Question

Refer to the schematic sketch given (not to scale). Assume average saturated density of oceanic crustal rocks = 3200 kg/m³, density of ocean water = 1000 kg/m³, and acceleration due to gravity = 10 m/s². The overburden pressure at a point (P) located 2 km below seabed and 4 km below the ocean surface is ________ MPa. (Answer in integer.) 

Hint:

Pressure in fluids or solids increases linearly with depth: \( P = \rho g h \). Convert depth to meters and pressure to MPa (1 MPa = 10\textsuperscript{6} Pa).

Answer 1

Correct Answer: 3

Step 1: Given data.
Depth below sea surface = 4 km = 4000 m. Thickness of ocean water = 2 km = 2000 m. Depth in rock = 2 km = 2000 m. Density of water = 1000 kg/m³. Density of rock = 3200 kg/m³. Acceleration due to gravity = 10 m/s².
Step 2: Calculate pressure due to water column.
\[ P_{w} = \rho_{w} g h_{w} = 1000 \times 10 \times 2000 = 2 \times 10^{7} \, \text{Pa} = 20 \, \text{MPa.} \] Step 3: Calculate pressure due to rock column.
\[ P_{r} = \rho_{r} g h_{r} = 3200 \times 10 \times 2000 = 6.4 \times 10^{7} \, \text{Pa} = 64 \, \text{MPa.} \] Step 4: Total overburden pressure.
\[ P_{total} = P_{w} + P_{r} = 20 + 64 = 84 \, \text{MPa.} \] Step 5: Conclusion.
Overburden pressure = 84 MPa.