Dynamical Changes Induced by Strong Electromagnetic Discharges in Earthquakes’ Waiting Time Distribution at the Bishkek Test Area (Central Asia)

From 1 August 1983 to 28 March 1990 at the Bishkek electromagnetic (EM) test site (Northern Tien Shan and Chu Valley area, Central Asia), strong currents, up to 2.5 kA, were released at a 4.5 km long electrical (grounded) dipole by discharge of MHD or large batteries. This area is seismically active and a catalogue with about 14100 events from 1975 to 1996 has been analyzed. The seismic catalogue was divided into three parts: the first, 1975–1983, with no EM experiments; the second, 1983–1988, during EM experiments; and the third part, 1988–1996, after the experiments. Qualitative and quantitative time series non linear analysis was applied to waiting times of earthquakes to the above three sub-catalogue periods. Qualitative and quantitative methods used include iterated function systems (IFS), Lempel-Ziv algorithmic complexity measure (LZC), correlation integral calculation, recurrence quantification analysis (RQA), and Tsallis entropy calculation. General features of temporal distribution of earthquakes around the test area reveal properties of dynamics close to low dimensional non-linearity. Strong EM discharges lead to the increase of extent of regularity in earthquakes’ temporal distribution. After cessation of EM experiments, the earthquakes’ temporal distribution becomes much more random than before the experiments. To avoid non-valid conclusions, several tests were applied to our data set: differentiation of the time series was applied to check the results that were not affected by non-stationarity, followed by surrogate data approach in order to reject the hypothesis that dynamics belongs to the colored noise type. Small earthquakes, below the completeness threshold, were added to the analysis in order to check the robustness of the results.