  We consider weakly coupled systems of semilinear viscoelastic wave equations
with different power source nonlinearities in $\mathbb{R}^n$, $n\geq1$ as
follows: \begin{equation*} \left\{\begin{aligned} &u_{tt}-\Delta u+g\ast\Delta
u+u_t=|\partial_t^{\ell}v|^p,\\ &v_{tt}-\Delta v+g\ast\Delta
v+v_t=|\partial_t^{\ell}u|^q,\\ \end{aligned}\right. \end{equation*} with
$\ell=0,1$ and $p,q>1$. After presenting $L^m-L^r$ estimates with $1\leq m\leq
r\leq \infty$ of solutions to the corresponding linearized problem with
vanishing right-hand side, we prove the existence of global in time solutions
to the weakly coupled systems, where the initial data are supposed to belong to
different $L^r$ spaces with different additional $L^m$ regularities.
