Chapter 2

CHAPTER 2Earthquakes

EARTHQUAKES OCCUR ALONG FAULTSChapter 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

EARTHQUAKES RELEASE ENERGYChapter 2.2

ENERGY FROM EARTHQUAKES TRAVELS THROUGH EARTHSeismic Waves: energy waves that travel

as vibrations caused by earthquakesFocus: point underground where rocks

first begin to move, start of earthquakeEpicenter: point on Earth’s surface directly

above the focusEarthquakes are usually named for the city

closest to the epicenter

ENERGY FROM EARTHQUAKES TRAVELS THROUGH EARTH

WAVES AND ENERGY

What are some examples of waves in your world?

All waves including seismic waves carry energy from place to place

PRIMARY WAVESFastest seismic wavesAlso known as P-wavesTravel at 3mi/secParticles are pulled apart and pushed

together in the direction the waves’ travel

SECONDARY WAVESSecond seismic waves to arrive at a

location after an earthquakeAlso 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

SEISMIC WAVES

SEISMIC WAVES CAN BE MEASUREDSeismograph: instrument that constantly

records ground movements.

USING SEISMOGRAPHSRecord side-to-side and up-and-down

movements.Seismographs measure thousands of

earthquakes around the world every yearBy studying seismogram, scientists can

determine the locations and strengths of earthquakes.

LOCATING AN EARTHQUAKE1. 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

LOCATING AN EARTHQUAKE

Scientists use seismograph data to locate the focus of an earthquake

A seismogram can help determine an earthquakes magnitude (strength)

EARTHQUAKE DAMAGE CAN BE REDUCEDChapter 2.3

EARTHQUAKES CAN CAUSE SEVERE DAMAGE AND LOSS OF LIFEEvery 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.

EARTHQUAKE MAGNITUDE

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 DAMAGEBest to be outdoors far from buildings

during an earthquakeUse base isolators to insulate building

from shockShear walls add strength to a buildingCross braces add structure

STRUCTURES CAN BE DESIGNED TO RESIST EARTHQUAKE DAMAGE