## 5 Implications for Nucleation of Continental Earthquakes  
It has long been known that earthquake activity is a symptom, if not the agent, of active tectonics. The cyclic nature of earthquakes, as described by [PERSON] (2006), depends on the schizosphere, plastosphere, and asthenosphere. This coupling of mechanical processes across these distinct layers influences the timing and magnitude of seismic events. Three primary models of strain accumulation exist, each differing significantly in how the schizosphere and plastosphere are coupled and their relative strengths. In the viscoelastic coupling model, the fault traverses the schizosphere but does not extend into  
Figure 5: Schematic diagram of our sample summarizing the relationship between steady-state shear strength (or friction coefficient), its rate dependence, and the dominant deformation mechanisms and associated microstructures as a function of sliding velocity (V) and temperature (T), as predicted by the CNS model [74]. Figure reproduced from [9] with permission. Figure 6: Comparisons between numerical and experimental results of (**a**) steady-state friction coefficient and (**b**) frictional stability parameter (\(a-b\)) for simulated granite gauges at sliding velocities of 0.01–10 \(\upmu\)m/s under wet conditions [37; 93; 94]. Figure reproduced from [92] with permission. the plastosphere, which is modeled as a viscous layer [95; 96]. However, the strong plastosphere model suggests the fault is weak, and the plastosphere is strong; in that case, the plastosphere drives all systems during interseismic processes [97]. In the deep slip model, the fault may be active through both the schizophre and plastosphere, being seismogenic in the schizophre and aseismically slipping in a ductile shear zone, weaker than the bulk plastosphere, in the lower crust. In this model, the deep shear zone loads the schizosphere during the interseismic period, and the deeper zone is subsequently reloaded by the coseismic slip [98]. The deep slip model explored by [PERSON] and [PERSON] [99] not only provides more comprehensive details than earlier formulations but also accounts for several key characteristics documented in prior studies. This model investigated how the slip is distributed throughout repeated loading cycles on a fault governed by the RSF law (Equations (1)-(4)), using parameters derived from laboratory experiments. The values they used for the velocity dependence friction term (\(a-b\)), with the temperature gradient they assumed, predict a transition to a stable slip at \(11\) km (as (\(a-b\)) values transition from negative to positive) (Figure 7). To our knowledge, the formation of seismological zones is linked to the thermomechanical and hydrological conditions within the lithosphere. Variations in temperature (\(T\)), normal stress (\(\sigma_{n}\)), slip rate (\(V\)), shear displacement (\(S\)), and pore fluid pressure (\(P_{t}\)) can significantly alter the mechanical properties and rheological behavior of both the brittle upper crust (schizosphere) and the underlying ductile lower crust or upper mantle (plastosphere). The experimental results on quartz-rich and granitic gauges indicate that with increasing \(T\)s, fault slips exhibit VW behavior (\((a-b)<0\)) at intermediate \(T\)s (\(\sim\)100-400 \({}^{\circ}\)C), corresponding to mid-crustal depths (\(\sim\)4-16 km), suggesting stable slips for earthquake nucleation. In contrast, at both lower and higher \(T\)s, the fault shows VS behavior (\((a-b)>0\)), indicative of stable sliding (Figure 5, A). However, the \(T\) range of the intermediate VW regime is not fixed; increasing the V tends to shift the transition from the VW to VS regime toward higher \(T\)s (Figure 5, A). This is likely due to the reduced time available for thermally activated deformation mechanisms at higher strain rates. In contrast, elevated \(P_{t}\) facilitates all three frictional regimes toward lower \(T\)s (Figure 5, B), a result consistent with the reduction in effective normal stress and hence frictional resistance.