  Sunquakes are enhanced seismic waves excited in some energetic solar flares.
Up to now, their origin has still been controversial. In this Letter, we select
and study 20 strong flares in Solar Cycle 24, whose impulse phase is fully
captured by the \emph{Reuven Ramaty High Energy Solar Spectroscopic Imager}
(\emph{RHESSI}). For 11 out of 12 sunquake-active flares in our sample, the
hard X-ray (HXR) emission shows a good temporal and spatial correlation with
the white-light (WL) enhancement and the sunquake. Spectral analysis also
reveals a harder photon spectrum that extends to several hundred keV, implying
a considerable population of flare-accelerated nonthermal electrons at high
energies. Quantitatively, the total energy of electrons above 300 keV in
sunquake-active flares is systematically different from that in sunquake-quiet
flares, while the difference is marginal for electrons above 50 keV. All these
facts support highly energetic electrons as a preferred driver of the
sunquakes. Such an electron-driven scenario can be reasonably accommodated in
the framework of a recently proposed selection rule for sunquake generation.
For the remaining one event, the sunquake epicenter is cospatial with a
magnetic imprint, i.e., a permanent change of magnetic field on the
photosphere. Quantitative calculation shows that the flare-induced downward
Lorentz force can do enough work to power the sunquake, acting as a viable
sunquake driver for this specific event.
