EARTHQUAKES

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EARTHQUAKES

• CHAPTER 10

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HOW AND WHERE EARTHQUAKES OCCUR

• WHAT IS AN EARTHQUAKE?
• A SHAKING OF EARTHS CRUST CAUSED BY A RELEASE OF
  ENERGY
• FROM AN ERUPTION OF A VOLCANO
• THE COLLAPSE OF A CAVE, OR IMPACT OF A METEOR
• WHERE DO THEY OCCUR?
• MOST OCCUR ALONG FAULTS AT OR NEAR PLATE
  BOUNDARIES

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VOCABULARY OF EARTHQUAKES

• FAULT
• BREAK IN THE LITHOSPHERE WHERE MOVEMENT HAS
  OCCURRED
• FOCUS
• THE POINT WHERE THE FIRST MOVEMENT OCCURS
• EPICENTER
• THE POINT ON THE EARTHS SURFACE DIRECTLY ABOVE
  THE FOCUS

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VOCABULARY OF EARTHQUAKES

• BODY WAVES
• WAVES THAT TRAVEL FROM THE FOCUS OF AN EARTHQUAKE
  THROUGH EARTH
• P WAVES
• PRIMARY, COMPRESSIONAL WAVES THAT CAN TRAVEL
  THROUGH SOLIDS AND LIQUIDS
• S WAVES
• SECONDARY, SHEAR WAVES, MOVE IN RIGHT ANGLES TO
  THE DIRECTION IN WHICH THEY ARE TRAVELING,
  THROUGH SOLIDS ONLY

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ELASTIC REBOUND THEORY

• FRICTION PREVENTS THE PLATES FROM MOVING UNTIL
  THE STRAIN BUILDS UP SO MUCH CAUSING THE PLATE
  BOUNDARIES TO DEFORM
• EVENTUALLY THE STRAIN IS TOO MUCH AND FRICTION IS
  OVERCOME
• THE PLATES MOVE SUDDENLY IN A REBOUND EFFECT TO A
  DIFFERENT LOCATION

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EARTHQUAKES

• DEPTH OF THE EARTHQUAKE DEPENDS ON THE PLATE
  BOUNDARY
• DIVERGENT OCCUR WITHIN 30KM OF THE SURFACE
• TRANSFORM CLOSER TO THE SURFACE THAN DIVERGENT
• SUBDUCTION VERY DEEP, AS FAR AS 700KM BELOW
  SURFACE
• DEPTH EFFECTS THE AMOUNT OF DAMAGE ON THE SURFACE

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EARTHQUAKE WAVES

• http//www.matter.org.uk/Schools/Content/Seismolog
  y/pandswaves.html
• WAVES P WAVES OR COMPRESSIONAL WAVES SQUEEZE
  AND STRETCH ROCK MATERIALS AS THEY PASS THROUGH
• S WAVES MAKE THE ROCK MATERIAL MOVE IN AN UP AND
  DOWN MOTION

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MOVEMENT OF WAVES

• THE RATE AT WHICH THE WAVES MOVES DEPENDS ON THE
  MATERIAL THEY ARE MOVING THROUGH
• THE MORE DENSE THE MATERIAL THE FASTER THE WAVES
  TRAVEL
• S WAVES TRAVEL AT ABOUT HALF THE SPEED OF P WAVES
  THROUGH SOLID MATERIAL

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OTHER WAVES

• SURFACE WAVES TRAVEL ALONG THE SURFACE OF THE
  EARTH
• S AND P WAVES PRODUCE SURFACE WAVES WHEN THEY
  REACH THE SURFACE
• TWO TYPES
• 1. LOVE WAVES
• 2. RAYLEIGH WAVES

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OTHER WAVES

• LOVE WAVES CAUSE PARTICLES TO MOVE FROM SIDE TO
  SIDE IN A DIRECTION PERPENDICULAR TO THE WAVES
  DIRECTION
• RAYLEIGH WAVES TRAVEL MORE SLOWLY AND CAUSE
  PARTICLES TO MOVE IN ELLIPTICAL PATTERNS
• SURFACE WAVES TRAVEL MORE SLOWLY THAN P OR S WAVES

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LOCATING AND MEASURING EARTHQUAKES

