The control of fault contact heterogeneity on the nucleation process of stick slip instability of meter scale faults
Fault heterogeneity is an important characteristic of natural faults.In order to simulate seismic instability processes in the field,we conducted stick-slip experiments using heterogeneously contacted precut meter-scale rock faults.We observed the spatial and temporal evolution of strain in multiple stick-slip events and compared it with measurements of fault contact heterogeneity.We demonstrate that the weak contact segment of the fault exhibits the earliest pre-slip,and thus serves as the initiation region for nucleation.As the instability approaches,the pre-slip area expands and the slip rate increases.In comparison to centimeter-scale homogeneous faults,the pre-slip extension during the quasi-static process is minimal,while the transition to the quasi-dynamic process is sudden and rapid.We also find that the strong contact segment of the fault remains locked throughout the nucleation stage,with stress continuously building up.As the impending instability approaches,strain concentration gradually increases.The yielding of the strong section marks the moment when the fault rupture rate shifts from slow to fast.Sustained locking within strong contact segments is relatively uncommon in stick-slip experiments of centimeter-scale homogeneous fault.In addition,the loading rate as well as the loading history are important factors affecting the duration of nucleation on meter-scale faults.Slower loading rates result in longer nucleation durations,while extended loading histories tend to homogenize faults and subsequently reduce nucleation durations.The aforementioned studies yield explicit evidence that the spatial distribution of fault contact heterogeneity has a direct influence on the spatial and temporal progression of the nucleation process.These findings not only contribute to applying experimental results to operational earthquake forecasting practices,but also facilitate the exploration and comprehension of earthquake precursor mechanisms,particularly those related to continental shallow sources.
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