Illuminating the Rupturing of Microseismic Sources in an Injection‐Induced Earthquake Experiment

Abstract

AbstractWe analyze source parameters of Mw −3.9 to −3.1 induced earthquakes during an in situ fluid injection experiment in France using the spectral ratio method based on empirical Green's 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‐μm 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.