Earthquakes

Earthquakes

8th Grade Science

Earthquakes

Vibrations in the ground that result from movement along faults or breaks in Earth's Lithosphere.

Types of Faults

• Normal Faults

• Strike-Slip Faults

• Reverse Faults

Normal Fault

form when forces pull rocks apart along a divergent plate boundary, block of rock above the fault moves down.

Strike-Slip Fault

Two blocks of rock slide horizontally past each other in opposite directions.

Reverse Fault

Force pushes two blocks of rock together with the rock above the fault moving up.

Focus and Epicenter

Focus - point beneath the Earth's surface where rock under stress breaks to cause an earthquake.

Epicenter - point on the surface directly above the focus.

Seismic Waves

Waves that carry energy of an earthquake away from the focus, there are three types:

Primary Waves

Secondary Waves

Surface Waves

Types of Waves

• Primary Waves (P Waves) - compression waves that travel through solids and liquids, compressing and expanding the material they pass through, temporarily changing volume.

• Secondary Waves (S Waves) - only travel through solids and temporarily change the shape, but not the volume of the material they pass through, move slower than P Waves.

• Surface Waves - move slower than P and S waves, but can produce severe ground movement with a wavelike motion.

Locating an Earthquake

Locating an earthquake's epicenter is done using triangulated data from at least three different seisometers, or devices that measure and record ground motion and helps determine the distance seismic waves travel.

Steps for Locating Earthquakes

• Find the arrival time difference between the first P-wave and S-wave which is called lag time.

• Find the distance to the epicenter by using a graph of lag time vs. distance, then go from y-axis to line and read down to x-axis.

• Locate the epicenter by using a map scale to mark radius on a compass then draw a circle around each seismometer location to find intersecting point.

Multiple Choice

where quake begins below surface

• elastic rebounding

• focus

• epicenter

• fault

Multiple Choice

back and forth motion

• S-wave

• P-wave

• elastic rebounding

• L-wave

Multiple Choice

new normal

• joint

• seismic waves

• elastic rebounding

• epicenter

Multiple Choice

crack with movement

• focus

• joint

• fault

• epicenter

Multiple Choice

What type of stress forms a plateau?

• tension
• compression
• shearing
• reverse

Multiple Choice

What type of fault is shown in this picture?

• normal
• reverse
• strike slip
• tension

Multiple Choice

Which type of seismic waves cause the most damage?

• P waves
• S waves
• surface waves
• tsunami waves

Multiple Choice

At what plate boundary will a strike slip fault be found?

• divergent
• transform
• convergent
• all of them

Multiple Choice

Tension causes what type of fault to form?

• folds
• reverse fault
• strike slip fault
• normal fault

Multiple Choice

The best way to protect yourself in an earthquake is to 

• run as fast as you can
• drop, cover and hold
• stop, drop and roll
• go into the basement