tokens: our best guess associates the sunquake location (taken to be the 5 mHz signal in Figure 1 ) to the connectivity domain indicated as Q 4 in Figure 12 . That connectivity domain corresponds to the domain 4 in Figure 13 , i.e., to the envelope bundle of field lines (in green in Figure 14 ). Given its structure, such a field line bundle has two interesting properties. First, since it is surrounding the flux rope in almost its entire length it is then directly impacted when the eruption occurs. Second, such wide-spread field lines between the erupting flux rope and the above layered structure are all connected on one side to a very small area in the photosphere (where the sunquake occurs), in this way, providing a sort of magnetic focusing. In light of this, we argue that the sunquake is a consequence of the energy release associated with the reconnection between the erupting flux rope and the envelope surrounding it. Furthermore, the envelope structure helps focus the released energy into a small area in the lower atmosphere ( Q 4 in Figure 12 ), which produces the sunquake pulse. The scenario offered by our analysis and the interpretation of the observations clarifies the dynamics of the two flares and supports the association of the sunquake to the larger, M-class flare, rather than to the first C-class flare. Moreover, it indicates how a sunquake may require a special magnetic field configuration to occur, which may help understand their erratic occurrence. 6. Conclusion In this work, we study the evolution of active region 11675 on 2013 February 17, in the hours leading to the production of two flares (a C-class flare and an M-class flare), the ejection of filament material and a sunquake. We investigate the configuration of the active region magnetic field through the construction of an NLFFF extrapolation just over one hour before the sunquake. The aim of the work is to shed light on the configuration of the coronal magnetic field in which the sunquake was produced. The sunquake occurs when active region 11675 is undergoing a period of rapid evolution during its emergence phase, and when there are strong motions of the photospheric magnetic field elements. In particular, two emerging bipoles collide and shear past each other. The magnetic field along the polarity inversion line that separates these bipoles is highly sheared and at low altitudes bald patch field lines are present. At higher altitudes, an HFT and a flux rope are present, which have been highly modified by the motions of the photospheric field in which these magnetic structures are rooted. From a time–distance analysis, we determine that the sunquake was initiated in the time period between 15:50:41 to 15:51:26 UT on 2013 February 17 in a region of positive polarity field. This finding indicates that the sunquake is initiated during the M-class flare, which is associated with the eruption of the flux rope and ejection of filament material. However, this timing determination
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