What structures are most vulnerable to earthquakes?

Structures most vulnerable to earthquakes include unreinforced masonry buildings, poorly designed or constructed high-rise buildings, and older infrastructures that don't comply with modern seismic codes. These structures often lack the flexibility and strength needed to withstand seismic forces, leading to increased risk of collapse. Additionally, buildings on soft soil or near fault lines face greater risks due to ground shaking and potential liquefaction. Proper engineering and retrofitting can mitigate these vulnerabilities.