• SIESMOGRAPH
• INSTRUMENT THAT DETECTS AND RECORDS WAVES
  PRODUCED BY EARTHQUAKES
• USED TO LOCATE AND MEASURE THE MAGNITUDE OF THE
  EARTHQUAKE
• SEISMOGRAM THE PAPER THAT IS PLACED ON THE
  SIESMOGRAPH DRUM AND RECORDS THE WAVES

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• http//www.thetech.org/exhibits/online/quakes/seis
  mo/
• http//www.thetech.org/exhibits/online/quakes/gram
  s/

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INTERPRETING A SEISMOGRAM

• P WAVES TRAVEL FASTER THAN S WAVES AND HIT THE
  SEISMOGRAPH FIRST
• THE FURTHER APART THE P AND S WAVES ARRIVE AT THE
  SEISMOGRAPH THE FURTHER AWAY THE EARTHQUAKE
  EPICENTER IS

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LOCATING AN EPICENTER

• NEED DATA FROM AT LEAST 3 DIFFERENT SEISMIC
  STATIONS
• DRAW A RADIUS FROM THOSE 3 PIECES OF DATA
• WHERE THE CIRCLES ALL INTERSECT IS THE LOCATION
  OF THE EPICENTER

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MAGNITUDE

• THE STRENGTH OF THE EARTHQUAKE IS MEASURED IN
  MAGNITUDE
• DEVELOPED BY CHARLES F. RICHTER
• RICHTER SCALE
• EACH LEVEL IS 31 TIMES MORE POWERFUL THAN THE
  PREVIOUS

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MAGNITUDE

• THE RICHTER SCALE HAS LIMITATIONS
• IT DOES NOT ACCURATELY INDICATE THE AMOUNTS OF
  ENERGY RELEASED IN VERY LARGE EARTHQUAKES
• MOMENT MAGNITUDEMEASURES AMOUNTS OF ENERGY
  RELEASED BY AN EARTHQUAKE

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EARTHQUAKE HAZARDS

• LIQUEFACTION OCCURS WHEN LOOSE SOIL TEMPORARILY
  TAKES ON SOME OF THE PROPERTIES OF LIQUID
• AFTERSHOCKS SMALLER EARTHQUAKES THAT OCCUR
  AROUND THE SAME AREA AFTER A LARGE EVENT
• TSUNAMI CAUSED BY UNDERWATER EARTHQUAKES AND
  LANDSLIDES
• SEISMIC GAP AREAS ALONG A FAULT THAT HAVENT
  MOVED OVER A PERIOD OF TIME THESE ARE AREAS
  THAT MAY BECOME EARTHQUAKES

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EARTHS INTERIOR

• BY STUDYING EARTHQUAKES SCIENTISTS HAVE LEARNED
  ABOUT THE STRUCTURE OF THE EARTH
• KNOWLEDGE OF HOW P AND S WAVES TRAVEL HAVE HELPED
  SCIENTIST DETERMINE THE CHARACTERISTICS OF THE
  EARTHS INTERIOR LAYERS

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SHADOW ZONE

• EARTHQUAKE WAVES TRAVEL IN ALL DIRECTIONS FROM
  THE FOCUS
• THE SHADOW ZONE IS AN AREA ON THE EARTHS SURFACE
  THAT CANNOT DETECT EARTHQUAKE WAVES BECAUSE IT IS
  ON THE OPPOSITE SIDE OF THE EARTH
• THE ZONE EXISTS BECAUSE THE WAVES ARE REFRACTED
  BY THE CORE OF THE EARTH

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THE MOHO

• MOHO THE BOUNDARY WHERE THE DENSE ROCK OF THE
  MANTLE MEETS THE LESS DENSE ROCK OF THE CRUST
• THIS WAS DISCOVERED BY ANDRIJA MOHOROVICIC IN
  1909 (A CROATION SCIENTIST)
• NOTICED AN ABRUPT CHANGE IN THE VELOCITIES OF P
  AND S WAVES AT THIS POINT ON THE EARTH

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TRANSITION ZONE

• DETECTING AN ABRUPT CHANGE IN THE VELOCITY OF THE
  P AND S WAVES AT DEPTHS OF 400 AND 670KM
• THESE MARK REGIONS IN THE EARTHS MANTLE WHERE
  THE TYPE OF MATERIAL CHANGES
• GETS MORE DENSE THE DEEPER YOU GO BECAUSE OF
  INCREASED PRESSURE AND COMPRESSION OF THE MATERIAL