  A semiconductor model of rocks is shown to describe unipolar magnetic pulses,
a phenomenon that has been observed prior to earthquakes. These pulses are
observable because their extremely long wavelength allows them to pass through
the Earth's crust. Interestingly, the source of these pulses may be
triangulated to pinpoint locations where stress is building deep within the
crust. We couple a semiconductor drift-diffusion model to a magnetic field in
order to describe the electromagnetic effects associated with electrical
currents flowing within rocks. The resulting system of equations is solved
numerically and it is seen that a volume of rock may act as a diode that
produces transient currents when it switches bias. These unidirectional
currents are expected to produce transient unipolar magnetic pulses similar in
form, amplitude, and duration to those observed before earthquakes, and this
suggests that the pulses could be the result of geophysical semiconductor
processes.
