On the system of $2$-D elastic waves with critical space dependent damping

Abstract

We consider the system of elastic waves with critical space dependent damping $V(x)$. We study the Cauchy problem for this model in the $2$-dimensional Euclidean space ${\mathbf{R}}^2$, and we obtain faster decay rates of the total energy as time goes to infinity. In the $2$-D case we do not have any suitable Hardy type inequality, so generally one has no idea to establish optimal energy decay. We develope a special type of multiplier method combined with some estimates brought by the $2$-D Newton potential belonging to the usual Laplacian $-\Delta$, not the operator $-a^2\Delta -(b^2-a^2)\nabla \mathrm{div}$ itself. The property of finite speed propagation is important to get results for this system.

13 pages by 11 point. Corrected a typo in the absolute value in Lemma 2.6