Canada and China host some of the most severe cases of hydraulic-fracturing (HF)–induced seismicity related to unconventional shale gas development. Three main mechanisms have been proposed to explain earthquake triggering during HF operations: pore-pressure diffusion, poroelastic stress perturbations, and aseismic slip, which can act individually or in combination. Although elevated pore pressure has been long recognized as the primary triggering mechanism, tracking pore-pressure evolution on seismogenic faults and quantifying its role in the nucleation of moderate-to-strong earthquakes remain challenging during active injection. Here, we first apply a non-tomographic Vp/Vs approach (Lin and Shearer, 2007) to the Sichuan Basin, China and obtain near-source Vp/Vs values with high spatiotemporal resolutions of ~2 days and 150 m by utilizing clustered induced seismicity and dense seismic arrays. We observe increases in Vp/Vs from ~1.73 to ~1.80 on seismogenic faults approximately 5–10 days prior to moderate earthquakes, suggesting a process of pore pressure build-up that ultimately initiates seismic slip. To investigate whether the HF-induced seismicity in Canada and China exhibits similar spatial or temporal Vp/Vs patterns associated with M>3 earthquakes, we apply this approach to the 2021-2025 earthquake catalogue in the Montney formation in Northeast British Columbia. Our in-situ Vp/Vs results provide a potential near-real-time monitoring strategy for assessing fluid pressure variation and seismic hazard during active HF operations.