Figure 1 shows a simplified model of a continental margin called
‘Birkbeck Margin’. The densities of water, lithosphere and
asthenosphere are 1.03 g/cm3, 2.67 g/cm3 and 3.10 g/cm3
respectively. !
Figure 1 Simplified model of Birkbeck Margin !! f) Explain why the free-air anomaly of the Birkbeck Margin can be
calculated by adding the measured gravity anomalies of the two
half-slabs in d). Why is it not necessary to know the latitude of the
Birkbeck Margin in the calculation? !!g) By using information given in f), calculate the free-air anomaly
across Birkbeck Margin and sketch it in a graph.
!
!h
) Explain how the expected Bouguer anomaly of Birkbeck Margin
(Figure 1) will be different from the free-air anomaly. It is not
necessary to calculate or sketch the Bouguer anomaly in a
graph. !!!!i) By considering the pressure difference at 100 km below the sea
level of Birkbeck Margin (Figure 1), comment on the isostatic
equilibrium of the Birkbeck Margin. Assume that g = 9.8 m/s2 at
all depths. !!!!j)* By considering Equation 1, explain how the free-air anomaly
profile (part g) can be used to determine the isostatic status of
Birkbeck Margin.
‘Birkbeck Margin’. The densities of water, lithosphere and
asthenosphere are 1.03 g/cm3, 2.67 g/cm3 and 3.10 g/cm3
respectively. !
Figure 1 Simplified model of Birkbeck Margin !! f) Explain why the free-air anomaly of the Birkbeck Margin can be
calculated by adding the measured gravity anomalies of the two
half-slabs in d). Why is it not necessary to know the latitude of the
Birkbeck Margin in the calculation? !!g) By using information given in f), calculate the free-air anomaly
across Birkbeck Margin and sketch it in a graph.
!
!h
) Explain how the expected Bouguer anomaly of Birkbeck Margin
(Figure 1) will be different from the free-air anomaly. It is not
necessary to calculate or sketch the Bouguer anomaly in a
graph. !!!!i) By considering the pressure difference at 100 km below the sea
level of Birkbeck Margin (Figure 1), comment on the isostatic
equilibrium of the Birkbeck Margin. Assume that g = 9.8 m/s2 at
all depths. !!!!j)* By considering Equation 1, explain how the free-air anomaly
profile (part g) can be used to determine the isostatic status of
Birkbeck Margin.