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.

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