FOCUS

Mrs. Neistadt Physical Science

As tectonic plates move, friction causes the rocks at plate boundaries to stretch or compress.

*Potential (stored) energy in rocks transformed to ground-shaking kinetic (movement) energy causes an earthquake.

* Earthquakes begin in the lithosphere at a point called the focus.

*Seismic waves reach Earth’s surface at a point above the focus called the epicenter.

*The release of potential energy to kinetic energy in rocks results in seismic waves.

These waves radiate from the focus traveling about 20 times faster than the speed of sound.

*Body Waves and Surface Waves: *Body Waves originate from the focus of an

earthquake *When body waves reach the epicenter, they

become surface waves. They move more slowly, and causes more damage.

Body Waves originate from the focus of an earthquake.

*P-waves (primary waves) are compression waves that push and pull rock as they move through it.

*S-waves (secondary waves) move sideways and up and down, traveling about 3 k/sec.◦ *S-waves do not travel through liquids.

*Earthquakes are measured by the magnitude or size of the energy of the seismic waves.

*There are several different scales to measure earthquakes. ◦ The *Richter Scale measure the amplitude of the seismic

waves recorded on a seismograph.◦ The *Moment Magnitude Scales rates the total energy

released by an earthquake.◦ The *Mercalli Scale rates how much damage was

caused to buildings, the ground and to people.

1. What is the difference between the focus and the epicenter of an earthquake?

2. Draw a diagram that shows the difference between a P-wave and an S-wave.

3. Describe the differences between P-waves and S-waves.

4. An earthquake in the eastern hemisphere of Earth is recorded in the western hemisphere. However, only P-waves are recorded. Review what you know about P and S waves and come up with an explanation for this data.

5. Define the work of a geologist, paleontologist, and seismologist, each in your OWN words. If you had to choose to be one of these scientists, which would you be and why?

Types of Faults

Faults are breaks in the Earth’s crust. Most faults occur along the boundaries of tectonic

plates. In the USA, the San Andreas Fault of California is

the most active fault.

The direction a block of rocks moves along different types of Faults depends on the kind of stresses they are under.

*Faults are classified according to the way the rocks on one side of the Fault move in relation to the rocks on the other side.

Faults Are Classified By How Rocks MoveFaults Are Classified By How Rocks Move

• *There are Three main types of Faults:– 1. Normal Faults– 2. Reverse Faults– 3. Strike-Slip Faults

• More than one type of Fault may be present along the same Plate Boundary.

• However the type of Fault that is most common along a boundary depends if the plates are pulling apart, pushing together, or scraping past one another at that boundary.

• *There are Three main types of Faults:– 1. Normal Faults– 2. Reverse Faults– 3. Strike-Slip Faults

• More than one type of Fault may be present along the same Plate Boundary.

• However the type of Fault that is most common along a boundary depends if the plates are pulling apart, pushing together, or scraping past one another at that boundary.

A Fault forms a flat plane that extends horizontally and vertically.

Blocks of rock move along the Fault Plane during an earthquake.

Faults Are Classified By How Rocks MoveFaults Are Classified By How Rocks Move

Fault Plane Normal FaultNormal Fault

*Along a Normal Fault, the block of rock above the Fault Plane slides down in relation to the other rock.

*Normal Faults are often found at Divergent Plate Boundaries.

Earthquakes along Normal Faults are common near boundaries where Tectonic Plates are moving apart, such as the in the Great Rift Valley of Africa.

*Along a Reverse Fault, the block of rock above the Fault Plane move up in relation to the other block.

Reverse Faults are often found at Convergent boundaries.

*Along a Strike-Slip Fault the blocks move sideways on either side of the Fault Plane.

Strike-Slip Faults are often found at transform plate boundaries.

*These Faults can occur where plates scrape past each other. The San Andreas is a Strike-Slip Fault.

Over time, movement of rocks along Normal and Reverse Faults can push up mountains and form deep Valleys.

As rock moves along Strike-Slip Faults, rocks that were once continuous layers can become separated by hundreds of kilometers.

1. Explain how divergent plate boundaries and normal faults are related.

2. Explain how convergent plate boundaries and reverse faults are related.

3. Explain how transform plate boundaries are related to strike slip faults.

4. What kind of fault is the San Andreas Fault?

1. Color the fault blocks, 2. Cut out, 3. Fold all straight lines and fit. 4. Glue: use a small amount of glue on tabs. Use a small piece of tape to hold glued surfaces together until glue dries.

Normal Fault Reverse Fault Strike-Slip Fault Fault Plane Horizontal Vertical Collision