## 6 Discussion
### Triads
The red line is obtained by averaging over a sliding window of 20 min, with the step 1 min. We see that mirror triads are relatively rare phenomenon. They appear about an order of magnitude less frequently than classical triads. To make the picture of mirror triads more visual, we will show Figure 6. It shows mirror triads in the range of main shocks magnitude \(5\leq M_{0}<6\). Here \(N_{-}=4189\), \(N_{0}=2430\), \(N_{+}=201\). **GTS. ** So, we found that there is a rare but rather interesting subclass of tectonic earthquakes, in which the number of aftershocks in the interval of 24 h after the main shock is significantly less than the number of foreshocks in the same interval before the main shock. In many cases, there are no aftershocks at all. We asked the question: Are there earthquakes with magnitudes \(M_{0}\geq 6\), neither before nor after which there are neither foreshocks nor aftershocks? The search result was amazing. We have discovered a wide variety of this kind of earthquake and named it _Grande terremoto solitario_ (Italian), or GTS for short [47]. In Figure 7, we see that the number of GTS (2460) is approximately equal to the number of classical triads (2398). GTS arise spontaneously under very calm seismic conditions and are not accompanied by aftershocks. This suggests an analogy between the GTS and the so-called \"Rogue waves\" (or \"Freak waves\")--isolated giant waves that occasionally emerge on a relatively quiet ocean surface (e.g., see [48]). This analogy may prove to be quite profound, since the spontaneous occurrence of pulses with anomalously high amplitudes is a common property of the nonlinear evolution of dynamic systems [49]. Figure 6: Time distribution of foreshocks and aftershocks of mirror triads in the range of magnitudes of the main shocks \(5\leq M_{0}<6\). Figure 7: Solitary earthquakes with magnitudes \(M_{0}\geq 6\). For completeness, we also present the data for the symmetric triads in which \(M_{0}\geq 6\) and \(N_{+}=N_{-}\): \(N_{-}=186\), \(N_{0}=121\), \(N_{+}=186\). It is interesting to note that, formally, GTS can be related to a variety of symmetric triads, since for them \(N_{+}=N_{-}=0\). **Activation factor. ** Figures 5 and 6 shows that foreshocks in the mirror triad appear to have a temporal distribution similar to the Omori distribution for aftershocks in the classical triad. Let us dwell on this in more detail. We represent the classical Omori law [1] in the simplest differential form  
\[\dot{g}=\sigma_{+}. \tag{25}\]  
Here \(g=1/n\), \(n(t)\) is the frequency of aftershocks, \(t>0\), the dot above the symbol means time differentiation, \(\sigma_{+}\) is the so-called deactivation factor of the earthquake source, \"cooling down\" after the main shock (see [3; 8; 21]). Suppose that for foreshocks of the mirror triad, the evolution law (25) is fulfilled with the replacement of \(\sigma_{+}\) by \(\sigma_{-}\). It is natural to call the \(\sigma_{-}\) value the activation factor. In this paper, we will limit ourselves to presenting the interesting Figure 8. It shows the generalized evolution of foreshocks and aftershocks in symmetric triads satisfying the condition \(5\leq M_{0}<6\). Here \(N_{-}=1050\), \(N_{0}=742\), \(N_{+}=1050\). The top panel shows an amazing mirror image. In the bottom panel, we have shown the variations of the \(\sigma_{-}\) and \(\sigma_{+}\) functions as the first step towards studying the activation and deactivation coefficients of an earthquake source in mirror triads. (For the procedure for calculating \(\sigma_{\pm}\), see [8]). **Origin of mirror triads. ** In conclusion of this section, we would like, with all the necessary reservations, to express a careful judgment on the question of the origin of mirror triads. Let us assume that a system of faults in a certain volume of rocks is under the influence of a slowly growing total shear stress \(\tau\).