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Reservoir Induced Seismicity near Heron and El Vado Reservoirs, Northern New Mexico, and Implications for Fluid Injection Within the San Juan Basin


Spatial, temporal and Previous HitmagnitudeNext Hit-frequency relationships for earthquakes occurring between 1976 and 1984 near Heron and El Vado reservoirs in northern New Mexico are examined for evidence of reservoir-induced seismicity (RIS). Most of the 264 located shocks, including those with the highest Previous HitmagnitudeNext Hit (mb = 3.8), occurred in 1982 when Heron reservoir reached its maximum capacity of approximately 0.5 km3 and an impoundment depth of 66 m. More recent data obtained with EarthScope's transportable array suggests seismicity is continuing below the reservoirs. Between 1976 and 1984 earthquake swarms followed, or were enhanced by, reservoir filling where filling resulted in new maximum water volumes for Heron reservoir. Shocks generally cluster between the reservoirs in a region of north-south block faulting. A cumulative earthquake frequency versus Previous HitmagnitudeTop plot for Heron-El Vado produced a “b-value” of 0.92 +/− 0.03 (1 SD) which is slightly higher than other b-values for northern New Mexico, and is consistent with b-values for reservoir-induced shocks in other areas. The spatial and temporal distribution of these events, along with their b-value, suggests most of them have been triggered by reservoir loading and elevated pore pressure. Practical implications are that RIS can occur in reservoirs with impounded water depths of less than 100 m – thus these formations may be acutely sensitive to waste fluid injection in the San Juan basin. Also, hydraulic diffusivity is are quite high, suggesting seismicity may onset almost immediately after an injection event.