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Magnetic reconnection associated with the tearing instability occurring indouble-current sheet systems is investigated within the framework of reducedresistive magnetohydrodynamics (MHD) in a two-dimensional Cartesian geometry.The explosive non linear phase is particularly explored using the adaptivefinite-element FINMHD code. The critical aspect ratio, that is defined as theminimum $L/x_s$ ratio (with $L$ and $x_s$ being the periodic system length andhalf-distance between the two current layers respectively) necessary for nonlinear destabilization after the linear and early non linear saturation phases,is obtained. The latter threshold is independent of the details of the choseninitial equilibrium (double Harris-like magnetic profile) and of theresistivity. Its value is shown to be $4.7$, that is close and slightly smallerthan the value of order $5$ deduced using a more particular equilibriumconfiguration in previous studies. The time dependence of the kinetic energy($E_K$) is shown to follow a double exponential law, $E_K \propto \exp \[e^{(\gamma^* t)} ]$, with a pseudo-growth rate $\gamma^* \simeq 0.1 \ t_A^{-1}$ ($t_A$ being the characteristic Alfv\'en time) that is again independentof the configuration and resistivity. The mechanism offers a possibleexplanation for the sudden onset of explosive magnetic energy release occurringon the fast Alfv\'en time scale in disruptive events of astrophysical plasmaswith pre-existing double current sheets like in the solar corona.

On the explosive phase of the tearing mode in double current sheet  plasmas: effect of the equilibrium magnetic configuration on the onset  threshold and growth rate