  We study holographic subregion volume complexity for a line segment in the
AdS$_3$ Vaidya geometry. On the field theory side, this gravity background
corresponds to a sudden quench which leads to the thermalization of the
strongly-coupled dual conformal field theory. We find the time-dependent
extremal volume surface by numerically solving a partial differential equation
with boundary condition given by the Hubeny-Rangamani-Takayanagi surface, and
we use this solution to compute holographic subregion complexity as a function
of time. Approximate analytical expressions valid at early and at late times
are derived.
