Technischer Bericht NTB 89-11

Between 1985 and 1989, the defections of the vertical were observed at 6 measurement stations at the Grimsel Test Site using Askania vertical pendulums.

The periodic range observed included the tides of the solid earth (T ~ 12 h and 24 h) and aperiodic tectonic movements (T ~ ∞). The analysis of tides gave differing amplitude factors and phase shifts at the measurement stations. This could be due to a large extent to lateral inhomogeneities between the stations in question. An investigation of the potential effects of reservoirs in the vicinity (T ~ weeks up to 1 year) showed that the effect of the Grimsel reservoir at the stations was extremely small. This could be explained by decoupling of movements along geological disturbed zones. The annual temperature wave, which is determined primarily by meteorological factors, is different at the various stations; this is also interpreted as the effect on the signal of inhomogeneities between the stations. The aperiodic movement, which has not yet been fully investigated, indicates subsidence in the vicinity of the reservoirs. A disturbed zone between the two reservoirs appears to have the effect of decoupling the movements with respect to one another, so that the stations to the north of this zone subside in the direction of the Räterichsboden reservoir (N/E direction), while the stations south of the zone tilt towards the south, i.e. in the direction of the Grimsel reservoir.