Chapter 2 Lesson 1

Earthquakes occur along faults

Rocks Move Along Faults

• Fault – a fracture, or break, in Earth’s lithosphere, along which blocks of rock move past each other

• As rocks in the faults bend, a lot of stress is put on them

• Stress – force exerted when an object presses on, pulls on, or pushes against another object

Rocks Move Along Faults

• The sudden release of stress causes an

earthquake: shaking of the ground caused by sudden movement of large blocks of rock along a fault

• Most faults are located along tectonic plate boundaries

• The strength of an earthquake depends on:• How much stress builds

up before the rocks move

• The distance the rocks move

80 percent of all earth-quakes occur in a belt around the edges of the Pa-cific Ocean [Pacific Rim]

Rocks Move Along Faults

• ALL earthquakes occur in the lithosphere [it is dense, solid]

• FEW earthquakes occur below the lithosphere only because the tec-tonic plates are still cold to break

Faults are classified by how rocks move

•3 main types of faults•Normal faults – pulled apart

•Reverse faults – pushed/pressed together

•Strike-slip faults – move sideways

Normal Faults

• Stress pulls rocks apart

• Common near bound-aries where tectonic plates are moving apart

• Ex. Great Rift Valley of Africa

Reverse Faults

• Block of rock above the fault plane moves up relative to the other block

• Stress presses rocks to-gether

• Faults can occur near collision-zone bound-aries

• Ex. Continental/Oceanic collision

Strike-Slip Faults

• Rock move sideways on either side of the fault plane

• Stress pushes rocks hor-izontally

• Occurs near plates that scrape past each other

• Ex. San Andreas Fault