  The Newtonian solid-mechanical theory of nodeless spheroidal and torsional of
elastic seismic vibrations trapped in the crust of a quaking neutron star is
outlined and applied to the modal classification of the quasi-periodic
oscillations (QPOs) of X-ray luminosity in the aftermath of giant flares in SGR
1806-20 and SGR 1900+14. The presented analysis relies heavily on the
Samuelsson-Andersson identification of the QPOs frequency from the range 30-200
Hz with those for torsional nodeless vibrations of multipole degree in the
interval 2-12. Based on this identification, which is used to fix the input
parameters entering the obtained spectral formulae, we compute frequency
spectrum of nodeless spheroidal elastic vibrations. Particular attention is
given to the low-frequency QPOs in the data for SGR 1806-20 whose physical
origin has been called into question. Our calculations suggest that these
unspecified QPOs are due to nodeless dipole torsional (18 Hz) and dipole
spheroidal (26 Hz) elastic shear vibrations.
