Underground operations such as mining, oil and gas extraction, geothermal energy exploitation and natural gas storage often alter the stress state of the surrounding geology. These actions can induce earthquakes that are felt by nearby residents, and even cause damage. “Induced earthquakes can occur around the globe, causing damage to private and public buildings and putting lives in danger,” explains MEPHISTO project coordinator Francesco Grigoli, a senior researcher and lecturer at ETH Zurich in Switzerland. “The last notable case of induced seismicity was in South Korea in November 2017, when geothermal energy exploitation triggered an earthquake of magnitude 5.5. About 70 people were severely injured, and extensive damage was caused.” As a result, robust debates have opened up at the scientific, political and societal levels in the last few years. Furthermore, aversion to underground industrial activities has strongly increased among the public.
Improved monitoring tools
A key goal of the MEPHISTO project, undertaken with the support of the Marie Skłodowska-Curie Actions programme, was to address the potential threats that induced seismicity poses to society. By doing so, the project sought to alleviate citizens’ concerns, and increase confidence in industry. “Many geo energy projects fail because of the occurrence of induced earthquakes,” says Grigoli. “This suggests that existing tools for induced seismicity management – the so-called traffic light system or TLS – are not sufficient to ensure the safety of such industrial operations.” The MEPHISTO project recognised the need to move towards more efficient risk mitigation measures. It set out to develop new methods for monitoring microseismicity, and to integrate and test new seismicity modelling techniques. As a first step, the project focused on gaining a better understanding of the impact of fluid injection and extraction on the potential failure of pre-existing faults in the Earth’s crust. Geomechanical and statistical models were used to simulate induced seismicity in relation to different scenarios. From this, the project team was able to improve tools for microseismic monitoring. A key aim was to take account of the evolution of seismic activity, and how this might impact ongoing industrial operations. “We also developed a new seismic event location method,” adds Grigoli. “This enables us to obtain high-quality results, even with poor seismic monitoring infrastructures.” The project culminated in the testing of an advanced workflow for real-time induced seismicity risk mitigation – the advanced traffic light system (ATLS). This workflow was applied during a hydraulic stimulation experiment in Iceland.
Accurate risk management
MEPHISTO has achieved a number of important results that could have a positive impact on induced seismicity monitoring. The project was successful in its testing of a new workflow for induced seismicity risk management in a real-life case. This demonstrated its usefulness in the early identification of seismic risk. “Tests of the ATLS have shown promising results, and opened up new possibilities in mitigating some of the risks associated with underground industrial operations,” says Grigoli. “Next steps will include extensive tests of this risk mitigation workflow in different environments and industrial applications.” All monitoring tools developed within the project are now freely available to the seismological community, and can be applied to a range of situations.
MEPHISTO, seismicity, earthquake, mining, geothermal, hydraulic, monitoring