Earthquakes

What are Earthquakes?  Earthquakes are

What are Earthquakes?  As the plates move they put forces on themselves and each other. 

What are Earthquakes  When the break occurs, the stress is released as energy which moves through the Earth ______________________________________, which we feel and call an earthquake.

What causes the stress?   There are three main forces that drive deformation within the Earth and create the stress that causes earthquakes. 

Which of the following things are elastic?  Pasta  Rubber bands  Super balls  Rocks  Plastic  Metal  Dirt

Elasticity  Elasticity is a physical property of materials which return to their original shape after the stress that caused their deformation is no longer applied  What does that mean?

Elasticity   We can use the elastic properties of rock to explain how energy is stored and released within the Earth’s crust.

Elastic Rebound  Explains how energy is stored in rocks  Rocks bend until the strength of the rock is exceeded  Rupture occurs and the rocks quickly rebound to an undeformed shape  Energy is released in waves that radiate outward from the fault

More Stuff About Earthquakes

Faults  Any stress on the plates can cause an earthquake if the elastic limit is reached.  Each type of stress, however, results in a specific type of fault.

Normal Fault =

Reverse Fault  AKA Thrust Fault  =

Strike Slip = No change in elevation, rock slides past one another.

Focus and Epicenter  Focus:  Epicenter:

Types of Earthquakes  - Foci are less than 70 km depth.  - Foci are between 70 and 300 km depth.  - Foci are greater than 300 km.

Measuring Earthquakes

How do we measure an earthquake?  There are two main scales with which we can measure an earthquake.  Mercalli  Richter

The Mercalli Scale  In 1902 Guiseppe Mercalli devised a scale for measuring the intensity of an earthquake by  In 1931 seismologists modified his scale to adapt to modern American building standards.  We can use Mercalli’s modified scale to find the epicenter of an earthquake.

IBarely felt IIFelt by a few sensitive people, some suspended objects may swing IIISlightly felt indoors as though a large truck were passing IVFelt indoors by many people, most suspended objects swing, windows and dishes rattle, standing autos rock VFelt by almost everyone, sleeping people are awakened, dishes and windows break VIFelt by everyone, some are frightened and run outside, some chimneys break, some furniture moves, slight damage VIIConsiderable damage in poorly built structures, felt by people driving, most are frightened and run outside VIIISlight damage to well built structures, poorly built structures are heavily damaged, walls, chimneys, monuments fall IXUnderground pipes break, foundations of buildings are damaged and buildings shift off foundations, considerable damage to well built structures XFew structures survive, most foundations destroyed, water moved out of banks of rivers and lakes, avalanches and rockslides, railroads are bent XIFew structures remain standing, total panic, large cracks in the ground XIITotal destruction, objects thrown into the air, the land appears to be liquid and is visibly rolling like waves

The Richter Scale  Prior to 1935 earthquakes were measured by using the Mercalli Scale.  Charles Richter (1935) created a numerical method based on the __________________________________________ recorded on a seismogram and the distance from the epicenter.

Richter Scale  Richter magnitudes are based on a logarithmic scale, base 10  This means that for each whole number you go up on the Richter scale the strength of the earthquake goes up ten times.

Magnitude Examples  A magnitude of 3 is ____ times ____________ than a magnitude of 2  A magnitude of 5 is ____ times ____________ than a magnitude of 7  A magnitude of 6 is ____ times ____________ than a magnitude of 2

M1 M2 M3

So, what does it mean?  Think of it in terms of energy released by explosives:  A magnitude 1 earthquake releases as much energy as blowing up 6 ounces of TNT  A magnitude 8 earthquake releases as much energy as blowing up 6 million tons of TNT!  That is roughly 6 nuclear bombs!

Measuring Via Richter Scale  What do we need to determine the size of the earthquake?  Seismograph  Determine the ________________________________________  Determine ___________________________________________  Nomogram  Find the S-P interval  Find the amplitude  Draw a line that connects the above points to find magnitude

Example

Measuring Earthquakes Waves Edition

Seismic Waves  There are three types of waves that are created when stress is released as energy in earthquakes

P-waves  Primary waves are the fastest of the three waves and the first detected by seismographs.  Move at about 3.5 miles/second  They are able to move through both liquid and solid rock.  P waves, like sound waves, are longitudinal waves, which means that they compress and expand matter as they move through it.

S-waves  Secondary waves are the waves directly following the P waves.  Move at about 2.1 miles/second  S waves move through solids only  Serpentine movement

Body Waves  Both P and S waves are called body waves because they move within the Earth's interior.

Surface Waves Travel just below or along the ground’s surface  Most damaging waves!  Move at about 1.2 miles/second  Two Types:  L – Waves  R - Waves

Surface Waves  L – waves, or Love Waves, move parallel to the Earth's surface and perpendicular to the direction of wave propagation.  R – waves, or Rayleigh waves, move in an elliptical motion, producing both a vertical and horizontal component of motion in the direction of wave propagation.