Rupture Directivity in 3D Inferred From Acoustic Emissions Events in a Mine-Scale Hydraulic Fracturing Experiment López Comino, José Ángel Cesca, Simone Niemz, Peter Dahm, Torsten Zang, Arno Directivity Earthquake source Induced seismicity Hydraulic fracturing Acoustic emissions This research has been funded by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement N degrees 754446 and UGR Research and Knowledge Transfer Found -Athenea3i; and by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) -Projektnummer (407141557). SC and PN received funding from the EU project PostMinQuake, RFCS (899192). AZ was supported by funding received from the European Union's Horizon 2020 research and innovation programme, Grant Agreement No. 691728 (Destress). The in situ experiment at Äspö Hard Rock Laboratory (HRL) was supported by the GFZ German Research Center for Geosciences (75%), the KIT Karlsruhe Institute of Technology (15%) and the Nova Center for University Studies, Research and Development Oskarshamn (10%). An additional in-kind contribution of the Swedish Nuclear Fuel and Waste Management Co. (SKB) for using Äspö HRL as test site for geothermal research is greatly acknowledged. Rupture directivity, implying a predominant earthquake rupture propagation direction, is typically inferred upon the identification of 2D azimuthal patterns of seismic observations for weak to large earthquakes using surface-monitoring networks. However, the recent increase of 3D monitoring networks deployed in the shallow subsurface and underground laboratories toward the monitoring of microseismicity allows to extend the directivity analysis to 3D modeling, beyond the usual range of magnitudes. The high-quality full waveforms recorded for the largest, decimeter-scale acoustic emission (AE) events during a meter-scale hydraulic fracturing experiment in granites at similar to 410 m depth allow us to resolve the apparent durations observed at each AE sensor to analyze 3D-directivity effects. Unilateral and (asymmetric) bilateral ruptures are then characterized by the introduction of a parameter kappa, representing the angle between the directivity vector and the station vector. While the cloud of AE activity indicates the planes of the hydrofractures, the resolved directivity vectors show off-plane orientations, indicating that rupture planes of microfractures on a scale of centimeters have different geometries. Our results reveal a general alignment of the rupture directivity with the orientation of the minimum horizontal stress, implying that not only the slip direction but also the fracture growth produced by the fluid injections is controlled by the local stress conditions. 2021-06-15T12:22:21Z 2021-06-15T12:22:21Z 2021-05-17 info:eu-repo/semantics/article López-Comino JÁ, Cesca S, Niemz P, Dahm T and Zang A (2021) Rupture Directivity in 3D Inferred From Acoustic Emissions Events in a Mine-Scale Hydraulic Fracturing Experiment. Front. Earth Sci. 9:670757. doi: [10.3389/feart.2021.670757] http://hdl.handle.net/10481/69193 10.3389/feart.2021.670757 eng info:eu-repo/grantAgreement/EC/H2020/754446 info:eu-repo/grantAgreement/EC/H2020/691728 http://creativecommons.org/licenses/by/3.0/es/ info:eu-repo/semantics/openAccess Atribución 3.0 España Frontiers Research Foundation