Plate Tectonics and Earth’s Structure

Susan MeathCohort 21/Tech 290

9/17/08

StandardsPlate Tectonics and Earth’s Structure

1e. Students know major geologic events, such as earthquakes, volcanic eruptions, and mountain building, results from plate motions.

Types of Earthquakes

- Convergent Boundary- Divergent Boundary

-Transform Boundary- Seismic waves

Convergent Boundary

Continental-Continental Convergence

Himalayan mountain range When two continents meet head-on, neither is subducted Crust tends to buckle and be pushed upward or sidewaysThe collision of India into Asia 50 million years ago caused the Eurasian Plate

Oceanic-Continental Convergence

When these two plates collide the more dense oceanic plate subducts and is melted in the mantle. Earthquakes occur deep below the surface.Ocean crust is destroyed in subduction zones.Ocean crust is always younger than continental crust.

Oceanic-Oceanic Convergence

- Two ocean plates collide. - Melting destroys one plate. - The low-density liquid rock rise to the surface causing a volcanic island arch to form. - Above the subduction zone a deep trench forms.

Divergent Boundary

Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle.

Mid-Atlantic Ridge

The Mid-Atlantic Ridge, splits nearly the entire Atlantic Ocean north to south. The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year (cm/yr), or 25 km in a million years.The volcanic country of Iceland straddles the Mid-Atlantic Ridge. Iceland is splitting along the spreading center.

Krafla Volcano Lava fountains spouting from eruptive fissures during the October 1980 eruption. Existing ground cracks have widened and new ones appear every few months. From 1975 to 1984, numerous episodes of rifting (surface cracking) took place along the Krafla fissure zone.Some of these rifting events were accompanied by volcanic activity.

Red SeaA young divergent plate boundary that is actively forming the Red Sea.The Arabian penninsula and Africa were once linked to form a single continent, they are now being ripped apart. The white arrows show the directions the two plates are moving. You can see that a new ocean, the Red Sea is being formed as they separate.

Transform Boundary

San Andreas FaultRight-lateral strike-slip fault The San Andreas connects a divergent boundary in the Gulf of California with the Cascadia subduction zone. The San Andreas fault is the 800 mile long boundary between the Pacific and North American Plates.At its deepest, the San Andreas extends 10 miles beneath the ground.

Types of Faults

Transform faults can be distinguished from the typical strike-slip faults A strike-slip fault is a simple offset Transform fault is formed between two different plates, each moving away from the spreading center of a divergent plate boundary. Transform faults cut continental lithosphere.

Fracture ZonesBlanco

Mendocino

Murray

Molokai

Seismic Waves

The waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.

P-Wave

The first kind of body wave is the P wave or primary waveThis is the fastest kind of seismic wave, and, consequently, the first to 'arrive' at a seismic station. The P wave can move through solid rock and fluidsSometimes animals can hear the P waves of an earthquake.

S-WaveThe second type of body wave is the S wave or secondary waveIt is this property of S waves that led seismologists to conclude that the Earth's outer core is a liquid.Waves move rock particles up and down, or side-to-side--perpindicular to the direction that the wave is traveling in An S wave is slower than a P wave and can only move through solid rock,

Love Wave and Rayleigh Wave

It's the fastest surface wave and moves the ground from side-to-side. Confined to the surface of the crust, Love waves produce entirely horizontal motion.Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean.Most of the shaking felt from an earthquake is due to the Rayleigh wave,

References http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor15039288 http://geology.com/nsta/convergent-plate-boundaries. http://scign.jpl.nasa.gov/learn_unix/plate4.htmhttp://www.classzone.com/books/earth_science/terc/content/visualizations/es0803/es0803page01.cfm?chapter_no=visualizationhttp://www.geo.mtu.edu/UPSeis/waves.html