurements were then reduced to datum by applying corrections for differences in latitude and elevation and for the effect of the Bougeur plate. The Bougeur anomaly was then extracted and interpreted using an iterative technique in which the distribution of density and structure of a model are widely changed until the theoretical anomaly fits the observed. The geology of the area is also discussed as a background for the gravity interpretation and the surface geology along the profile was used to constrain the models and provide boundary conditions. The model that fits best the measured anomaly is interpreted to define the subsurface structure that is largely controlled by a series of near-vertical normal faults extending to great depths.