How to estimate the maximum frequency my model could resolved properly?

Dear all,
Theoretically, the SEM used in SPECFEM3D require that the local element size should smaller than local minimum wavelength for a certain frequency. However, in the output_solver, the minimum period resolved is calculate by global_max_element_size /min(vs)*5/4. That is, very small velocity in the subsurface also require a small element size in deep part for the simulation of high frequency(might up to 5hz). I don’t know very well about SEM. Can someone help me solve my doubts? I’d be grateful!

Best wishes!