Directional hydraulic fracturing is widely applied to mitigate seismicity hazards in multilayered thick hard roof (THR) systems. To clarify the governing mechanisms and effectiveness of various fracturing layouts, a field-scale Finite Discrete Element Method model was developed with stratum-specific in-situ stress loading. The effects of fracturing horizon, spacing, and inclination on roof caving behavior during mining were analyzed. The effectiveness of seismicity mitigation was further evaluated by correlating abutment stress evolution with seismic energy release characteristics. Findings indicate that pre-fracturing in lower THR significantly enhances roof fragmentation and stabilizes abutment stress evolution. Compared to the baseline without pre-fracturing, smaller fracture spacing combined with vertical fracture facilitates a transition from sudden violent failure to stepwise progressive breakage, effectively lowers the abutment stress and the number of high-energy seismic events (E > 104 J) by 4.22% and 38.46%, respectively. For the upper THR, the combination of moderate fracture spacing and low inclination angle provides the best performance for seismicity mitigation among the simulated schemes. This configuration increases the energy released during roof caving and reduces the number of high-energy events by 7.69%, indicating a less intense roof caving process. The results further reveal a layer-dependent fracture-layout principle, in which small-spaced vertical fractures are preferred for the lower THR, whereas moderate-spaced inclined fractures are more suitable for the upper THR. These findings provide mechanistic insights and practical guidance for optimizing directional hydraulic fracturing layouts in THR.