Geology Reference
In-Depth Information
When geophysics works well, the results can be extremely useful and
the method cost-effective. The main options and constraints are set out
in BS 5930: 1999 and Clayton (1995).
Seismic refraction techniques, using an energy source ranging from a
sledgehammer to explosives, can be useful on land and in shallow
water for
finding depth to bedrock, for example, to identify buried
channels that could otherwise only be proved by numerous boreholes
or probes. Large areas can be investigated quite cheaply and quickly.
The method works best where there is a strong contrast in seismic
discontinuity dipping 54
degrees in a 240 direction
Oblique view
across hemisphere
with intersecting
planar feature
(a)
N
E
W
direction of
dip (240)
S
reference sphere
(lower hemisphere)
trace of intersection
where plane
cuts hemisphere
Side view along
strike of plane
projection of
trace into
horizontal plane
dipping plane
projection of pole
into horizontal plane
(b)
direction of dip
pole normal to plane
trace of plane
Horizontal plan
view
N
angle of dip
measured on
reference net
(c)
⋅
pole to plane
90
measured on
reference net
°
direction of dip
projection of complete
trace as a 'great circle'
Sliding direction
for a wedge
formed by two
planes
N
(d)
pole to great
circle 1
pole to great
circle 2
⋅
Angle of
inclination for
line of
intersection
between planes
⋅
28
°
great circle
for plane 1
50/238
great circle for
plane 2
30/290
