Earthquake engineering is essential for designing structures that can withstand seismic forces and minimize damage during earthquakes. Elaborate on the theoretical principles of seismic hazard analysis, including probabilistic seismic hazard assessment $($PSHA$)$ and ground motion modeling. Discuss theoretical approaches to seismic design criteria, such as performance$-$based design and seismic retrofitting strategies, and analyze their efficacy in enhancing structural resilience and reducing seismic risk.