EARTHQUAKE

Earthquakes 

Shaking of earth due to movement of rocks along a fault.

Rocks under stress accumulate strain energy over time.

When stress exceeds strength of rocks, rock breaks.

 

Types of earthquakeTectonic earthquakes

these occur when rocks in the earth’s crust break due to geological forces created by the movement of tectonic plates.

Volcanic earthquakes occur in conjunction with volcanic

activity.

Collapse earthquakesare small earthquakes in

underground caverns and mines.Explosion earthquakes

result from the explosion of nuclear and chemical devices.

Focus and Epicenter• FOCUS = place deep within the Earth and along the fault where rupture occurs

• EPICENTER = geographic point on surface directly above focus

Seismologists are scientists that study earthquakes and seismic waves.

Seismic Waves – shock waves of energy sent out as the crust shakes

Seismograph is the instrument they use to obtain a record of seismic waves from all over the world.

Seismograms zigzag line made by a seismograph.

• Amplitude of seismic waves (how much rock moves or vibrates)

• Distance to the epicenter

• Earthquake direction

Types of seismic waves

1. Body waves -- travel through interior

2. Surface waves -- travel on surface of earth

Slowest

2 kinds of Body Waves1.P-waves (Primary waves)Fastest of the three waves and the first

detected by seismographs.• Can travel through Earth’s interior in less than

an hour• Pass through solids & liquids• As they pass through the liquid of the outer

core they change directions• As they return to Earth’s surface they cause

back-and-forth motions of rock

2. S-waves (Secondary waves)• Travel slightly slower than P waves• When they reach Earth’s surface they

cause it to move up and down• They can travel ONLY through solids• When they pass through the mantle to

the liquid core they lose their energy and do not return to the surface

2 types of Surface waves

1.Love waves– that move like S waves but only horizontally.

2.Rayleigh waves– that move both horizontally and vertically in a vertical plane pointed in the direction of travel

EARTHQUAKE WAVES

P waves move through solids & liquids

S waves move through solids only!!!

EARTHQUAKE DAMAGE• Landsides

• Building damage

• Liquefaction

LIQUEFACTION

• Results in a loss of soil strength & the ability of the soil to support weight

when a solid (sand and soil) becomes saturated with water and acts like a heavy liquid

EARTHQUAKE DAMAGEMost caused by SURFACE waves (arrive last)

• Foreshocks are small bursts of shaking that may precede a large earthquake.

• Aftershocks are small tremors that follow an earthquake, lasting for hours or even days after the earthquake.

EARTHQUAKE INTENSITY

Modified Mercalli scale= measurement of damage to structures

• From I to XII (Roman numerals)

• Descriptive, changes withdistance from epicenter

• Can change from location to location

What you need:• Your senses!

measures damage to man-made structures at certain location

EARTHQUAKE WAVES

P waves move through solids & liquids

S waves move through solids only!!!

EARTHQUAKE WAVES

Lets test your understanding!!

Is this a P or an S wave?

P wave!

S Wave

EARTHQUAKE INTENSITY

Modified Mercalli scale= measurement of damage to structures

• From I to XII (Roman numerals)

• Descriptive, changes withdistance from epicenter

• Can change from location to location

What you need:• Your senses!

measures damage to man-made structures at certain location

http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

EARTHQUAKE MAGNITUDE measures the size of seismic waves

the energy released by the earthquake

Richter scale=measurement of energy released based upon wave amplitude (size of vibration)

• <2 to ~10

• Amplitude of wave goes up by 10 (Logarithmic scale)

VOLCANOES

VOLCANOES

• An opening in Earth’s surface through which melted rock, hot gases, rock fragments, and ash burst forth, or erupt

• Volcano – comes from the ancient Roman god of fire, Vulcan

• Start 37 – 100 miles below surface• Rock melts and is called Magma