## 1 Introduction  
Earthquakes on crustal faults are dominated by granitoid gouges, which mostly range between depths of 2 and 18 km and provide information about the location and style of deformation of the fault in this upper-crustal \"seismic\" zone (e.g., the San Andreas Fault). With increasing temperature (depth), the frictional (brittle)-viscous (ductile) transition in these fault gouges plays a crucial role, as it represents a significant shift in the rheological behavior of the Earth's lithosphere. This transition also aids in defining the lower limit of the seismogenic zone, which is the region where large-magnitude earthquakes typically initiate [1, 2], such as the depth distribution of earthquakes in the central creeping section of the San Andreas Fault [3, 4, 5], the Kellyland Fault in eastern Maine [6], the Alpine Fault in New Zealand [7], and the Alps Fault [8], as well as the Anninghe-Xianshuihe Fault zone on the southeastern boundary of the Tibetan Plateau [9,10]. Understanding the depth distribution and sliding characteristics of seismogenic zones is crucial, as it not only delineates where large-magnitude earthquakes are likely to initiate but also provides insights into the diverse slip mechanisms that characterize fault zones. Nevertheless, the direct observation of fault mechanics at seismogenic depths remains technically challenging due to the extreme in situ conditions. In this context, laboratory friction experiments provide a valuable approach to simulate and systematically investigate the physical and chemical processes that control fault strength and stability under controlled temperature, pressure, pore fluid, and slip rate conditions that are representative of various depths within the continental crust. Fault slip events can span a range of scales, from a few millimeters to several hundred kilometers, and occur over time scales ranging from fractions of a second to millions of years, which causes the distribution of slip thickness on field faults to range from \(\sim\)1 mm to 1 cm [11,12]. A complex multi-mode slip is associated with various types of earthquake phenomena [13], including regular earthquakes [14], slow-slip events [15,16], low-frequency earthquakes [17,18], episodic tremor and slip [19], and aseismic creep [20,21]. In terms of crustal deformation, the loading cycle is often divided into four phases, preseismic,oseismic, and interseismic, called the earthquake periods. The concept of the seismic cycle was first formalized by [PERSON] [22], who proposed the elastic rebound theory based on his investigation of the 1906 San Francisco earthquake along the San Andreas Fault. According to this model, tectonic motion causes elastic strain to accumulate on faults locked by friction until failure occurs, and stored energy is suddenly released during an earthquake [23]. While this conceptual framework provides a first-order understanding of earthquake occurrence, the detailed physical processes governing strain accumulation, fault strength, and instability remain incompletely understood. Laboratory friction experiments offer a controlled means to investigate these processes by replicating the stress conditions, slip behaviors, and microstructural evolution of fault zones, thereby providing empirical constraints on the mechanics of the seismic cycle at different depths. [PERSON] and [PERSON] [24] developed the adhesion friction theory, which revolutionized the understanding of the frictional behavior of stick-slip instability at the microscopic level. [PERSON] and [PERSON] [25] inferred that the recurrence of stick-slip could be a possible mechanism for shallow-focus earthquakes. Moreover, studies on the preseismic period focus on the analysis of frictional weakening or strengthening before failure, the development of nucleation zones, and the study of slow-slip events [26,27,28].