C HAPTER 2 Earthquakes. E ARTHQUAKES O CCUR A LONG F AULTS Chapter 2.1.
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Transcript of C HAPTER 2 Earthquakes. E ARTHQUAKES O CCUR A LONG F AULTS Chapter 2.1.
ROCKS MOVE ALONG FAULTS
Fault: fracture or break in Earth’s lithosphere along which blocks of rock move past each other.
Stress: Force exerted when an object pushes or pulls on another object.
Earthquake: shaking of the ground caused by the sudden movement of large blocks of rock along a fault
ROCKS MOVE ALONG FAULTS
Most faults are located at tectonic plate boundaries 80% of all earthquakes occur in the belt around the
pacific ocean. San Andreas fault is best known fault in U.S.
FAULTS ARE CLASSIFIED BY HOW ROCKS MOVE
Normal Faults: occur as rocks are pulled apart common in the Great Rift Valley of Africa
REVERSE FAULTS
Occur near collision-zone boundaries Block of rock above the fault plane moves up relative to
the other block.
SLIP STRIKE FAULT
Blocks of rock move sideways on either side of the fault plane
Horizontal movement of rock
ENERGY FROM EARTHQUAKES TRAVELS THROUGH EARTH
Seismic Waves: energy waves that travel as vibrations caused by earthquakes
Focus: point underground where rocks first begin to move, start of earthquake
Epicenter: point on Earth’s surface directly above the focus
Earthquakes are usually named for the city closest to the epicenter
WAVES AND ENERGY
What are some examples of waves in your world?
All waves including seismic waves carry energy from place to place
PRIMARY WAVES
Fastest seismic wavesAlso known as P-wavesTravel at 3mi/secParticles are pulled apart and pushed
together in the direction the waves’ travel
SECONDARY WAVES
Second seismic waves to arrive at a location after an earthquake
Also known as S-wavesHalf the speed of primary wavesParticles of materials move at right angle
to the direction of the wave’s travel
SURFACE WAVES
Seismic waves that move along Earth’s surface
Slowest seismic waveCause the most damage
SEISMIC WAVES
USING SEISMOGRAPHS
Record side-to-side and up-and-down movements.
Seismographs measure thousands of earthquakes around the world every year
By studying seismogram, scientists can determine the locations and strengths of earthquakes.
LOCATING AN EARTHQUAKE
1. Scientists find the difference between the arrival times of the p and s waves at each of three stations
2. The time difference is used to determine the distance of the epicenter from each station
3. A circle is drawn around each station with a radius corresponding to the epicenter’s distance from that station
LOCATING AN EARTHQUAKE
Scientists use seismograph data to locate the focus of an earthquake
A seismogram can help determine an earthquakes magnitude (strength)
EARTHQUAKES CAN CAUSE SEVERE DAMAGE AND LOSS OF LIFE
Every year on average an earthquake of magnitude 8 or higher strikes somewhere on Earth.
Most injuries and deaths are not caused by the movement of the ground but by collapsing buildings and fires.
EARTHQUAKE MAGNITUDE
First scale developed by Charles Richter, the Richter scale.
Newer scale is called the moment magnitude scale Each step up is an increase of 32 times the previous
value.
DAMAGE FROM EARTHQUAKES
Aftershock: smaller earthquake that follows a more powerful earthquake in the same area.
Liquefaction: a process in which shaking of the ground causes soil to act like a liquid.
Tsunami: water wave triggered by an earthquake, volcanic eruption or landslide.
2004 Sumatra tsunami killed nearly 300,000 people
SCIENTISTS WORK TO MONITOR AND PREDICT EARTHQUAKES
STRUCTURES CAN BE DESIGNED TO RESIST EARTHQUAKE DAMAGE
Best to be outdoors far from buildings during an earthquake
Use base isolators to insulate building from shock
Shear walls add strength to a buildingCross braces add structure