  We present the results of a radio multi-frequency ($\rm 3-340~GHz$) study of
the blazar 3C~454.3. After subtracting the quiescent spectrum corresponding to
optically thin emission, we found two individual synchrotron self-absorption
(SSA) features in the wide-band spectrum. The one SSA had a relatively low
turnover frequency ($\nu_{\rm m}$) in the range of $\rm 3-37~GHz$ (lower
$\nu_{\rm m}$ SSA spectrum, LSS), and the other one had a relatively high
$\nu_{\rm m}$ of $\rm 55-124~GHz$ (higher $\nu_{\rm m}$ SSA spectrum, HSS).
Using the SSA parameters, we estimated magnetic field strengths at the surface
where optical depth $\tau=1$. The estimated magnetic field strengths were $\rm
>7~mG$ and $\rm >0.2~mG$ for the LSS and HSS, respectively. The LSS emitting
region was magnetically dominated before the June 2014 $\gamma$-ray flare. The
quasi-stationary component (C), $\sim 0.6~{\rm mas}$ apart from the 43 GHz
radio core, became brighter than the core with decreasing observing frequency,
and we found that component C was related to the LSS. A decrease in jet width
was found near component C. As a moving component, K14 approached component C,
and the flux density of the component was enhanced while the angular size
decreased. The high intrinsic brightness temperature in the fluid frame was
obtained as $T_{\rm B, int} \approx (7.0\pm1.0) \times 10^{11}~{\rm K}$ from
the jet component after the 2015 August $\gamma$-ray flare, suggesting that
component C is a high-energy emitting region. The observed local minimum of jet
width and re-brightening behavior suggest a possible recollimation shock in
component C.
