  We consider the possibilities for obtaining information about the equation of
state for quark matter by using future direct observational data on
gravitational waves. We study the nonradial oscillations of both fluid and
spacetime modes of pure quark stars. If we observe the $f$ and the lowest
$w_{\rm II}$ modes from quark stars, by using the simultaneously obtained
radiation radius we can constrain the bag constant $B$ with reasonable
accuracy, independently of the $s$ quark mass.
