Induced Seismicity And Earthquake Hazard Mitigation By Electromagnetic Impact of MHD Generator

Some field and laboratory data reveal possibility of significant coupling of elastic and electromagnetic (EM) fields. Laboratory experiments related to the electromagnetic initiation of mechanical instability (slip) and EM and mechanical control of slip process are presented. For initiation of slip series of strong EM pulses were applied to the mechanical system driven close to the critical state, namely, to the (dry) rock samples (basalt), placed on the inclined supporting sample at the slope angle less than, but close to the critical slip angle. It has been found that when the EM field is parallel to the slip plane the EM impact initiates the slip with the probability P<0.07 at the voltage Δ V=1300V and with the probability P<0.2 at Δ V=10kV. On the other hand, if the EM field is normal to the slip surface, application of EM pulse hampers the slip. We also try to prove experimentally the possibility of controlling slip regime by relatively weak periodic mechanical or EM impact, in the way it is done in the nonlinear dynamics experiments on controlling chaos. Weak periodic mechanical or electrical perturbations were superimposed on the system in order to find the conditions that allow the control of slip. Quite different regimes of slip were excited depending on the amplitude and the frequency of applied weak perturbations. The observed regimes of slip vary from the perfect synchronization of slip events, recorded as acoustic emission bursts with the perturbing periodic mechanical or EM impact to their complete desynchronization. We consider the obtained results as evidence that it is possible to control slip by the application of weak periodical perturbations. The phenomenon can be explained in terms of the nonlinear dynamics and synchronization theory. Nonlinear analysis of waiting time series shows that fractal dimension and b-value increase with intensity of applied electrical field. We conclude that our laboratory experiments give a sound principal basis for the interpretation of the field data on the control of seismic regime by relatively weak natural or artificial perturbations; of course, in the earth crust the detailed physical mechanisms of coupling between tectonic forces and superimposed perturbations may be different.