Figure 5
From: Stress transfer outpaces injection-induced aseismic slip and triggers seismicity
Seismicity induced by hydraulic fracturing operations in Shuangshi Town, Zigong City at the Weiyuan shale gas field in Sichuan Basin, China. (a)–(d) Map view of seismicity on Day 3, 6, 13 and 23 during hydraulic fracturing, when Well Pad Z201H2 (shown by the hexagon, and horizontal wells are denoted with brown lines extending from the well pad) was in operation. A length bar of 1 km is shown for scale. F1, F2 and F3 denote the three fault segments along which most of the earthquakes occurred during this time. C1 denotes the cluster of seismicity that does not apparently fit the diffusion front, and also migrates faster than most other earthquakes in this sequence. (e) Seismicity migration pattern shown as the distance from the first earthquake over time. The blue curve is the pore pressure diffusion front with hydraulic diffusivity 0.25 m\(^2\)/s. A red dotted line with speed 250 m/day fits earthquakes that migrate faster than the diffusion front after 5 days, and is possibly an indicator of the aseismic slip front. Two more red dotted lines with migration speeds of 500 and 800 m/day are shown to fit seismicity that cannot be explained by either pore pressure diffusion or the aseismic slip front.
