Earthquakes!

How does an earthquakes form?  Forces inside the earth put stress on the rocks near plate edges. Stress cause rocks to bend and stretch  Rocks bent past their elastic limit = rock break and move along surfaces called faults  Friction within the faults cause the release of energy making an earthquake

Three types of forces that create faults  Tension: pull apart  Compression: push together  Shear: slide past

Normal Fault  Tension forces pull rock apart  A rock above the fault surface moves downward in relation to rock below the fault surface

Reverse Faults  Compression forces squeeze rock  Rock above a reverse fault surface is forced up and over the rock below the fault surface

Strike-Slip faults  Shear forces move rocks past each other without much vertical movement

Seismic Waves General Info  Seismic waves are the waves of energy released when rocks break along faults.  Focus = the point within the Earth’s Interior at which this energy is first released.  Seismic waves are produced and travel outward from the earthquake focus.  Are Seismic Waves Compressional or Transverse Waves? – Why??

Epicenter  EQ Epicenter = the point on the Earth’s surface directly above the earthquake’s focus.  The speeds of seismic waves allows us to determine how far away earthquake epicenter is from a seismic station.  Measured with Seismograph.

“Body” Waves 1) P-waves (Primary Waves)  Cause particles in rocks to move back & forth in same direction (Compressional) fastest 2) S-waves (Secondary Waves)  Cause particles in rocks to move at right angles to the direction of the wave travel (Transverse Wave.) slower

Surface Waves  Move rock particles in a rolling, side-to-side, swaying motion.  Most damaging type of seismic waves and the Slowest

Measuring EQ’s  Richter Scale Used to measure the strength of an earthquake. Used to measure the strength of an earthquake. Based on the height of the lines on the seismograph. Based on the height of the lines on the seismograph. Scale has no upper limit, but 9.5 is estimated maximum. Scale has no upper limit, but 9.5 is estimated maximum.

Measuring EQ’s  Mercalli Intensity Scale Used to measure the intensity of an earthquake based on the amount of damage caused by the earthquake. Used to measure the intensity of an earthquake based on the amount of damage caused by the earthquake. Scale has 12 levels. Scale has 12 levels.

Earth layers  Inner core: solid. Made of iron  Outer core: liquid. Made of iron  Mantel: liquid magma. Made of Silicon, Oxygen, Magnesium Asthenosphere: upper part of the mantel Asthenosphere: upper part of the mantel  Lithosphere/crust: Solid. Made of Silicon and Aluminum

How do scientist know this?  Seismic wave change pathway and speed at different densities  S-wave stop at the liquid outer core  P-wave are bent and slowed at liquid outer core and then speed up again in solid inner core  PG136

Tsunami  When an earthquake occurs under water the energy released can generate a large wave that can reach 30 m high