In geotechnical engineering, the behavior of soils under different loading conditions is pivotal for the design and analysis of civil engineering structures. Considering the dynamic interaction between soil and structures, particularly in seismic$-$prone regions, becomes paramount for ensuring structural integrity and safety. Discuss the fundamental principles governing soil$-$structure interaction in seismic zones, exploring factors such as soil liquefaction, site amplification effects, and the dynamic response of both shallow and deep foundations. Additionally, delve into the various methods employed for seismic analysis and design, including equivalent static analysis, response spectrum analysis, and time history analysis. Assess the effectiveness and limitations of each method in accurately predicting the response of structures subjected to seismic forces. Moreover, evaluate the significance of soil$-$structure interaction in the context of retrofitting existing structures for improved seismic resilience.