According to scientists from École Polytechnique Fédérale de Lausanne EPFL and the Ecole Normale Supérieure in Paris, pressurized ground water can reduce the intensity of seismic events.
Underground human activity like mining, geothermal energy production, gas and oil extraction, toxic waste or CO2 storage, and the construction of tunnels and dam reservoirs can sometimes trigger earthquakes, a phenomenon referred as induced seismicity. Especially in Switzerland, 2 seismic incidents, one near Basel and the other in St. Gallen with a Mw 3.4 and a Mw 3.5 in 2006 and 2013, respectively, were recorded due to geothermal projects. These earthquakes are not as hazardous as natural induced events but the fact that they are caused by human activity is disadvantageous for these kind of projects. Acosta, a PhD student at LEMR (Laboratory of Experimental Rock Mechanics) of EPFL and the study's lead author states: "These earthquakes may be low in intensity, but they can cause damage and affect public opinion – to the point of derailing projects."
Researchers studied the role of fluids in the propagation of induced earthquakes in order to evaluate the underlying mechanisms. They discovered that highly pressurized water tends to limit the intensity of an earthquake, a finding that is considered revolutionary with respect to the present perceptions.
Acosta investigated the impact of underground water of fault dynamics by conducting tests replicating earthquake's conditions. He mostly focused on seismic events caused by two plates in a fault rubbing against each other, producing seismic waves that propagate to the surrounding area. According to Acosta's results "Rock friction generates a significant amount of heat, which further fuels the propagation effect. Some of this heat is absorbed by the water in the surrounding rock, and the amount absorbed depends to a large extent on the water's thermodynamic parameters. What we learned from our experiments is that the closer the fluid's initial pressure is to the critical pressure of water, the weaker the earthquake will be." Study's 2nd author, François-Xavier Passelègue, a LEMR researcher, points out that the initial fluid pressure in the rocks is crucial especially at depths commonly reached by geothermal activities. He also emphasizes on the significance of considering this finding in geothermal models.
Researchers recently acquired state-of-the-art equipment and now have the capability of simulating the pressure and temperature a depths of 10-15 km in order to further study the influence of groundwater pressure on earthquake magnitude.
Source: Actu.epfl.ch
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