  Magnetar giant flares may excite vibrational modes of neutron stars. Here we
compute an estimate of initial post-flare amplitudes of both the torsional
modes in the magnetar's crust and of the global f-modes. We show that while the
torsional crustal modes can be strongly excited, only a small fraction of the
flare's energy is converted directly into the lowest-order f-modes. For a
conventional model of a magnetar, with the external magnetic field of about
10^{15} Gauss, the gravitational-wave detection of these f-modes with advanced
LIGO is unlikely.
