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.