More Earth Science

LandformsEarthquakesSeismic WavesShadow Zone

Landforms

Mountains

• A mass of rock rising more than 600 meters above the surrounding land

• Relief vs. Elevation

Types of Mountains

Fold Mountain

Fold Mountains

• Usually made mostly of sedimentary rock folded by compression forces

• These are the tallest and most common of all mountains

Examples of Fold Mountains

Appalachian Mountains

Rocky Mountains

Alps

Himalaya Mountains

Fault-Block Mountain

Fault Block Mountain Ranges are cause by a series of normal faults

Examples of Fault block Mountain

ranges

Sierra Nevada Mountains, CA

Grand Tetons, WY

Wasatch Mountains, Utah

When the Earth SHAKES

Earthquakes

What causes earthquakes?

• Volcanic eruptions can cause earthquakes but most earthquakes are caused by FAULTING

• These are often called TECTONIC earthquakes

Theory VS. Law• A THEORY is a logical idea that has

not been proven directly but it often can be proved mathematically

• It is a working set of rules that define a body of knowledge

• A LAW is observable and can be proven- to a point. Nothing is 100% sure in a Universe as vast as ours

Elastic Rebound Theory

The Elastic Rebound Theory was first proposed by American geologist Harry Fielding Reid after the 1906 San Francisco Earthquake

Elastic Rebound

• The sudden release of progressively stored strain in rocks, resulting in movement along a fault

• After the stress becomes too great, the rock layers break, vibrating back and forth until eventually coming to a rest

• As the rock layers are shaking back and forth they send out waves of vibration called Seismic Waves

• “Seismic” always has to do with earthquake activity

Seismic Waves are waves of vibration sent out in all

directions from the FOCUS

• FocusThe point below the surface where the rock layers break and move

• EpicenterThe point on the surface, directly above the focus. Where the greatest damage usually occurs

Fault

Focus

Epicenter

Seismic Waves

Measuring Earthquakes

Charles Richter26 April 1900 –

30 September 1985

Seismograph

A machine that measures earthquake (seismic) waves

Zhang Heng seismograph

is almost 2000 yrs old

Early Seismograph

Operates on the principle of Newton’s First Law

SeismogramThe recorded information of earthquake

waves

The Richter Scale is based on MAGNITUDE

Seismogram

Each # is TEN TIMES larger than the # before it…

Magnitude 1

Magnitude 2

Magnitude 3

Pennies as an example:Mag. 1 = 1 pennyMag. 2 = 10 penniesMag 3 = 100 penniesMag. 4 = 1000 penniesMag. 5 = 10,000 penniesMag. 6 = 100,000 penniesMag. 7 = 1,000,000 penniesMag. 8 = 10,000,000 penniesMag. 9 = 100,000,000 penniesMag. 10 = 1,000,000,000 pennies(that’s $10 million in pennies!!)

Richter Magnitudes Earthquake Effects

Less than 3.5 Generally not felt 3.5-5.4 Often felt, little

damageUnder 6.0 Slight damage to

buildings6.1-6.9 Destructive to about

100 km from epicenter7.0-7.9 Major earthquake.

Can cause serious damage8 or greater Large earthquake.

Serious damage for hundreds of km

Anatomy of a basic wave

• Crest – the highest point on a wave (A, F)

• Trough – the lowest point on a wave (D, I)

• Amplitude – the distance between the midpoint & crest or trough

• Wavelength – distance between any two successive points on a wave

• Frequency - # of vibrations/ second (Hertz)

Types of Seismic Waves

Body Waves are waves that travel through the body of the earth

Surface waves only travel along the surface of earth

Body Waves

Primary WavesAKA P-Wave

• Type of Longitudinal Wave

• Causes back and forth motion

• Follows the same direction as the energy transfer

P-Waves

• Type of COMPRESSIONAL wave (like sound)

• Will travel through solid, liquid or gas• Travels at: • 7.8 – 8.5 kps in mantle• 7.2 kps in oceanic crust• 3.5 kps in continental crust

Primary Wave•http://sunshine.chpc.utah.edu/labs/seismic/surface.swf

Secondary WaveAKA S-Wave

• Particle motion is perpendicular to direction of energy transfer

• Transverse or Shear Wave

• Will travel only through solids

• Travels 4 – 5 kps

Secondary Wave•http://sunshine.chpc.utah.edu/labs/seismic/surface.swf

Surface Waves

• Two main types of surface waves:

• Love Wave

• Rayleigh Wave

• Recent evidence show s that L-Waves attenuate (gradually disappear) more slowly in older rock (eastern US) and more quickly in younger rock (western US)

Love Wave•http://sunshine.chpc.utah.edu/labs/seismic/surface.swf

Love Waves

• Love Waves travel less than 4 kps

• Move side-to-side; like a snake

• Cause the most damage

Seismic Waves

Seismogram with the P-Wave, S-Wave and L-Wave

Seismic Risk in the US

Triangulation

Refraction

Refraction of seismic waves within the Earth

Zone between about 105 degrees & 145 degreesis the Shadow Zone

105 degrees145 degrees

Focus

Shadow Zone

How Hawaiian Islands are formed