Inhomogeneous Tidal Strains in Queensbury Tunnel, Yorkshire

Abstract

Strain meters aligned along Queensbury Tunnel show amplitude variations of the diurnal tides of up to a factor of three, with smaller variations in phase. These observations are not easi!y explained because the semi-diurnal tides have different and smaller variations. The strain variations may be caused by local geological structures, but more observations and calculations are needed to test this hypothesis.

Topographic Effects on the Tidal Strain Tensor

“…The possibility -that measurement site inhomogeneities could affect the ratio of diurnal to semidiurnal strain tides was previously raised by King & Bilham (1973) in an analysis of their experimental data. According to the present theory, the dependence of this ratio upon the topography, in particular, may explain the anomalous results of Bilham, King & McKenzie (1974), who found a variation of the ratio of the semi-diurnal strain tide to diurnal strain tide along the length of the Queensbury Tunnel (UK) which is situated beneath a long hill. Since the slopes of the hill were not extremely large, they discounted the possibility of topographical influence on measured strains.…”

Some Calculations of Ocean Loading Strain Tides in Great Britain

“…This would seem to imply that areas such as Britain where there are large load strain tides cannot be used for upper mantle investigations, as the effects of structural variations may be masked by the uncertainties in the ocean load. But a full discussion of this point, and of the investigation of ocean tides through land-based strain measurements, necessitates a consideration of the local inhomogeneity problem (Bilham, King & McKenzie 1974) and will not be considered here. The distant ocean tides also have an effect on the load strain tide.…”

“…Only a few measurements of MZ and 0 1 load strain tides in Britain are available at present (Bilham et al 1972;Sinvhal 1973;Bilham et al 1974). A brief comparison of three of these measurements with the calculations is given in data are from Sinvhal 1973 andBilham et al 1974; all three sites are in Yorkshire.…”

“…A brief comparison of three of these measurements with the calculations is given in data are from Sinvhal 1973 andBilham et al 1974; all three sites are in Yorkshire. It should be emphasized that Clayton and Burdale are single instrument sites so that no estimate of local homogeneity is possible.…”

Local Effects on Strain Seismograms at Matsushiro Seismological Observatory - 2. Rayleigh Waves

“…However, as many geodesists have reported, local heterogeneity of media in the immediate vicinity of a site causes large variation in observed strain associated with Earth tides (for example, Bilham et al 1974). This fact implies that strain seismograms associated with the passage of seismic waves may also be affected by local heterogeneity.…”