[S02-4] Studies of seismicity at Koyna, India and other holistic approach projects

[S02-4-05] Mapping microseismicity induced by hydrofrac experiments in Europe

^○Torsten Dahm, Simone Cesca, Jose Angel Lopez Comino, Sebastian Heimann, Claus Milkereit, Arno Zang (GFZ German Research Centre for Geosciences, Potsdam, Germany)

Hydraulic fracturing can be performed to increase the rock permeability and enhance the exploitation of shale gas and has been increasingly applied in recent years on a global level, but remains poorly developed in Europe, partially because of the disputed environmental consequences. Here, we only consider the seismic hazard associated to hydraulic fracturing, and focus the problem from a seismological viewpoint. Although moderate magnitude events have been attributed to hydrofrac operations, the seismic response to fracturing is expected as local microseismicity. This poses important challenges to the detection and localization of weak events, identification of fracture migration and the spatial mapping of fracture distribution and permeability. At the same time, large data volumes currently recorded by dense microseismic networks provide unprecedented information on microseismicity. New tools need to be automatized so that large datasets can be handled and the data mined. Furthermore, a seismic detector needs to be quick, so that massive datasets can be processes in a reasonable time, whereas a seismic locator needs to be accurate, so that the small-scale patterns and migration of rupture processes can be resolved. We adopt here recently developed tools, designed to detect coincident arrivals of seismic energy at seismic stations in a local network and locate their source. We discuss two applications to hydraulic fracturing in Europe. The first is a small-scale experiment in a Swedish mine, where thousands of microfractures (acoustic emissions) are detected and located during an hydraulic fracturing experiment. The second concerns a recently exploited hydraulic fracturing site in Poland, monitored in the framework of the EU project SHEER. There, we analyse realistic synthetic data and real data to discuss one of the first cases in Europe, where an independent seismic monitoring of hydraulic fracturing operations was performed.