Fluid-injection control on energy partitioning during the earthquake cycle

Abstract

During an earthquake, the elastic energy stored in the Earth is released as frictional energy and radiated energy in the form of seismic waves. The partitioning of energy released during an earthquake gives an indication of the overall size of the earthquake and its potential for damage to man-made structures. Here, we perform an energy analysis of fluid-injection-induced earthquakes using a single-degree-of-freedom spring poroslider and rate-and-state friction. We show that seismic radiation can be modeled within the single-degree-of-freedom spring-slider by adding a radiation damping term. We then use it to study fluid injection and assess its effects on the energy partitioning during induced and triggered earthquakes. We find that: (1) seismic efficiency, stress drop, and total slip are directly influenced by the rate of increase in pore pressure, (2) the ratio of elastic energy stored in the skeleton to injection energy is low and is influenced by the rate of fluid injection, (3) seismic injection efficiency is also low and is lower for induced earthquakes compared to triggered ones, and (4) fluid injection leads to bigger and potentially more damaging earthquakes overall.