Earthquakes Induced by Wastewater Injection, Part I: Model Development and Hindcasting

In the past decade, several parts of Central United States, including Oklahoma, have experienced unprecedented seismicity rates, following an increase in the volumes of wastewater fluids that are being disposed underground. In this paper, we present a semi-empirical model to hindcast the observed seismicity given the injection timehistory. Our proposed recurrence model is a modified version of the Gutenberg-Richter law, building upon the Seismogenic Index model, which predicts a linear relationship between the number of induced events and the injected volume. Our methodology is grid-independent and accounts for the effects of spatio-temporal pore-pressure diffusion, the stressing-rate dependency of the time-lag between injection and seismicity rate changes, and the rapid cessation of seismicity upon unloading. Although the model is generic in order to be applicable in any region and has essentially only two free parameters for spatial calibration, it matches the earthquake time-history of Oklahoma well across various scales, for both increasing and decreasing injection rates. In the companion paper (Grigoratos et al., 2020a), we employ the model to distinguish the disposal-induced seismicity from the expected tectonic seismicity and test its forecasting potential.