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