Figure 2

Temporal evolution of (a) injection pressure drawn as a continuous black line together with the magnitude of seismic events, which are represented by circle symbols. The diameter of the circles are scaled with the magnitude and the colors differentiate the responses from the different HF experiments; (b) normalized strain \({\epsilon }^{\ast }=\epsilon /{\boldsymbol{std}}(\epsilon )\) [-] for two selected strain sensors located in both S1 and S3 shear zones. Strain has been normalized by its standard deviation to better appreciate the shapes of both time series. Positive values indicate compressional regimes, while negative values indicate extensional regimes; (c) fracture discharge rates monitored at the GE-MIMS station. The horizontal dashed line represents the average discharge rate prior to stimulation; (d) relative changes in He/N₂ from background [%] and (e) relative changes in Ar/N₂ from background [%]. The background average ratio in He/N₂ and Ar/N₂ are shown as blue squares. Background error bars are 2σ and represent the typical analytical error. Time series of raw data are shown as blue triangles, and low-pass filtered ratios are represented by magenta lines. The different stimulation experiments are labeled with HF# at the top of the figure. Colored triangles in subpanel c identify the peaks in He/N₂ concentrations following each HF# experiment, which are further analyzed in Fig. 3.