Earth’s Structure:
*6,000 km down to reach the center of the Earth
*It’s NOT just rock
* 4 Layers:
1) crust (solid rock)
2)mantle (solid rock AND soft rock)
3)outer core (liquid iron)
4)inner core (solid iron and nickel)
Earth’s Crust:
*the crust and uppermost part of Earth’s mantle are divided into sections called PLATES
*PLATES: blocks of crust and upper mantle rock that fit together like puzzle pieces
*10 major plates--a) MOST of N. America, Greenland, and part of the Atlantic Ocean are on the NORTH AMERICAN
PLATE
b)Part of California and the Pacific Ocean are on the PACIFIC PLATE
*plates “float” on the softer rock of the mantle
*the movement of plates affects other plates
*plates can move toward each other, away from each other, or alongside each other
Earthquakes:
*when 2 of Earth’s plates move suddenly past each other, energy is released (in the Earth’s crust) and
the ground shakes
*focus: place within the crust where the energy is released during an earthquake
*sometimes this release of energy may hardly be noticed, or it may cause lots of damage
*the GREATEST damage likely occurs directly above the focus---called the epicenter
*caused by 3 different types of plate movement (together, apart, slide past)
* most earthquakes occur along a FAULT---a break in the Earth’s crust
**Some faults occur in the middle of plates, but MOST are found near the edges of plates
*STRONG earthquakes: plates pushing together or sliding past each other
*WEAK earthquakes: plates pulling apart
*Scientists classify earthquakes by measuring their MAGNITUDE---amount of energy released
**this is reported using the Richter scale
2.0 is too small to be felt….6.0 or higher can cause lots of damage
FYI: 1) each increase of 1 on the Richter scale is an increase in strength of about 32 times
2) about 20 earthquakes of magnitude 6.0 or higher occur each year