Here's why:

* Ductile deformation occurs when rocks bend and flow under pressure, similar to how modeling clay behaves. It happens when the pressure is applied slowly over a long period of time, and the rocks are relatively warm and under high confining pressure.

* Brittle deformation, on the other hand, is what leads to earthquakes. This happens when rocks break suddenly under stress, releasing energy in the form of seismic waves.

Key characteristics of ductile deformation:

* Folding: Rocks bend into waves or folds without breaking.

* Stretching and thinning: Rocks become elongated and thinner under stress.

* Flow: In extreme cases, rocks can even flow like a viscous fluid over long timescales.

Examples of ductile deformation:

* The formation of mountains through folding and faulting.

* The stretching and thinning of the Earth's crust in rift valleys.

* The flow of rocks deep within the Earth's mantle.

Ductile deformation is important for understanding the following:

* Plate tectonics: It plays a key role in the movement and interaction of tectonic plates.

* Mountain building: It shapes the Earth's surface and creates many of the world's mountain ranges.

* Geological history: Studying deformed rocks helps us understand past geological events and processes.

So, while brittle deformation leads to earthquakes, ductile deformation is a slow, gradual process that shapes the Earth's landscape over millions of years.