Predictpage 239 • Each year there are approximately ______ earthquakes detected around the world. • In the United States, the state with the most earthquakes on average is ________ • Every year, earthquakes cause ________ of dollars in damage in the United States. • Most earthquakes only last for several _________ of time. 500,000 Alaska billions seconds
Earthquake Frequency • When did the last earthquake occur? • More than 3 million earthquakes with Richter magnitudes of 1 or more occur each year. • World Earthquakes • Midwest Earthquakes • Small magnitude earthquakes happen many times a day – about one every 10 seconds!
Japan March 11, 2011 A magnitude-9 earthquake shook northeastern Japan, unleashing a savage tsunami The effects of the great earthquake were felt around the world Tsunami debris continues to wash up on North American beaches two years later.
Haiti January 12, 2010 Magnitude – 7.0 The depth of this earthquake in Haiti was very shallow, meaning that the energy that was released is very close to the surface. The US Geological survey report that (as of the 5th of February, 2010) there have been 59 aftershock reporting of magnitude 4.5 or greater.
Sumatra, IndonesiaDecember 26, 2004 9.1-magnitude undersea earthquake rumbled near Sumatra and stretched 750 miles to the north. Was the third largest earthquake in the world since 1900. The resulting tsunami devastated coastlines along the Indian Ocean, with tsunami waves up to 100 feet high.
What is an earthquake? • Earthquakes are ground movements that occur when blocks of rock in Earth move suddenly and release energy. • Energy released as seismic waves which cause the ground to shake and tremble
What is an Earthquake? Place within Earth along a fault at which the first motion of an earthquake occurs. Directly above the focus on Earth’s surface. A break in Earth’s crust along which blocks of rock move. • Focus • Epicenter • Fault
Visualize it! Epicenter Fault Focus
What causes Earthquakes? Most earthquakes occur near the boundaries of tectonic plates. (a) Along a fault rocks are pushed or pulled in different directions at different speeds. (b&c) As stress increases and energy builds within the rock, the rock deforms, deformation, but remains locked in place. (c) Too much stress causes the rock to break and rebound to its original shape, elastic rebound, releasing energy – an Earthquake!
Where do Earthquakes occur? Most earthquakes happen at or near tectonic plate boundaries
Divergent Boundaries • Plates pull apart • Stretching creates thin rock and tension causing normal faults • Earthquakes here tend to be shallow (no more than 20 km deep) • Ex. Mid-ocean ridge
Convergent Boundaries • Plates collide • Squeezing shortens and compresses the rock • Rocks are thrust over one another causing reverse faults • Plates can crumple up to form mountains or subduct underneath the other plate • Strong earthquakes - subduction earthquakes at depths of up to 700 km
Transform Boundaries • Plates slide past each other horizontally • Shear stress occurs when rocks on both sides are broken as they grind past one another • Strike-slip faults are common at transform boundaries • Relatively shallow earthquakes within upper 50 km of crust
Boundaries • At divergent boundaries, earthquakes are common along ______________ faults. • At convergent boundaries, earthquakes are common along _____________ faults. • At transform boundaries, earthquakes are common along ______________ faults. normal reverse Strike-slip
Major EarthquakesWhat type of earthquakes do you think these were? • Japan - The Pacific oceanic plate slipped under the Asian continental plate. • Haiti – The Caribbean plate creeps eastward at 2 cm a year, but the Enriquillo-Plaintain Garden fault hasn’t moved in more than 200 years. Occurred 6.2 miles beneath surface. • Sumatra - The portion of the fault that ruptured lies deep in the earth's crust, in places as much as 50 km (31 miles) below the ocean floor. There the two tectonic plates, which had been stuck together, suddenly broke free, the upper plate sliding back upward and to the west by as much as 20 m (65 feet) along the plate boundary.
What are some effects of Earthquakes? People and Structures Tsunamis Under sea earthquake Displaces enormous amount of water Waves travel outwards (800 km/h) in all directions Size of waves increase as they approach land Can be taller than 30 m Destruction can cause drownings and town destruction Floods Polluted water Large amount of debris • Building collapse • Injury/loss of life • Fires • Gas leaks • Floods • Polluted water • Clean up • Roadways, homes, bridges
Identify List some of the hazards associated with earthquakes on land and underwater ON LAND UNDERWATER
Predict True • Earthquakes often occur along faults. • Earthquakes produce two main kinds of seismic waves. • More than one kind of scale can be used to measure the magnitude of an earthquake. • Older buildings tend to withstand earthquakes better than newer buildings. True True False
What happens during an earthquake? • Stress build up along fault • Rocks split suddenly • Energy is released in seismic waves • Seismic waves travel through earth and along surface causing ground motion • An earthquake is felt.
