Earthquakes Earthquake – a vibration of earth produced by the rapid release of energy

Earth is not static, it is continually changing: (It is moving, sometimes it happens suddenly, sometime so slow it is imperceptible) Crustal uplift Horizontal movement

What has moved in this picture?

(Important vocabulary in understanding earthquakes) Focus – the point where an earthquake starts, where the actual “break” takes place Epicenter – location on the surface directly above the focus

The movement of the Earth is associated with Faults, fractures in the Earth where movement has occurred Strike-slip Normal reverse Types of faults:

Normal Fault Example Dixie Valley-Fairview Peaks, Nevada earthquake December 16, 1954

Normal Fault - Mackay, Idaho

Strike-slip Fault Example

Reverse

Each fault behaves differently... Creep- slow movement

Slump- sudden movement

Causes for an Earthquake Elastic Rebound – The spring back of rock into its original place Animation nimation.php?flash_title=Elastic+Rebound&flas h_file=elasticrebound&flash_width=300&flash_ height=350

Measuring Earthquakes Seismology – The study of earthquakes Which one is: A- the instrument that records earthquakes B- the paper print-out of the movement of an earthquake C- the person who studies earthquakes

Earthquake Location Ancient Chinese “seismograph” Tools for measuring earthquakes have been around for a long time The jar is filled with water. As the earth shakes and water is spilled the amt. is measured

Now we use sensitive machines which measure the energy waves released. Measuring these waves we can determine the speed and distance they have traveled and determine the epicenter.

Surface Waves/L waves These waves are the most destructive. They move along the surface in both vertical and horizontal directions

Body Waves (under the surface) Primary Wave (P wave) They are the fastest They arrive first Have a “push/pull” motion Secondary Wave (S wave) They are about ½ as fast as P waves They “shake” particles at right angles They can not move through gases and liquids

Review layers of Earth’s Interior

(review what the interior of the Earth is like)

Note: the P waves are somewhat deflected by the different layers of the interior and the S wave will not travel through the liquid outer core

Why are the interior waves “bent” when they reach the core?

Which wave arrives first? Second? Last? Which is the largest wave?

Which city is closest to the epicenter? The shorter the time between The first P wave and the first S wave indicates the distance

Complete the “Locating an Earthquake” activity Practice work for the activity follows on the next 3 slides

Recording the arrival times of the waves Recording the distance covered

We can determine the distance from the recording station to The epicenter but we do not know the direction A minimum of 3 stations must Record in order to locate the epicenter A circle is drawn around the Seismograph station with the Radius equal to the distance The waves have traveled Where all 3 circle meet Is the epicenter

Using a Travel Time Graph 1.Find the time between the first P wave and the first S wave 2.Find the equivalent time spread between the P and S wave curves on the graph. 3.Follow line to the X axis and you have the distance from the seismograph to the epicenter

Measuring Earthquakes Intensity – a measure of the amount of earthquake shaking at a given location based on the amount of damage. This is visual, not a measured amt.

Modified Marcalli Scale Did you feel it? Intensity felt by the earthquake Based on structural damage gov/earthquakes/dyfi/ gov/earthquakes/dyfi/

Magnitude – a measure of the size of seismic waves, or the amt. of energy released from the source. This is a number

Richter Scale – measures wave amplitude (height) Based on log scale. Each Magnitude is 10 times stronger than the last. So an earthquake magnitude of 5.5 has 10 X more ground shaking than one of magnitude of 4.5

Moment Magnitude A more precise means of measuring earthquakes. Based on three factors: surface area of the fault X average displacement along the fault X rigidity of rock Together these factors provide a measure of how much energy rock can store before it suddenly slips and releases this energy during an earthquake.

Each Unit of Magnitude increase corresponds to: – A 10 X increase in wave amplitude – A 30 X increase in the amount of energy: a 6.5 releases 30 X more energy than a 5.5 and 900 X more energy (30 x 30) than a 4.5

Destruction from Earthquakes Intensity and duration of the vibrations Nature of the material on which the structure is built Design of the structure

Liquefaction Where loosely consolidated sediments are saturated with water will turn to liquid during an earthquake Japan Earthquake m/watch?v=u8hfCN6k3 YE m/watch?v=u8hfCN6k3 YE Animation gov/learn/animations/ gov/learn/animations/ &feature=related

Result of liquefaction

Most deaths associated with earthquakes are caused by the results of the quake Fire Tsunamis landslides

Events triggered by earthquakes

Earthquake Effects - Tsunamis Photograph Credit: Henry Helbush. Source: National Geophysical Data Center 1957 Aleutian Tsunami

Tsunamis Japan Tsunami Before and After /watch?v=zduhngJvCAY /watch?v=zduhngJvCAY Japan Tsunami (watch 1 st half) com/watch?v=8IQZ2mdN zP4&feature=fvwrelhttp:// com/watch?v=8IQZ2mdN zP4&feature=fvwrel Japan Tsunami (from far away) /watch?v=oKzEQwAx0m8 &feature=related /watch?v=oKzEQwAx0m8 &feature=related During an earthquake the ocean floor is displaced along a normal or thrust fault, the displaced causes a Tsunami An underwater landslide can also cause a Tsunami

Tsunamis Travel at 500 to 950 Kmph – 310 to 590 mph Largest Tsunami Recorded was 1720 feet tall, about the length as 6 football fields July 9, 1958 Lituya Bay, Alaska Are Tsunamis tidal waves? What areas are protected by the tsunami warning system?

Earthquake Effects - Landslides Turnagain Heights, Alaska,1964 (upper left inset); Santa Cruz Mtns, California, 1989 Source: National Geophysical Data Center

Madison Landslide.74 miles Landslide was caused by an Earthquake in 1959, epicenter in NW Yellowstone. Earthquake caused the dolomite buttress that was supporting the mountain side to break, causing a landslide. The picture is taken from atop the debris pile. Original valley floor is 300 ft below. The material moved in 1 min. The material is enough to build a one lane 3 ft deep round from here to New York City.

Two diagrams showing cross section of the valley. Photo on the left is taken from atop the debris showing the opening of the valley. Landslide is off photo to the left.

Earthquake Safety

Earthquake Prediction Scientists do not understand enough about how and where earthquakes will occur to make predictions Scientists look at where earthquakes have not happened in a long time and they study seismographs to see if there is any pattern