A microgravimetric network for secular gravity studies in Scotland

Abstract

Tests with the LaCoste and Romberg gravity meter G-275 show that random reading errors generate a standard deviation of less than 0.02 gu (2 µgal) under typical microseismic conditions. Reproducible, systematic errors are commonly an order of magnitude larger, due mainly to residual tidal effects and drift induced by clamping. The latter, possibly related to thermal gradients in the oven, can be eliminated by observing a long-enough section of the drift curve at each field station so that equilibrium is reached there. A measurement of the gravity difference between the NGRN (73) sites at Edinburgh and Linlithgow, giving 5.5655± 0.018 (se) gu, is described as an example of the method. A loop of eight gravity stations associated with Ordnance Survey Fundamental Bench Marks, east—west between Dunbar and Bowling (Dumbartons) and northwards to Crubenmore (Inverness) is being measured as the basis of a secular gravity study by a calibrated small-difference method. The uses of such a network are discussed.