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GEO3010 (Geophysics); Spring 2016; final exercise
*Visit FASB 271 to check your grade.
*The final exam will be held at FASB 250 8-10 am on 4/29 (Friday).
*No class on Wednesday 4/27 (Reading day)
*One question from the midterm will be asked in the final exam.
1. Normal magnetic materials lose their magnetic property at ~500 °C. For a location
with heat flux ~50 mW/m2 and thermal conductivity ~2.5 Wm-1K-1, estimate the depth
when induced magnetism diminishes.
2. For a spherical density anomaly shown below, sketch the gravity anomaly observed on
the surface. Estimate the gravity anomaly observed at B. The volume of a sphere is
4/3πr3 and the gravitational constant is 6.67× 10-11 m3 kg-1 s-2.
3. Assuming the density structure across the Snake River Plain can be simplified as the
following plot and the system reaches isostatic equilibrium, (a) estimate the
topographic difference between location A and B. Estimate the gravity acceleration
difference between location A and B (b) before any correction, (c) after free air
correction, and (d) after both free air and Bouguer corrections. (e) Assuming that the
low topography of Snake River Plain eventually is removed due to sedimentary
deposit (density ~2700 kg/m3), what will be the crustal thickness then?
Information that might be helpful:
Gravitational constant G=6.67384 × 10-11 m3 kg-1 s-2
Earth radius 6371 km
Earth mass 5.972×1024 kg
The gravitational acceleration perturbation due to an anomalous density layer with lay
thickness t.
4. As shown in the plot below, a paleomagnetic material is buried underneath the surface
at a location near the equator. Sketch the magnitude of the magnetic field near surface
from south to north across the location if the magnetic dipole is oriented in the (a)
South-North or (b) up and down direction.
5. For a porous medium tube filled with water shown below, calculate the overall
resistance assuming (1) the resistivity of water is 10 ohm-m and shale is 100 ohm-m
and (2) the cross section area of water is 1 m2 and the cross section area of shale is 4
m2 .