  The spectrally truncated, or finite dimensional, versions of several
equations of inviscid flows display transient solutions which match their
viscous counterparts, but which eventually lead to thermalized states in which
energy is in equipartition between all modes. Recent advances in the study of
the Burgers equation show that the thermalization process is triggered after
the formation of sharp localized structures within the flow called "tygers". We
show that the process of thermalization first takes place in well defined
subdomains, before engulfing the whole space. Using spatio-temporal analysis on
data from numerical simulations, we study propagation of tygers and find that
they move at a well defined mean speed that can be obtained from energy
conservation arguments.
