  We model rapid variability of multifrequency emission from blazars occurring
across the electromagnetic spectrum (from radio to gamma-rays). Lower energy
emission is produced by the synchrotron mechanism, whereas higher energy
emission is due to inverse Compton scattering of the synchrotron emission. We
take into account energy stratification established by particle acceleration at
shock fronts and energy losses due to synchrotron emission. We also consider
the effect of light travel delays for the synchrotron emission that supplies
the seed photons for inverse Compton scattering. The production of a flare is
caused by the collision between a relativistic shock wave and a stationary
feature in the jet (e.g., a Mach disk). The collision leads to the formation of
forward and reverse shocks, which confine two contiguous emission regions
resulting in complex profiles of simulated flares. Simulations of
multifrequency flares indicate that relative delays between the inverse Compton
flares and their synchrotron counterparts are dominated by energy
stratification and geometry of the emitting regions, resulting in both negative
and positive time delays depending on the frequency of observation. Light
travel effects of the seed photons may lead to a noticeable delay of the
inverse Compton emission with respect to synchrotron variability if the line of
sight is almost perfectly aligned with the jet. We apply the model to a flare
in 3C 273 and derive the properties of shocked plasma responsible for the
flare. We show that the pronounced negative time delay between the X-ray and IR
light curves (X-rays peak after the maximum in the synchrotron emission) can be
accounted for if both forward and reverse shocks are considered.
