Earthquake Sources: Finite Fault Sources

We investigate electromagnetic responses to a finite fault due to electrokinetic effect. The finite fault is discretized into a series of small subfaults, each of which is taken as a point source with different initiation time. The wave fields generated by the whole fault are then synthesized by stacking those generated by all the subfaults. Numerical results show that the rupturing fault generates two types of electric field variations, the coseismic oscillatory and postseismic decaying variations. When the fault rupturing stops and the seismic waves pass far away, the magnetic field vanishes while the electric field remains, decaying slowly and lasting for hundreds of seconds. Adjacent to the free surface, the vertical electric field is about one hundred times larger than the horizontal one. When the receiving depth increases, the amplitudes of the horizontal electric fields in both the oscillatory and decaying components increase while those of the vertical electric fields decrease.