  We study the core shift effect in the parsec scale jet of the blazar 3C 454.3
using the 4.8 GHz - 36.8 GHz radio light curves obtained from three decades of
continuous monitoring. From a piecewise Gaussian fit to each flare, time lags
$\Delta t$ between the observation frequencies $\nu$ and spectral indices
$\alpha$ based on peak amplitudes $A$ are determined. From the fit $\Delta t
\propto \nu^{1/k_r}$, $k_r = 1.10 \pm 0.18$ indicating equipartition between
the magnetic field energy density and the particle energy density. From the fit
$A \propto \nu^\alpha$, $\alpha$ is in the range $-0.24$ to $1.52$. A mean
magnetic field strength at 1 pc, $B_1 = 0.5 \pm 0.2$ G, and at the core,
$B_{\rm core} = 46 \pm 16$ mG, are inferred, consistent with previous
estimates. The measure of core position offset is $\Omega_{r\nu} = 6.4 \pm 2.8$
pc GHz$^{1/k_r}$ when averaged over all frequency pairs. Based on the
statistical trend shown by the measured core radius $r_{\rm core}$ as a
function of $\nu$, we infer that the synchrotron opacity model may not be valid
for all cases. A Fourier periodogram analysis yields power law slopes in the
range $-1.6$ to $-3.5$ describing the power spectral density shape and gives
bend timescales in the range $0.52 - 0.66~$yr. This result, and both positive
and negative $\alpha$, indicate that the flares originate from multiple shocks
in a small region. Important objectives met in our study include: the
demonstration of the computational efficiency and statistical basis of the
piecewise Gaussian fit; consistency with previously reported results; evidence
for the core shift dependence on observation frequency and its utility in jet
diagnostics in the region close to the resolving limit of very long baseline
interferometry observations.
