  Sunquakes are created by the hydrodynamic response of the lower atmosphere to
a sudden deposition of energy and momentum. In this study we investigate a
sunquake that occurred in NOAA active region 11675 on 17 February 2013.
Observations of the corona, chromosphere and photosphere are brought together
for the first time with a non-linear force-free model of the active region's
magnetic field in order to probe the magnetic environment in which the sunquake
was initiated. We find that the sunquake was associated with the
destabilization of a flux rope and an associated M-class GOES flare. Active
region 11675 was in its emergence phase at the time of the sunquake and
photospheric motions caused by the emergence heavily modified the flux rope and
its associated quasi-separatrix layers, eventually triggering the flux rope's
instability. The flux rope was surrounded by an extended envelope of field
lines rooted in a small area at the approximate position of the sunquake. We
argue that the configuration of the envelope, by interacting with the expanding
flux rope, created a "magnetic lens" that may have focussed energy in one
particular location the photosphere, creating the necessary conditions for the
initiation of the sunquake.

Solar and Stellar Astrophysics