What is an Earthquake? The shaking of earth’s crust caused by the release of energy

Deadliest Earthquakes Video What causes Earthquakes? How are earthquakes detected? Measured? Describe the different types of faults, and their effects. Can earthquakes be detected early to prevent damage? What are silent quakes? Interesting facts on Haiti, San Andreas Fault, Chile Earthquake

Waves Earthquakes shake the earth by releasing waves of energy There are 3 different wave types 1. P waves 2. S waves 3. L waves

P Waves ComPressional or Primary waves Cause the ground to expand and contract

S Waves Secondary or Shear waves Cause the land to move at right angles to the direction of the wave

L Waves Occur when the S and P waves reach the surface Make the ground move like ripples in a pond

Seismographs Instrument that records earthquake waves and measures their strength Seismogram: Collects earthquake data P waves are first, then S waves follow

What are the P and S wave arrival times? What is the difference between them in seconds 5sec

Earthquake Terms Focus: the point at which the first plate movement occurs and the energy is released Epicenter: the point on the surface directly above the focus

Locating Earthquakes

Time Travel Graph Used to calculate the distance from the seismograph to the epicenter Use interval times of p & s arrival times

Cont’d Each seismograph station has a different epicenter distance Use 3 stations, the point at which all those distances intersect is the epicenter

The Richter Scale Measures the amount of energy released by an earthquake (seismographs) Logarithmic Scale  Increases ten fold Scale

The Mercalli Scale Describes the intensity/severity of an earthquakes effect Uses Roman Numerals 1 (I) through 12 (XII)

Earthquake Damage 1. Ground shaking  release of energy & movement of waves, buildings cannot withstand damage 2. Foundation failure  results from shaking, disrupts soil, causes buildings to collapse

The Earth’s Layers Divided in 2 ways Compositional Layers & Mechanical Layers

Compositional Layers Crust: Felsic and mafic rock, 0-65 km Mantle: Liquid and solid rock, km Core: Inner and Outer levels, made of iron and nickel, km

Earthquake Waves Inside the Earth Earthquake wave velocity depends on the type of material and density When waves move from one type of material to another, they change speed and refract

Earthquake Shadow Zone The areas that never receives earthquake waves

Mechanical Layers Divided by how fast P and S waves travel through them Lithosphere: Crust and uppermost part of mantle, P and S waves move through them

Mechanical Layers Aesthenosphere: P and S waves can move through them, but slow down and refract due to material change Mesosphere: Mantle becomes more solid, P and S waves speed up Outer Core: Liquid nickel and iron, P waves slow down, S waves stop Inner Core: Solid iron and nickel, P waves speed up and refract due to state change

Elastic Rebound Theory Friction & stress builds between plates as they try to move past each other

Faults A fault is a break in Earth’s crust along which movement occurs, movement along the faults is what causes earthquakes 1. Strike Slip Fault 2. Oblique Normal Fault 3. Normal Fault 4. Reverse Fault

Example: India As the Indian plate pushed India into the Eurasian plate, faults formed on all sides of the landmasses This created many strike-slip faults, which has led to earthquakes This also made the Himilayas

The Himilayas

Strike-Slip/Transform Fault In this fault, rocks on either side of the fault move past each other The San Andreas fault is an example A B A B

Normal Faults Occur when rocks on one side drop relative to rocks on the other These occur where tension is pulling the crust apart, and the side are diverging AB A B

Reverse Faults This fault occurs when one side of the fault plane is driven up the other side These faults play an important part in mountain building

The Moho In 1909, Andrija Mohorovic noticed an abrupt change in speed of 2 P waves One had sped up faster than the other at a depth of about 32 km This area was named the Moho after him, and it is an area of dense rock that serves as the boundary between the crust and mantle