Laboratory measurements anomalous 0.1-0.5 Hz streaming potential under geochemical changes: Implications for electrotelluric precursors to earthquakes

Streaming potentials resulting from flow of various salt solutions in rock were measured on saturated sediments (Fontainebleau sandstones). The streaming potential ∃V was found to be proportional to the driving pore pressure ∃P. Pulses of amplitude 15-40 mV in the frequency range of 0.1 to 0.5 Hz were observed when the conductivity of the injected water was decreased and the fluid flow rate was relatively low, corresponding to a Darcian velocity of 17 to 30 cm/h. The amplitudes of these pulses are 47% to 133% of the corresponding steady components of the ∃V values. Such geochemically induced effects may possibly be responsible for the frequency signals from 0.1 to 0.5 Hz that were sometimes observed before an earthquake.