1. EARTHQUAKES: WHY? AND HOW?

2. EARTHQUAKES Caused by plate tectonic stresses sudden movement or shaking of the Earth Located at plate boundaries Resulting in breakage of the Earth’s brittle crust

3. PLATE TECTONIC STRESSES faults (= cracks where plate sections are moving in different directions)Plate boundaries and faults (= cracks where plate sections are moving in different directions) cause friction as plates move Plates in a fault zone have STICK-SLIP motion –Periods of no movement (stick) and fast movement (slip) –Energy stored as plates stick, –Energy released as plates slip

4. EARTHQUAKE DAMAGE Most caused by SURFACE waves (arrive last)

5. EARTHQUAKE WAVES FOCUS = place deep within the Earth and along the fault where rupture occursFOCUS = place deep within the Earth and along the fault where rupture occurs EPICENTER = geographic point on surface directly above focusEPICENTER = geographic point on surface directly above focus SEISMIC WAVESSEISMIC WAVES produced by the release of energySEISMIC WAVES SEISMIC WAVES –move out in circles from the point of rupture (focus) –2 types: surface & body (travel inside & through earth’s layers) P waves: back and forth movement of rock; travel thru solid, liquid, gas S waves: sideways movement of rock; travel thru solids only

6. Ancient Seismographs Around 132 AD, Chinese scientist Chang Heng invented the first seismoscope, an instrument that could register the occurrence of an earthquake. Seismographs record a zigzag trace that shows the varying amplitude of ground oscillations beneath the instrument. Sensitive seismographs, which greatly magnify these ground motions, can detect strong earthquakes from sources anywhere in the world.

7. Modern Seismographs Sensitive seismographs, which greatly magnify these ground motions, can detect strong earthquakes from sources anywhere in the world.

8. EARTHQUAKE WAVES Seismographs record earthquake waves Seismograms show: Amplitude of seismic waves (how much rock moves or vibrates)Amplitude of seismic waves (how much rock moves or vibrates) Distance to the epicenterDistance to the epicenter Earthquake directionEarthquake direction

9. 3 types of seismic waves show up on seismogram3 types of seismic waves show up on seismogram –P waves: shake earth in same direction as wave; travel thru solid, liquid, gas –S waves: Shake earth sideways to wave direction; travel thru solids only –Surface waves: circular movement of rock; travel on surface – cause most damage!!

10. P-Wave(Body Wave) Primary or compressional (P) waves  The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave.  The P wave can move through solid rock and fluids, like water or the liquid layers of the earth.  It pushes and pulls the rock it moves through just like sound waves push and pull the air.  Highest velocity (6 km/sec in the crust)

11. P-Wave Particle motion Deformation propagates

13. Secondary Wave (S Wave) Secondary or shear (S) waves  The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake.  An S wave is slower than a P wave and can only move through solid rock. (3.6 km/sec in the crust)  This wave moves rock up and down, or side-to-side.

14. S-Wave Particle motion Particle motion consists of alternating transverse motion. Particle motion is perpendicular to the direction of propagation (transverse). Transverse particle motion shown here is vertical but can be in any direction. Material returns to its original shape after wave passes. Deformation propagates

16. EARTHQUAKE WAVES P waves move through solids & liquids S waves move through solids only!!!

17. EARTHQUAKE WAVES Body P wavesS waves waves AKA Moves through Movement of rock Primary (1st to arrive) Longitudinal, Compression all states of matter (solid, liquid, gas) back and forth movement of rock push/pull or compression/stretch out Like slinky down stairs Vibration is same as the direction of travel Secondary (2nd to arrive - larger) Transverse, Shear Can go through solids only Move sideways perpendicular to direction of wave travel Like snake

18. EARTHQUAKE WAVES Lets test your understanding!! Is this a P or an S wave? P wave! S Wave

19. EARTHQUAKE MAGNITUDE measures the size of seismic waves  the energy released by the earthquake measures the size of seismic waves  the energy released by the earthquake Richter scale=measurement of energy released based upon wave amplitude (size of vibration) <2 to ~10<2 to ~10 Amplitude of wave goes up by 10 (Logarithmic scale)Amplitude of wave goes up by 10 (Logarithmic scale) What you need: Amplitude (size of vibration = wave height)Amplitude (size of vibration = wave height) Time between arrival of 1 st P and 1 st S wavesTime between arrival of 1 st P and 1 st S waves

20. HOW TO READ SEISMOGRAMS P & S (body waves) move through earth & arrive first P & S waves used to calculate magnitude of earthquake Amplitude = height of wave (how much the rock moves; size of vibration)

21. Seismic Velocities

22. Why are seismic waves important? Some things seismic waves are good for include · Mapping the Interior of the Earth · Monitoring the Compliance of the Comprehensive Test Ban Treaty · Detection of Contaminated Aquifers · Finding Prospective Oil and Natural Gas Locations

23. IRIS Earth’s Interior Structure Poster – Seismic waves through the Earth

24. Earth’s interior structure and seismic raypaths that are used to determine the Earth structure.