Earthquakes Chapter 11

Plate Movements The interactions between plates cause earthquakes and volcanoes.

Earthquakes Vibrations caused by the temporary stopping and then slipping of plates due to built up pressure. May be undetectable or very destructive

Faults Earthquakes occur along faults which are breaks between plates. Rocks along plate boundaries tend to bend, compress or stretch. Faults are formed from: The breaking of rock due to extreme stress/pressure. The elastic limit or breaking point of rock must be reached. Earthquakes occur when the rock breaks along faults.

Fault Types There are three types of faults: Normal fault - one side slips down as the two plates move away from each other. Reverse fault - One side moves up as the two plates move toward each other Strike-slip fault (transform fault) – two plates move horizontal to each other.

Earthquake Waves Earthquakes create waves that travel through the Earth called seismic waves. Seismic waves are produced at one point under the Earth’s surface called a focus.

Seismic Waves Body waves Surface waves - happen at same time Primary waves (P-waves) move in a back and forth motion in the direction of movement. Are the fastest type of wave Secondary waves (S-waves) move at right angles to the direction of movement. Are slower. Surface waves - happen at same time Rayleigh waves (R-waves) move in a backward rolling Love waves (L-waves) a side-to-side motion.

Epicenter Is directly above the focus – on the surface.

Seismographs Seismographs measure the time between and strength of seismic waves of earthquakes. If three or more seismograph stations are affected by an earthquake then an epicenter can be determined.

Measuring earthquakes Richter scale Scales magnitude or energy released (a number 0.1 to 9.5) For every 1.0 increase, ten times as much energy is released. Mercalli scale Scale based on damage (1-12) Descriptions of damage to structures and nature are given for each number.

Earthquake results Liquefaction – is when vibrations cause solid soil to act like a liquid. Earthquakes on the ocean floor produce seismic sea waves called tsunamis.