Here's why:

* Earthquakes and Soil Liquefaction: Earthquakes can cause soil liquefaction, where the ground essentially turns to liquid mud. This happens when the shaking causes the water in the soil to rise and displace the solid particles.

* Uneven Settlement: When the ground beneath a building settles unevenly, the foundation can sink or shift at different rates.

* Structural Damage: This uneven settlement can lead to cracks in walls, floors, and ceilings, as well as misalignment of doors and windows. In severe cases, it can even cause the building to collapse.

In summary: Uneven settlement after an earthquake is a sign that the earthquake has affected the soil beneath the building, leading to foundation instability.