Moment Partitioning for Injection-Induced Seismicity: Case Studies and Insights from Numerical Modeling

Abstract

In order to understand and mitigate felt seismicity induced by fluid injection activities such as Enhanced Geothermal Systems, it is important to know what controls the seismic response to the injection of a certain volume. A recent study proposed an upper bound to induced magnitudes that can be expected based on injected volume and shear modulus. However, this upper bound is mostly not released during injection. The physical controls on the measure of the seismic moment release with respect to this theoretical maximum are yet unknown. In this study we investigate the moment partitioning (the ratio of observed moment to the predicted moment which is a function of volume and shear modulus) of injection sites worldwide and compare it against various site specific and injection parameters. In addition, for a select number of sites we track the moment partitioning as a function of injection time. With a coupled hydro-mechanical model we model the seismic response for a generic injection case and are able to reproduce some of the main trends observed in the case studies.