Earthquakes

8th Grade Science

Earthquakes - What are they?

-Vibrations in the ground- result from movement along breaks in Earth’s lithosphere.

-Faults – breaks in rock.

-Occur mostly at plate boundaries.

Types of Faults

1. Strike-Slip

2. Normal

3. Reverse

Strike-Slip: fault blocks slide horizontally in opposite directions.

-seen at transform boundaries.

Normal: fault blocks are pulled apart.-seen at divergent boundaries.

Reverse: fault blocks are pushed together.-seen at convergent

boundaries.

Seismic Waves-Earthquake waves – vibrations on

and in Earth.

Focus vs. Epicenter

-Focus – location inside Earth where earthquake originates.

-Epicenter – location on Earth’s surface directly above focus.

Types of Seismic Waves-Primary (P) waves: push-pull motion.

-fastest

-1st to be detected

-travel through solids & liquids

Types of Seismic Waves-Secondary (S) waves: up & down motion.

-slower than P but faster than surface

-travel only through solids

Types of Seismic Waves-Surface waves: up & down + rolling motion.

-slowest

-cause most damage on Earth

• Scientists that study earthquakes are called seismologists.

• They use the properties of seismic waves to map Earth’s interior.

• An instrument called a seismometer measures and records ground motion and the distance and direction that seismic waves travel.

• Ground motion is recorded as a seismogram, a graphical illustration of earthquake waves

Earthquake Magnitude

-Richter Scale – most used.

-begins at zero, goes through 10

-each increase on scale is ten

times greater.

-Mercalli Scale – based on damage. Ranges from I

through XII.

Japan suffered its worst earthquake in a decade in October 2004, when a magnitude 6.6 quake rattled Niigata Prefecture, killing dozens and displacing 100,000 people. Scientists often can say where such extreme shaking is likely to hit—but still can't tell when

Split in two: A damaged apartment block in Concepcion, Chile. February 28, 2010-8.8 magnitude

On August 15, 2007, a Mw 8.0, earthquake occurred off the coast of Peru. According to the USGS, the earthquake killed over 500 people and injured more than 1,000, destroying more than 35,500 buildings and damaging 4,200 more. Widespread communications and power outages occurred. The Pan-American Highway and other transportation routes suffered heavy damage due to landslides and faulting that resulted from liquefaction of sandy and silty soils near the Pacific Ocean.