Layered crustal structures modulate the static co‑seismic displacement field. This study uses numerical simulation to investigate how elastic layered media, including high‑velocity layers (HVL) and low‑velocity layers (LVL), affect static co‑seismic displacement fields, with application to the 1976 Tangshan earthquake. Based on elastostatic dislocation theory and the PSGRN/PSCMP package, we compute surface displacement for strike‑slip and normal dislocations in stratified crustal models with HVLs/LVL of varying depth and thickness, excluding dynamic wave‑propagation effects. Shear‑modulus contrasts between layers produce opposite modulation by HVLs and LVLs. LVLs amplify static displacement amplitude and horizontal displacement; amplification grows with layer thickness but weakens at greater depth. For vertical displacement, LVLs weaken values near subsidence‑uplift junctions and amplify elsewhere. HVLs exert largely opposite effects: they generally reduce amplitude and horizontal displacement, showing near‑field amplification and far‑field weakening as thickness increases, while their influence fades with deeper burial. Application to the Tangshan strike‑slip earthquake confirms these patterns: real crustal LVL amplifies horizontal displacement and matches predicted vertical‑displacement behavior, though discrepancies against homogeneous‑half‑space results remain modest. A homogeneous half‑space model is reasonable for rapid preliminary seismic‑hazard evaluation, whereas high‑precision work requires realistic layered crustal structures. All layers are positioned above the fault plane; scenarios where faults cut HVLs/LVLs are reserved for future work.