Understanding fluid-induced seismicity to mitigate the risks of man-made earthquakes

Not all earthquakes are triggered by natural causes. Some of them are the result of human activity. Induced seismicity can be caused by activities associated with gas or fluid injections and extractions from the Earth’s crust, the impoundment of reservoirs and mining. Such activities alter the regional stress field in the Earth’s crust and bring faults closer to failure. Although most man-made earthquakes are of low or moderate magnitude, the fact that affected areas are not necessarily prone to natural seismicity means that the populations and the infrastructures are not always adequately prepared. The focus of Dr. Georgios Michas’ research will be on fluid-induced seismicity. Recognizing that this phenomenon is not usually included in earthquake hazard assessments, Dr. Michas’s aim is to develop a tool that will help understand how fluids behave in the ground in order to prevent potentially dangerous practices.

Fluid-induced earthquakes are caused by either the injection of pressurized fluids into underground formations, for instance in the context of geothermal operations, water disposals, and oil and gas operations such as hydraulic fracturing, or the building up of pressure due to large amounts of water stocked in water dams. When large volumes of fluid are injected into the ground, some of it may infiltrate active faults and disrupt the natural forces holding the rock together. This can cause a sudden slip that releases stored energy, potentially triggering an earthquake. “ Pressurized fluids can act as lubricant, so the fault can slip more easily ”, explains Dr. Georgios Michas. “The dynamics involved are complex”, he says. “ For instance, fluid injection can cause earthquakes very far from where the injection took place and a very long time after it. It can take days, months or even years. ”

Elucidating the physical mechanisms involved with injecting fluids into a heterogenous ground

To understand exactly what is happening beneath our feet after fluids are injected into the ground, Dr. Georgios Michas intends to elucidate the precise physical processes involved with the diffusion of pore pressure – the pressure exerted by fluids on underground formations –, in the highly heterogeneous crust. To achieve his aim, Dr. Michas will conduct laboratory experiments subjecting rock samples to hydraulic fracturing. He will then monitor the propagation of pore pressure inside the sample by recording the acoustic emissions produced, and look at how the rock fractures in the presence of pressurized fluids. The next step will be to compare the observations obtained with real cases of fluid-induced earthquakes for which data is available. Finally, he will compile his results into a model of how pore-pressure propagates in time and space.

Since 2009, there has been a dramatic increase in earthquakes in the Central United States. This preoccupying phenomenon has been imputed to the injection of waste water from oil and gas operations into deep disposal wells by the United States Geological Survey (USGS). “The situation is pushing the government to change the legislation on oil extraction ”, reports Dr. Michas. “This is an example of why we need to be able to know where fluid injections can safely be made, and where they absolutely can’t ”. Even if man-made earthquakes don’t usually measure more than 4 to 5 on the Richter scale, a couple of them have reached a magnitude of 6 and even 7. The deadly Koynanagar quake of 1967 in India, which occurred after the reservoir behind a dam was filled up, measured 6.5 for instance. Dr. Georgios Michas’s research aims to provide a modeling tool capable predicting how fluids behave in the Earth’s crust. The ultimate goal is to prevent the potentially devastating consequences that could result from man-made earthquakes.

Understanding fluid-induced seismicity to mitigate the risks of man-made earthquakes

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