Applied Geophysics Electric Homework

Show ALL your work - Due 17 April, 1998

  1. Assuming that the magnetic permeability (u) of the earth is 1.3 x 10-6 henrys per meter and that the resistivity is 1 Ohm-meter, calculate the skin depth for a magnetic field with the following frequencies: (a) 0.15 Hz (b) 15 Hz (c) 15000 Hz

  2. Simultaneous measurements of the electric and magnetic fields at various frequencies are made using MT equipment. Again assuming that the magnetic permeability of the earth is 1.3 x 10-6 henrys/m, make a plot of effective resistivity versus effective depth using the data below.

    f
    (Hz)    		Ex
    (mV/km)    		Hy
    (gammas)
    0.00633512.57000
    0.10000103.14000
    0.31700200.50270
    127.000001 0.00126

  3. The potentials in the table below were measured using a dipole-dipole configuration of electrodes. The dipole length is 50 meters, and the current transmitted is 10 milliamps. In the table, "nr" is the number of dipole lengths between the transmitter and receiver and "nt" is the position of the transmitter in dipole lengths relative to the original position. Use this information to plot a pseudo-depth section of resistivity.

    nt
    12345
    nr
    11060.0095.5074.3053.1010.31
    218.5018.502.651.320.13
    30.530.640.420.080.02
    40.210.110.010.050.11
    50.030.010.010.030.06

    Values are Potentials in Millivolts