More Earth Science Landforms Earthquakes Seismic Waves Shadow 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

Focus The point below the surface where the rock layers break and move Epicenter The point on the surface, directly above the focus. Where the greatest damage usually occurs

Fault Focus Epicenter Seismic Waves

Measuring Earthquakes

Charles Richter 26 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

Seismogram The 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 penny Mag. 2 = 10 pennies Mag 3 = 100 pennies Mag. 4 = 1000 pennies Mag. 5 = 10,000 pennies Mag. 6 = 100,000 pennies Mag. 7 = 1,000,000 pennies Mag. 8 = 10,000,000 pennies Mag. 9 = 100,000,000 pennies Mag. 10 = 1,000,000,000 pennies (that’s $10 million in pennies!!)

Richter Magnitudes Earthquake Effects Less than 3.5 Generally not felt Often felt, little damage Under 6.0 Slight damage to buildings Destructive to about 100 km from epicenter Major earthquake. Can cause serious damage 8 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 Waves AKA 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

Secondary Wave AKA 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

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

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 degrees is the Shadow Zone

105 degrees 145 degrees Focus

Shadow Zone

How Hawaiian Islands are formed