Uncovering the Processes that Control Induced Earthquake Sequences

Earthquake sequences induced by fluid disposal into the subsurface show strong variability in their magnitude distributions and clustering behavior. We attempt to untangle the processes that control the occurrence and evolution of disposal-induced earthquake sequences by integrating detailed seismicity observations, pore pressure modeling, and 3D physics-based earthquake simulations. Observations of earthquake sequences in Oklahoma and Kansas include some sequences that have near-Poissonian distribution of interevent times and robust foreshock sequences, while other sequences display more typical mainshock-aftershock clustering behavior. Pore-pressure modeling shows that these behaviors correlate with the amplitude of the pore-pressure changes. Close to disposal wells where pore pressure changes are high, seismicity is controlled by both diffusion and earthquake stress interactions. Farther from the wells where pore pressure changes are lower, seismicity appears driven primarily by stress interactions. We further explore the stress and fault conditions that may allow for these diverse behaviors using an earthquake simulator, RSQSim. We find that the maximum magnitude of the triggered events depends strongly on the pre-existing stress on the fault. The roughness, distribution, and background stress state of pre-existing primary and secondary faults also likely influence the sequence behavior and is an area of ongoing work.