  We studied the pc-scale core shift effect using radio light curves for three
blazars, S5 0716+714, 3C 279 and BL Lacertae, which were monitored at five
frequencies ($\nu$) between 4.8 GHz and 36.8 GHz using the University of
Michigan Radio Astronomical Observatory (UMRAO), the Crimean Astrophysical
Observatory (CrAO), and Metsahovi Radio Observatory for over 40 years. Flares
were Gaussian fitted to derive time delays between observed frequencies for
each flare ($\Delta t$), peak amplitude ($A$), and their half width. Using $A
\propto \nu^{\alpha}$ we infer $\alpha$ in the range $-$16.67 to 2.41 and using
$\Delta t \propto \nu^{1/k_r}$, we infer $k_r \sim 1$, employed in the context
of equipartition between magnetic and kinetic energy density for parameter
estimation. From the estimated core position offset ($\Omega_{r \nu}$) and the
core radius ($r_{\rm core}$), we infer that opacity model may not be valid in
all cases. The mean magnetic field strength at 1 pc ($B_1$) and at the core
($B_{\rm core}$), are in agreement with previous estimates. We apply the
magnetically arrested disk model to estimate black hole spins in the range
$0.15-0.9$ for these blazars, indicating that the model is consistent with
expected accretion mode in such sources. The power law shaped power spectral
density has slopes $-$1.3 to $-$2.3 and is interpreted in terms of multiple
shocks or magnetic instabilities.
