Home Work # 3 (02%)

Subsidence

1.     Beneath the Ghawar Field, the basement is found about 7 km beneath the surface. It is covered with sediments (3 km is carbonates and the other part is clastics).  Calculate the crustal thickness by assuming Airy Isosticy method.  Support your answer with drawing.

Hint:

Compensating depth is         80 km

Initial crustal thickness is         35 km.

Clastics sediments density is       2.60 gm/cm3

Carbonate sediment density is       2.80 gm/cm3

Crust density is               2.92 gm/cm3

Mantle density is                           3.35 gm/cm3

2.     Repeat the above calculation using densities 2.5, 2.7, 3.0, and 3.2 respectively. Also assume the compensating depth and the initial crustal thickness are 80 km. Compare between the two answers.  What is your opinion of this comparison?

Time-Average Equation

3.     You have a piece of sandstone whose fractional porosity is 0.25 and whose water-saturated velocity is 4000 m/s.

Calculate the sandstone velocity at zero porosity, its air-saturated velocity, and its ice-saturated velocity.

Hint:

Velocity of      Air is             330 m/s

Water            1500 m/s

Ice            3150 m/s

GOOD LUCK