Download (6Mb) - NERC Open Research Archive

Long range shock waves from a large explosion underwater: experiment and dala
The gravity data emphasises this fact. The Tay Forth Bouguer Gravity
Anomaly Hap (Sheet 56°N 04°V) shows the Bell Rock gravity anomaly, a
10 mgal high, just to the southeast of the shot-line. The shot-line
itself is parallel to an elongated 5 mgal contour. North of Arbroath, and
north of the shot-line, the Bouguer values again rise to a 9 mgal high
anomaly (typical of lower Devonian sandstone complex). The Peterhead
Bouguer Gravity Anomaly Map (Sheet 57°N 02°V, 1:250000, Provisional
Edition) for the northeast of the shot-line still shows the trend of the
syncline parallel to the shot-line. All the geophysical evidence indicates
that the shot-line is following down the dip or core of the principal
syncline in the area and is parallel to the axis of major faulting.
The AMOCO VeIl, south of the shot-line, is just off to the south of the
Peterhead Sheet. It is likely that the structure in the well yields an
under-estimate of the thickness of the nearer surface sedimentary layers
on the shot-line, because the AMOCO VeIl is on the southern flanks of the
syncline of the shot-line. The Marr Bank Bouguer Gravity Anomaly Map
(Sheet 56°N 02°V, 1:250000, Provisional Edition) strengthens this
interpretation, showing that the AMOCO VeIl does lie on the southern flank
where the sedimentary layers are thinner, at about 10+mgal, within a
10 mgal contour high.
The Forth Tay Aeromagnetic Anomaly Map (1:250000) helps in the
interpretation of structure at the southwest end of the shot-line. This
map shows high positive anomalies west of Tentsmuir reaching upto +100 nT.
These anomalies extend about 13 km northeast, about 8 km offshore past
Tentsmuir. This implies that the Lower Devonian basalts are still
sufficiently near to the surface at this distance offshore to cause these
anomalies.
Veighing the structural evidence provided by the AMOCO Vell
(Table 6.2), the geological maps (Table 6.1), the aeromagnetic anomaly and
Bouguer gravity anomaly maps, leads to the geological cross-section in
Fig. 6.1 for the shallow upper crust. This geological cross-section can
be parameterised into two seismic models representative of the BGS sea-bed
site and the Tentsmuir hard rock coastal site (see Fig. 2.1), to
supplement the shot-point central model described above and in Table D2a.
36