Formation Conditions for Nanoparticles in a Fault Zone and Their Role in Fault Sliding

• Published in: Tectonics (Washington, D.C.) D.C.), 2019-01, Vol.38 (1), p.159-175
• Main Authors: Cai, Zhou‐rong, Lu, Li‐juan, Huang, Qiang‐tai, Li, Jian‐feng, Zhong, Li‐feng, Xiang, Jun‐yang, Xia, Bin, Liu, Hai‐ling
• Format: Article
• Language: English
• Subjects: Experiments; Fault lines; fault sliding; fault zone; Fault zones; formation condition; formation mechanism; Friction; High temperature; Low temperature; nanoparticle; Nanoparticles; Pressure; Rivers; Shear zone; Simulation; Slumping; Temperature effects
• ISSN: 0278-7407; 1944-9194
• DOI: 10.1029/2018TC005171

Recent high‐velocity rotary shear experiments results show that spherical nanoparticles can reduce fault friction dramatically during seismic slip. But questions like what are the roles of the nanoparticles in the whole slip are largely open problems. In this study, two types of nanoparticles were found in the Red River fault zone, including agglomerated nanoparticles in the ductile shear zone and spherical nanoparticles adjacent to the brittle faults. To ascertain the formation of these nanoparticles and explore the role of nanoparticles, the experiments under high temperature and pressure were conducted. The results of the experiments and of the previous studies suggest that the spherical nanoparticles can produce at the low temperature, which may lubricate the fault and significantly reduce the dynamic coefficient of friction. With the rise in temperature, the spherical nanoparticles are elongated or deformed to the agglomerated nanoparticles, which may no longer lubricate the fault, and lead the fault slip to slow down until it stops. Accordingly, this paper summarizes the role of these nanoparticles throughout the whole process of fault sliding. Plain Language Summary Nanoparticles are widely found in the nature ductile shear zone and experimental faults, but there is controversy on their formation; it is still not clear how the nanoparticles affect the fault for the entire process of sliding. In this paper, two types of nanoparticles were found in the Red River fault zone, including agglomerated viscoplastic nanoparticles and spherical nanoparticles. Based on these findings, we carry out simulation experiments under high temperature and pressure, to ascertain the formation conditions of these nanoparticles and explore the role of nanoparticles during the entire fault sliding. The results of the simulation experiments and of the previous friction experiments, reveal that two types of nanoparticles are formed in different temperature and pressure, which maybe play different roles (weaken or strengthen the fault) in the whole sliding. Specifically, at the onset of sliding, spherical nanoparticles are formed and acted as dynamic weakening to lubricate the fault. With the temperature rising, spherical nanoparticles are transformed into agglomerated viscoplastic nanoparticles, and dynamic friction increases. The agglomerated viscoplastic nanoparticles may be the primary reason for an increase in the dynamic friction, and even a halt to the fault during a l