资源环境科技发展态势分析平台

We analyze source parameters of M-w-3.9 to -3.1 induced earthquakes during an in situ fluid injection experiment in France using the spectral ratio method based on empirical Greeds function. We choose 10 event pairs with highly similar waveforms and resolve their spectral ratios using multiple S wave windows. We find that master events ruptured meter-scale source patches with <1-mu m slip in a preexisting fracture network oriented differently from the injected plane. The temporal correlation between master earthquake occurrence and injection pressure peak and the relatively low ratio of stress drop to crustal strength suggest that both fluid pressure perturbation and aseismic deformation play important roles in inducing the earthquakes. The comparison between stress drops of induced earthquakes in the experiment and in the central United States indicates a dependency of stress drop on crustal shear strength.

Plain language summary Numerous small and moderate injection-induced earthquakes have been recorded in North America, Europe, and Asia. Here we present a detailed analysis about microearthquakes in an in situ injection-induced earthquake experiment, which provides an unprecedented opportunity to investigate the mechanisms of induced earthquakes. Our analysis illuminates meter-scale earthquake sources distributed in a network of preexisting rock fractures. The majority of induced earthquakes in our analysis happened when injection pressure reached a peak, indicating a direct response of rock fractures to fluid pressure perturbation. But the relatively low ratio of stress drop to crustal strength reveals that a very small fraction of the crustal shear strength is released by earthquakes, supporting the previous notion that fluid injection induces large aseismic deformation during the experiment.