Towards an improved understanding of induced seismicity associated with hydraulic fracturing

Sparked by a number of recent high-profile incidents of seismic events felt on the surface near petroleum field operations, there has been growing concern over seismic hazards associated with hydraulic fracture stimulation and injection programmes. In response, several jurisdictions have enacted regulations requiring modification or temporary shut-down of operations in treatment wells close to earthquakes which exceed certain magnitude thresholds. These recently proposed magnitude-based ‘traffic light’ systems that break from existing standards and regulations related to seismic hazard, which are typically based on measured ground shaking (velocity and acceleration). Observed shaking, and the associated risk of damage or injury, is determined by several factors including both earthquake source characteristics and site- and raypath-specific conditions. Additionally, the ground motion, and associated hazard, produced by injection-induced seismicity is variable for events of the same magnitude, owing to differences in stress release behaviour and source depth. Ground shaking is directly measured by seismic instruments and directly related to building codes and structural design specifications. To achieve a more consistent and reliable regulatory standard, we suggest that regulations be based on ground motion, rather than magnitude, for the evaluation of seismic hazards associated with injection-induced seismicity.