Full-Field Measurement of Dynamic Shear Ruptures Using Digital Gradient Sensing

Background: Laboratory earthquakes provide a controlled setting to examine rupture dynamics, such as rupture initiation, termination, speed evolution, and various patterns. However, the fracture energy of ruptures associated with different velocities and interface roughness remains unclear. Existing methods like photo-elasticity, digital image correlation, and strain gauges are crucial for observing stress fields but face challenges in capturing high stress gradients near the rupture tip. Objective: To overcome the limitations of existing stress field measurement techniques, this study aims to improve the characterization of rupture dynamics and quantify fracture energy with higher accuracy, particularly under varying rupture velocities and interface roughness. Methods: To achieve this, the digital gradient sensing (DGS) method is refined through integration with real contact area measurements to accurately characterize the rupture velocity and stress field near the rupture tip. Accuracy is validated through comparison with theoretical solutions and through integrated application with digital image correlation. The fracture energy of sub-Rayleigh and supershear ruptures is studied on interfaces with two different roughness levels. Results: The improved DGS method captures rupture tip location, velocity, and stress intensity factor with high accuracy. The parameter study shows that large field of view and large subset size are effective for capturing dynamic ruptures. Using the improved method, the fracture energy of supershear ruptures was found to be nearly equivalent to that of sub-Rayleigh ruptures for both rough and smooth faults. Conclusion: The enhanced approach enables quantitative characterization of the rupture tip, potentially enhancing the accuracy and precision of laboratory earthquake observations. Furthermore, this study acts as a reference for the future integration of various dynamic testing methods, promising to provide multidimensional insights into the complex nature of dynamic ruptures.