Earthquakes

10.1Forces Inside Earth

EARTHQUAKES

I. Causes of EarthquakesA. Passing the Elastic Limit Causes Faulting

a. Earth’s rocks will bend and stretch up to a point

b. After that point, rocks may break

c. Faults – area where rocks move when elastic limit is passed

d. Faults form along plate boundaries

e. Earthquakes – rock breaking that releases stored energy to produce vibrations

II. Types of FaultsA. Normal Faults

a. Tension forces pull rock apart.

b. Rock above fault surface moves downward in relation to the rock below the surface.

B. Reverse Faultsa. Compression forces push rocks together.

b. Rock above the fault surface are forced up over the rocks below the fault surface.

C. Strike-Slip Faultsa. Shear forces move rocks sideways past

each other.

b. Rocks on either side of the fault are moving past each other without much upward or downward movement.

c. As forces keep driving the plates to move, energy builds up and rocks reach their elastic limit.

d. When rocks are stressed past their elastic limit, they may break and an earthquake may result.

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10.2Earthquake Information

EARTHQUAKES

I. Types of Seismic WavesA. Seismic waves – energy waves made by

earthquakesB. Earthquake Focus

a. Focus – the point in Earth’s interior where the energy release occurs

b. Seismic waves are produced and travel outward

C. Seismic Wavesa. Primary waves – waves that cause particles in rocks to

move back and forth in the same direction as the wave

b. Squeeze together and stretch apart as waves move

c. Secondary Waves – waves that cause particles in rocks to vibrate at right angles to the direction of the waves

d. Epicenter – point on Earth’s surface directly above an earthquake’s focus

e. Surface waves – waves that move particles up and down and side to side in a swaying motion.

f. Surface waves cause most of the damage.

II. Locating an EpicenterA. Waves travel at different speeds; primary –

fastest, surface – slowest.B. Scientists use the different speeds of seismic

waves to find the distance to an earthquake epicenter.

C. Seismograph Stationsa. The farther apart the wave arrivals, the farther away the

epicenter is.

D. Epicenter Locationa. Needs to be recorded by three stations

b. Circles are drawn with the radius equaling the distance from the earthquake epicenter.

c. The point where all three intersect is the earthquake epicenter

III. Mapping Earth’s InteriorA. At different depths the speed and path of seismic

waves change. B. Changes mark the boundaries of the different

densities of the Earth’s layers. C. Structure of the Earth

a. Inner core – solid dense center, made mostly of iron, with some nickel and smaller amounts of oxygen, silicon, and sulfur.

b. Outer core – liquid layer made mainly of iron

c. Mantle – larges layer, made mostly of silicon, oxygen, magnesium, and iron.

d. Crust – thinnest, outermost layer made of silicon, aluminum, magnesium, and iron.

D. Moho Discontinuitya. Seismic waves speed up when they reach the bottom of the

crust

b. The boundary between the crust and the mantle is called the Moho discontinuity

E. Plasticlike Layera. Primary and secondary waves slow down

b. Then seismic waves speed up as they pass through the solid lower mantle

c. The denser the layer the faster the seismic waves can travel through

F. Shadow Zonea. Area on Earth where no seismic waves are detected

b. Secondary waves are stopped completely by the liquid outer core

c. Primary waves are slowed and bent by liquid outer core

G. Mantle Samplesa. Volcanic materials are a window to Earth’s interior.

b. Magma can break off and bring up pieces of mantle as it rises as lava.

H. Meteoritesa. Samples of the deep mantle and core have never been

collected

b. Rocky materials of the solar system are through to have formed at the same time

c. Study meteorites to understand Earth

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10.3Destruction by Eathquakes

EARTHQUAKES

I. Measuring Earthquakes