Relationships between fault friction, slip time, and physical parameters explored by experiment-based friction model: A machine learning approach using recurrent neural networks (RNNs)

Abstract

Understanding the relationship between fault friction and physical parameters is crucial for comprehending earthquake physics. Despite various friction models developed to explain this relationship, representing the relationships in a friction model with greater detail remains a challenge due to intricate correlations, including the nonlinear interplay between physical parameters and friction. Here we develop new models to define the relationship between various physical parameters (slip velocity, axial displacement, temperature, rate of temperature, and rate of axial displacement), friction coefficient, and slip time. The models are established by utilizing Recurrent Neural Networks (RNNs) to analyze continuous data in high-velocity rotary shear experiments (HVR), as reported by previous work. The experiment has been conducted on diorite specimens at a slip velocity (0.004 m/s) in various normal stress (0.3–5.8 MPa). At this conditions, frictional heating occurs inevitably at the sliding surface, reaching temperature up to 68 °C. We first identified the optimal model by assessing its accuracy in relation to the time interval for defining friction. Following this, we explored the relationship between friction and physical parameters with varying slip time and conditions by analyzing the gradient importance of physical parameters within the identified model. Our results demonstrate that the importance of physical parameters continuously shifts over slip time and conditions, and temperature stands out as the most influential parameter affecting fault friction under slip conditions of this study accompanied by frictional heating. Our study demonstrates the potential of deep learning analysis in enhancing our understanding of complex frictional processes, contributing to the development of more refined friction models and improving predictive models for earthquake physics.