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Figure 6.17 The backpropagating wave fields (for the three snapshots shown in Figure 6.16) generate seismoelectric current
sources at many locations characterized by appropriate contrasts of physical properties. The seismoelectric source is thus distributed
in space and time, which creates a strong interpretation ambiguity. However, at the focusing time, the seismoelectric current
source is mostly localized in space, and it is stronger than at other times. We don
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t plot the scale of the seismoelectric current
source here because they depend on the intensity of the seismic source.
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Figure 6.18 Electrical potential observed as a function of time for the seismoelectric sources depicted in Figure 6.17, corresponding
to the three snapshots shown in Figure 6.16. Interpretation of this potential is ambiguous, given that the seismoelectric source
is distributed in space and time. In our method, only the potential seen in the rightmost frame is relevant, and its interpretation
is not ambiguous since in this case we deal with a known position and time of the source. We don
t plot the scale of the electrical
potential because they depend on the intensity of the seismic source. The only thing that matters is that the strength of the
electrical potential is recordable at the electrodes located in the two wells. The gray-filled circle corresponds to the position
of the electrodes at which the potential is recorded at the time of focusing.
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