Seismic Moment Evolution During Hydraulic Stimulations

Session: Mechanisms of Induced Seismicity: Pressure Diffusion, Elastic Stressing and Aseismic Slip
Type: Oral
Date: 4/29/2020
Time: 08:45 AM
Room: 215 + 220
Description: 

What allows and controls seismic events to grow during hydraulic stimulations? Predicting and managing the size of earthquakes caused by fluid injection is currently the major concern of many projects associated with geothermal energy production. Recent reports on the hydraulic stimulation of the deepest enhanced geothermal system to date have shown at least a potential to control the magnitude of the occurring seismicity. This potential stands in contrast to a long history of geothermal projects which failed or were abandoned due to large induced earthquakes. Here, analysis of past and present stimulation projects reveals that the temporal evolution and growth of maximum observed moment magnitudes may be linked directly to the injected fluid volume and hydraulic energy. Overall evolution of seismic moment seems independent of the tectonic stress regime and is most likely governed by reservoir specific parameters, such as the preexisting structural inventory. Data shows that magnitudes can grow either stable, indicating the constant propagation of self-arrested ruptures, or unbound, for which the maximum magnitude is only limited by the size of tectonic faults and fault connectivity. Transition between the two states may occur at any time during injection or not at all. Monitoring and traffic-light systems used during stimulations need to account for the possibility of unstable rupture propagation from the very beginning of injection by observing the entire seismicity evolution in near-real-time and at high resolution for an immediate reaction in injection strategy.

Presenting Author: Stephan Bentz

Authors