What causes the strength of an Earthquake? • Based on the energy that is released as rock break and return to an undeformed shape.
Visualize it How are the ripples that are moving through the water in this pond similar to seismic waves that travel through Earth? How are they different?
What are two kinds of seismic waves? • Body Waves • Waves travel through Earth’s interior • Move faster • Surface Waves • Travel along the surface of Earth • Cause more damage
Body Waves P Waves S Waves shear waves Also called secondary waves Slower than P waves Move rock from side to side Cannot travel through liquid parts of Earth • pressure waves, are the fastest • Also called primary waves because they are detected first • Can travel through solids, liquids and gases • P waves cause rocks to move back and forth in the direction the wave is traveling
Surface Waves Back and Forth Rolling up-and-down Occurs in same direction the wave is traveling Dies out with depth • Perpendicular to the direction in which the wave is traveling
What types of waves are these? How could you demonstrate the other types of waves?
How are seismic waves measured? • Seismometers are used to record seismic waves • When waves reach the seismometer it produces a seismogram • A seismogram is a tracing of earthquake motion • Seismograms are plotted on a graph and scientists use the graph to pinpoint the location of the earthquake epicenter.
P waves are first recorded. The difference between the arrival times of P waves and S waves, lag time, increases as the waves travel further from the point of origin. Lag time is used to find the earthquake epicenter. Seismograph
How is the earthquake epicenter located? • The lag time tells scientists how far waves have traveled from the epicenter • The epicenter can be found by drawing circles (based off lag time) around the seismometer stations on a map and tracking where each of the three circles intersect. • This process is called Triangulation.
How is earthquake magnitude measured? • The height of the waves on a seismogram indicate the amount of ground motion which can be used to calculate magnitude • Magnitude is the amount of energy released by an earthquake. • Richter scale • Moment magnitude scale
How is earthquake magnitudemeasured? Richter Moment Magnitude Scale Measures earthquake strength based on... Size of the area of the fault Average distance fault moves Rigidity of rocks in fault Better at measuring large earthquakes • Measures ground motion from an earthquake • Each time the magnitude increases by one unit, the measured ground motion is 10 times greater • Ex. An earthquake measuring 5.0 produces 10x as much ground motion as a 4.0 earthquake
How is earthquake intensity measured? • The effects of an earthquake and how it is felt by people on the surface are known as the earthquake’s intensity • What’s the difference between magnitude and intensity? • Modified Mercalli scale describes intensity • Ranges from I to XII
DAMAGE CONTROL • What factors determine the effects of an earthquake? • Magnitude • Local Geology • Distance from Epicenter • Building Construction
DAMAGE CONTROL • Magnitude • magnitude damage • Local Geology • Material waves travel through • Liquefactioncan cause ground to settle. Structures tilt or collapse • Distance from Epicenter • Distance from epicenter Wave intensity • Building Construction • More flexible structures more likely to survive strong ground shakes • Which are more flexible? wood concrete brick steel wood steel
Building a SeismometerHISTORY • Magnitude is measuring using the Richter scale, which was invented by Charles Richter. The Richter scale rates the magnitude of earthquakes based on the size of their seismic waves, as measured with a seismometer. Dr. Richter realized that some earthquakes produced small waves and others produced large waves. To make it easier to compare very large and very small waves, Richter used logarithms of the wave heights. A wave 1mm (1,000 microns) high on a seismogram has a magnitude of 3 (because 1,000 is ten to the third power). A wave 10mm (10,000 microns) high has a magnitude of 4 (ten to the fourth power). A magnitude-4 earthquake causes shaking 10 times greater in amplitude than a magnitude-3 earthquake. • There should never be an earthquake too much greater than magnitude-9 because such a quake would require a fault bigger than any that currently exists on Earth.
Building a Seismometer seismometer
Building a SeismometerEngineering and Design • Things you will need: • Shoebox • Ruler • Scissors • Paper • Tape • Rubber bands • Fine point marker/pen • Yarn or string • Cup • Clay
Building a Seismometer • Your engineering task is to create, in your group, your own version of a seismometer with the provided tools. • You do not need to use all the tools, but the end product needs to indicate seismic activity when the “earthquake” (table shaking) occurs.