Study on Nonlinear Elastic Behavior in Diurnal Surface Velocity Variations Caused by Temperature Using Distributed Acoustic Sensing (DAS)

High temporal resolution seismic velocity variations are crucial for detecting potential small precursor signals before hazardous geological events, thus aiding in the prediction of catastrophic geological events. Therefore, the study of the mechanisms underlying high temporal resolution seismic velocity relative variations (dv/v) is of great importance. Using a Distributed Acoustic Sensing (DAS) array, we obtain diurnal dv/v variation curves through coda wave interferometry (CWI) and carefully analyze potential environmental factors that might affect velocity. We find that as the thermal strain rate decreases, dv/v shows a significant increasing trend, while as the thermal strain rate increases, dv/v shows a decreasing trend. In ultrasonic laboratory experiments on rocks, we observe similar patterns during thermal cycling of the rocks. Based on previous studies, we believe that this phenomenon is due to the inherent nonlinear elastic properties of rocks. Using higher-order nonlinear elastic parameters, we successfully reconstruct the trends in near-surface dv/v variations and analyze the underlying physical mechanisms. We recommend that observations of seismic velocity variations be interpreted within the framework of nonlinear elasticity.