PowerPoint Presentation - Earthquakes

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29 Νοε 2013 (πριν από 3 χρόνια και 4 μήνες)

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Earthquakes

Ch. 5

Forces on Earth’s Crust


Stress is the force that acts in an
area of rock to change its shape or
volume


Types of stress


Tension
-

pulling crust


Compression
-

squeezing crust


Shearing
-

pushes in opposite directions


Causes rock to break, slip, change shape

Tension

Compression

Shearing

Faults


Faults are breaks in the Earth’s crust


Hanging Wall
-

a block of crust that
forms the upper half of a fault


Footwall
-

a block of crust that forms
the lower half of a fault

Faults


Types of Faults


Normal fault
-

at divergent boundaries

Faults


Types of Faults


Reverse fault
-

at convergent boundaries

Faults


Types of Faults


Strike
-
Slip fault
-

at transform boundaries

Folding Earth’s Crust


Forces change a flat plain into
anticlines, synclines, folded mountains


Caused by compression

Stretching Earth’s Crust


Forces change a flat plain into
fault
-
block mountains


Caused by tension

Seismic Waves


Vibrations that carry energy from
an earthquake

Types of Seismic Waves


P waves compress and expand the
ground

Types of Seismic Waves


S waves move side to side, and
some times up and down

Types of Seismic Waves


Surface waves move slowly, but
causes the most damage

Earthquakes


Results from sudden movement
along a fault


Focus
-

area beneath the Earth’s
surface where the earthquake
begins


Epicenter
-

place on Earth’s surface
directly above the focus

Measuring Earthquakes


Seismograph
-

instrument used to
record seismic waves on a
seismogram

Earthquake Scales


Mercalli Scale
-

measures intensity at
a specific location


Richter Scale
-

measures
earthquake’s magnitude (size of
seismic waves)


Moment Magnitude Scale
-

measures earthquake’s energy

Locating Epicenter


Determine distance with different
speeds of P and S waves


Need three seismic stations

Monitoring Earthquakes


Geologists look for increased
pressure along a fault


Instruments measure changes in
elevation, tilting of land, and
ground movements

Earthquake Risk


Geologists determine earthquake
risk by


Locating active faults


Past earthquakes


Amount of damage from past
earthquakes

Earthquake Damage


Shaking
-

ground moves and is
affected by type of rock or soil


Liquefaction
-

loose, soft soil turns
into liquid mud


Aftershocks
-

another earthquake
after a big earthquake


Tsunami
-

water displaced by
earthquake

Safer Buildings


Make buildings stronger and more
flexible

Safety Features


Flexible Joints
-

prevent gas pipes
and water mains from breaking


Base Isolator
-

absorbs seismic
waves


Mass Damper and Active Tendon
System
-

shifts center of gravity to
prevent collapse


Steel Cross
-
braces
-

makes building
stronger

1989 Loma Prieta Earthquake

1989 Loma Prieta Earthquake

1989 Loma Prieta Earthquake