Earthquakes

Remember… Continental drift Plate tectonics Which movement causes earthquakes?

Earthquakes Shaking and trembling of the earth’s crust. About 8000 occur every day or one every 11 seconds Caused by plates sliding beside each other (sliding/transform) Tsunami - earthquake on the ocean floor: causing waves to become greater than 20 meters high

Faults Faults are weaknesses in the rock and therefore earthquakes tend to happen over and over along the same faults.

Most major faults in the United States, particularly in California, are what are known as strike-slip faults. A strike-slip fault is formed where two parts of the earth’s crust (plates) slide past each other.

Thrust Fault A thrust fault occurs when the plate moves in an upward motion.

Normal Fault Normal plate movement is slipping in a downward motion.

Seismic Waves The three main types of seismic waves are: P waves, S waves, and L waves

Seismic Waves …are waves of energy that travel through the Earth as a result of an earthquake

P Waves Primary waves Fastest waves Arrive first at the epicenter

S Waves Secondary waves Move in up-down motion (think of holding one end of a rope and shaking it up and down)

L Waves Slowest moving seismic waves Travel on top of Earth’s surface

Measuring Earthquakes Seismograph-measures and detects seismic waves Richter Scale- a scale that allows scientists to determine earthquake strength 1-10 levels at which an earthquake is measured. Above a 6 is very destructive

Measuring Earthquakes Epicentre: the point on the Earth's surface that is directly above the centre of the earthquake Most violent shaking happens at the epicenter

WHAT INFLUENCES THE AMOUNT OF DAMAGE AN EARTHQUAKE CAUSES? - Magnitude of the earthquake (how it is) - Distance of location from epicentre of the earthquake - Type of movement of the plates or along fault - Soil conditions (loose, solid, flexible, stiff) - Construction type and quality of buildings