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Characterizing time-dependent deformation and fracturing in rocks is crucial for assessing seismic hazards and related risks. An important aspect of this process is subcritical fracture growth (SFG) and its properties. Under SFG, fractures can grow at stress values lower than the critical fracture toughness. Many laboratory studies have focused on tensile SFG, and some have assessed shear SFG in rocks. Here, we provide evidence for mixed-mode (tensile and shear) SFG in injection-induced seismicity in a geothermal field. We study a relationship between the SFG parameters and the rate of water injection into the reservoir. We analyse the injection rate with the degree of 3D stress anisotropy and find that the SFG regime may be controlled by the degree of the stress asymmetry, i.e., how close intermediate stress is to a transversely anisotropic condition. We observe that a critical rupture occurs when both SFG parameter is higher than 2 and the principal stresses are symmetric. We present a possibility of using these results in the operational reservoir to manage the seismic hazard.This work was supported under the S4CE: "Science for Clear Energy" project, which has received funding from the European Union's Horizon 2020 research and innovation programme, under grant agreement No 764810. The work was also partially supported by statutory activities No 3841/E-41/S/2018 of the Ministry of Science and Higher Education of Poland. [ABSTRACT FROM AUTHOR]