# Earthquakes - PowerPoint PPT Presentation

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Earthquakes. Liz LaRosa http://www.middleschoolscience.com 2009 for my 5 th grade science class 2009. What is an earthquake?. Used to describe both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip

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Earthquakes

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## Earthquakes

Liz LaRosa http://www.middleschoolscience.com 2009

for my 5th grade science class 2009

### What is an earthquake?

• Used to describe both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip

• Caused by volcanic or magmatic activity,

• Caused by other sudden stress changes in the earth.

Strike-Slip

Dip Slip

### What causes earthquakes?

• Tectonic plates move past each other causing stress. Stress causes the rock to deform

• Elastic deformation – rock stretches then reaches a breaking point, releasing energy.

### Elastic Rebound – deformed rock goes back to its original shape

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

### Primary Waves (P Waves)

• A type of seismic wave that compresses and expands the ground

• The first wave to arrive at an earthquake

http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

### Secondary Waves (S Waves)

• A type of seismic wave that moves the ground up and down or side to side

http://daphne.meccahosting.com/~a0000e89/insideearth2.htm

### Surface Waves

• Move along the Earth’s surface

• Produces motion in the upper crust

• Motion can be up and down

• Motion can be around

• Motion can be back and forth

• Travel more slowly than S and P waves

• More destructive

### How do scientists calculate how far a location is from the epicenter of an earthquake?

• Scientists calculate the difference between arrival times of the P waves and S waves

• The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

### How are Earthquakes Measured? Mercalli Intensity Scale

Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

### Tsunamis

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

### Formation of a tsunami

http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

### Tsunami Warning System

http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

Magnitude 7.0 PERUWednesday, September 25, 2013 at 16:42:42 UTC

The Nazca Plate subducts beneath the South America plate at the Peru-Chile Trench offshore of western South America.

At the latitude of the earthquake, the Nazca Plate moves to the east-northeast with respect to the South America Plate with a velocity of about

70 mm/y.

South American Plate

Peru-Chile Trench

Nazca Plate

Magnitude 7.0 PERUWednesday, September 25, 2013 at 16:42:42 UTC

The record of the earthquake on the University of Portland seismometer (UPOR) is illustrated below. Portland is about 8355 km (~5192 miles, 75.27 degrees) from the location of this earthquake.

P-waves are compressional waves that travel a curved path through the mantle. The P-waves arrived to the seismometer in Portland 11 minutes and 44 seconds (704 seconds) after the earthquake.

PP waves are compressional waves that bounce off the Earth’s surface halfway between the earthquake and the seismic station.

Traveling the same path as the P-wave, the S-waves (shear waves) travel at a slower velocity, arriving 21 minutes and 25 seconds (1285 seconds) after the earthquake.

The surface waves are the last to arrive approximately 39 minutes after the earthquake, having traveled 8355 km to Portland along the surface of the Earth.

Magnitude 7.0 PERUWednesday, September 25, 2013 at 16:42:42 UTC

Shaking Intensity

The Modified Mercalli Intensity (MMI) scale depicts shaking severity. The area nearest the earthquake experienced strong shaking.

Perceived

Shaking

Extreme

Violent

Severe

Very Strong

Strong

Moderate

Light

Weak

Not Felt

Modified Mercalli Intensity

USGS Estimated shaking Intensity from M 7.0 Earthquake

Image courtesy of the US Geological Survey

Magnitude 7.0 PERUWednesday, September 25, 2013 at 16:42:42 UTC

This region experiences a large number of earthquakes.  Within 250 km of the epicenter, there have been 17 earthquakes of M6 and larger since 1973. The largest, a M8.4 earthquake of June 23, 2001, occurred along the plate boundary to the south.  It killed at least 74 people and destroyed over 17,000 homes.

Earthquakes are shallow at the Peru-Chile Trench and

increase to > 500 km depth towards the east as the Nazca

Plate subducts deeper beneath the South American Plate.

Earthquake