EarthquakesEarthquakes
What’s an Earthquake?What’s an Earthquake?
Earthquakes are movements of the groundthat are caused by a sudden release ofenergy when along a fault move.Earthquakes are movements of the groundthat are caused by a sudden release ofenergy when along a fault move.
Occur when rocks under stress shiftsuddenly along a fault.Occur when rocks under stress shiftsuddenly along a fault.
Stress is a force that can change the size& shape of rocks.Stress is a force that can change the size& shape of rocks.
Elastic Rebound TheoryElastic Rebound Theory
This theory states --- sudden return of elasticallydeformed rock to its undeformed shape.This theory states --- sudden return of elasticallydeformed rock to its undeformed shape.
If the fault is locked, stress increases.If the fault is locked, stress increases.
When stress reaches passed a certain point, therocks fracture, separate at weakest point, andspring back or rebound, to original shape.When stress reaches passed a certain point, therocks fracture, separate at weakest point, andspring back or rebound, to original shape.
As they fracture and slip the rocks along thefault release energy in the form of anearthquake.As they fracture and slip the rocks along thefault release energy in the form of anearthquake.
Anatomy of an EarthquakeAnatomy of an Earthquake
Hypocenter (Focus) – The area along thefault where slippage first occurs.Hypocenter (Focus) – The area along thefault where slippage first occurs.
Epicenter – The point on the Earth’ssurface directly above the focus.Epicenter – The point on the Earth’ssurface directly above the focus.
Anatomy of an EarthquakeAnatomy of an Earthquake
A seismic wave is an elastic wavegenerated by an impulse such as anearthquake or an explosion. Seismicwaves may travel either along or near theearth's surfaceA seismic wave is an elastic wavegenerated by an impulse such as anearthquake or an explosion. Seismicwaves may travel either along or near theearth's surface
2 main types of seismic waves:2 main types of seismic waves:
Body waves – a seismic wave that movesthrough the interior of the earth.Body waves – a seismic wave that movesthrough the interior of the earth.
Surface waves – a seismic wave that travelsnear the earth's surface.Surface waves – a seismic wave that travelsnear the earth's surface.
Types of Body WavesTypes of Body Waves
1.A P wave, orcompressional wave, is aseismic body wave thatshakes the ground backand forth in the samedirection and the oppositedirection as the directionthe wave is moving.1.A P wave, orcompressional wave, is aseismic body wave thatshakes the ground backand forth in the samedirection and the oppositedirection as the directionthe wave is moving.
2.An S wave, or shearwave, is a seismic bodywave that shakes theground back and forthperpendicular to thedirection the wave ismoving.2.An S wave, or shearwave, is a seismic bodywave that shakes theground back and forthperpendicular to thedirection the wave ismoving.
2 Types of Surface Waves2 Types of Surface Waves
1.Surface waves orLove waves or Lwaves – cause rockto move side toside &Perpendicular todirection waves aretraveling.1.Surface waves orLove waves or Lwaves – cause rockto move side toside &Perpendicular todirection waves aretraveling.
2.Rayleigh waves --cause the groundto move with anelliptical, rollingmotion.2.Rayleigh waves --cause the groundto move with anelliptical, rollingmotion.
Major Earthquake ZonesMajor Earthquake Zones
Most earthquakes occur along or near edges ofthe earth’s lithospheric platesMost earthquakes occur along or near edges ofthe earth’s lithospheric plates
Stress is greatest along these moving plateboundaries.Stress is greatest along these moving plateboundaries.
Earth has 3 major earthquake zones:Earth has 3 major earthquake zones:
1.Convergent Oceanic environments – move toward eachother and collide; as the plates move, the overridingplate scrapes across the top of the subducting plate.1.Convergent Oceanic environments – move toward eachother and collide; as the plates move, the overridingplate scrapes across the top of the subducting plate.
2.Divergent Oceanic environments – Make up the mid-ocean ridges, plates are moving away from each other.Spreading causes earthquakes.2.Divergent Oceanic environments – Make up the mid-ocean ridges, plates are moving away from each other.Spreading causes earthquakes.
3.Continental environments – 2 continental platesconverge, diverge, or move horizontally in oppositedirections.3.Continental environments – 2 continental platesconverge, diverge, or move horizontally in oppositedirections.
Fault zones --- Form at plate boundaries because ofintense stress that results when plates separate,collide, subduct, or slide past each other.
Recording EarthquakesRecording Earthquakes
Seismograph – records & detects vibrations inthe ground.Seismograph – records & detects vibrations inthe ground.
Consists of 3 separate devices:Consists of 3 separate devices:
1.One device records the vertical motion of theground.1.One device records the vertical motion of theground.
2.The other 2 devices record horizontal motion in theeast-west and north-south.2.The other 2 devices record horizontal motion in theeast-west and north-south.
The seismograph records motion by tracingwave-shaped lines on paper and translatingthe motion into electronic signals (known as aseismogram).The seismograph records motion by tracingwave-shaped lines on paper and translatingthe motion into electronic signals (known as aseismogram).
Measuring an EarthquakeMeasuring an Earthquake
Richter scale – measures the ground motionfrom an earthquake to find its strength.Richter scale – measures the ground motionfrom an earthquake to find its strength.
Moment magnitude is a measurement of aquakes strength based on size of area the faultmoves, the average distance that the faultblocks move, and the rigidity of the rocks in thefault zone.Moment magnitude is a measurement of aquakes strength based on size of area the faultmoves, the average distance that the faultblocks move, and the rigidity of the rocks in thefault zone.
Mercalli scale – expresses the intensity of anearthquake or the amount of damage it causes.Expressed by a roman numeral and adescription.Mercalli scale – expresses the intensity of anearthquake or the amount of damage it causes.Expressed by a roman numeral and adescription.