By: R. Wallace, WFHS Modified from D. Garcia, WFHS Earthquakes By: R. Wallace, WFHS Modified from D. Garcia, WFHS

Earthquakes and Plate tectonics The Earth experiences stress due to forces within the Earth.

Forces pull and push on the crust. Folds in sedimentary rocks, Australia Folds in sedimentary rocks, Australia Forces pull and push on the crust. Rocks will bend and stretch to a certain point (elastic limit) and will change shape and volume, move up, down or sideways When the force is great enough the rocks break, tilt and fold (deformation) Folds in sedimentary rock in Australia

3 types of stress *All can cause the rocks to fracture or crack. Compression – squeezes the rocks and pushes them deeper down and higher up. Tension – pulls on the rocks and cause it to be thinner in the middle and thicker at the ends. Shearing – pushes rocks into opposite directions causing twisting and tearing. *All can cause the rocks to fracture or crack.

Faulting: a break or crack along which rocks move due to stress Possible result are earthquakes, landslides, formation of mountains and valleys

Faulted rocks Hanging wall – the one part that moves Foot wall – the block of rock below the fault.

Types of Faults Normal Fault At divergent plate boundaries → Foot wall Hanging wall → Normal Fault At divergent plate boundaries Tension acts on the fault and causes the hanging wall to move down relative to the foot wall. Ex. Sierra Nevadas – (Fault Block Mt: Block of land slides down between 2 normal faults)

Types of Faults Reverse fault At convergent plate boundaries Hanging wall → Foot wall → Reverse fault At convergent plate boundaries Compression acts on the fault and causes the hanging wall to move up and over relative to the foot fall. Ex. Himalaya Mts contain many

Types of Faults Thrust fault: A special kind of Reverse Fault Compression causes the hanging wall to slide over the foot wall

Types of Faults Lateral fault (aka Strike Slip) At transform fault boundaries Shearing causes blocks of rocks to horizontally slide past each other Not much up and down motion. Irregular surface snag each other and twist Forces build up and the rocks break.

End of Part I

Earthquake Info What are Seismic waves? Energy waves that make the ground vibrate during an earthquake.

Seismic waves 3 types – primary, secondary and surface The point in the Earth’s interior where energy is released is the focus. Seismic waves travel outward from the focus.

Primary waves (P-waves) Cause rock particles to move in the same direction as the wave is moving. Push and pull compression and stretch

Secondary Waves (S-waves) Move through Earth by causing particles to move at right angles to the direction of the wave. SLOWER!!

Surface Waves aka Love waves (L-waves) The point on the Earth’s surface directly above the focus is the EPICENTER. Surface waves travel outward from the epicenter moving in an elliptical motion and cause most of the destruction during an earthquake.

Discovered in 1911 by A.E.H. Love

II. Locating an epicenter Primary waves are the fastest (and slow down through liquid layers) and secondary waves are slower (stop at liquids).

Locating an epicenter

Using this information, scientist can determine the epicenter Using this information, scientist can determine the epicenter. The farther apart the (time between) waves the farther away the epicenter is.

This is kind of like how GPS works… http://www.brainpop.com/science/earthsystem/earthquakes/

STEPS TO DETERMINE EPICENTER Analyze Richter Magnitude from 3 recording stations. After it converts to P and S wave graph, get distance. Where all 3 intersect → Epicenter

Mapping Earth’s Interior The speed and path of seismic waves change at certain depths marking the boundaries of the Earth’s layers. Seismic waves speed up when they reach the bottom of the crust. The boundary between the crust and the upper mantle is the Moho discontinuity.

TSUNAMI!! Dec 24, 2004 Thailand http://video.nationalgeographic.com/video/101-videos/tsunami-101

Measuring Richter (1930s) Mercalli Magnitude (size) of waves 1-10 Biggest reading recorded was in Chile 1960 - 9.5! Intensity Compares modern EQ with ones from the past (before Richter scale) I – XII (1-12) 1886 Charleston X

Major Earthquake Zones The Pacific Ring of Fire - The points surrounding the Pacific Plate where it is subducted under the surrounding plates. The Mid Ocean Ridge – A series of divergent boundaries Eurasian Melanesian – A series of convergent boundaries from Europe to SE Asia