Stress in the Earth

Stress Stress is a force that changes a rocks shape or volume Because stress is a force it adds energy to the rock

Stress There are three types of stress occurring in the Earth’s crust: Shearing Tension Compression

Shearing When rock is pushed in opposite directions and the layers slide by each other.

Tension When rock layers pull apart and stretch.

Compression Caused when parts of the crust squeeze together.

Any change in the volume or shape of the layers is called deformation Slow deformation of the crust causes uplift and folding (mountain ranges). Rapid deformation of the crust results from Earthquakes

Faults If stress builds in a rock it can break. A fault is a break in the Earth’s crust where the rock moves.

Faults There are three basic types of faults: Strike-Slip (lateral) Normal Reverse

Strike-Slip Fault Caused by shearing forces Rocks on either side slide past each other.

Normal Fault Caused by tension The foot wall moves up relative to the hanging wall

Normal faults usually form at an angle The block that is above the crack is called the Hanging Wall The block that is below the crack is called the Foot Wall

Reverse Fault Caused by compression forces The foot wall moves down relative to the hanging wall

Reverse Fault A special type of reverse fault is a thrust fault In a thrust fault the hanging wall is pushed out over the foot wall