EarthquakesEarthquakesBy GUlBahar JamaliBy GUlBahar JamaliContact:03023076659Contact:03023076659Univeristy of SindhUniveristy of SindhJamshoroJamshoro
Global Earthquake LocationsGlobal Earthquake Locations
EarthquakesEarthquakes • Shaking of earth due to movement of rocks along a fault.• Rocks under stress accumulate strain energy over time.• When stress exceeds strength of rocks, rock breaks.• Strain energy is released as seismic waves. The longer that energy is stored up and ismaintained without release, the more likely that a strong earthquake will occur. Types of seismic wavesTypes of seismic waves1. Body waves -- travel through interior2. Surface waves -- travel on surface of earth Specific Body WavesSpecific Body WavesPrimary or "P" Waves: Primary waves Highest velocityCauses compression and expansion in direction of wave travel.Secondary or "S" Waves: Secondary or shear wavesSlower than P waves but faster than surface waves.Causes shearing of rock perpendicular to direction of wave propagationCannot travel through liquids Surface Waves or "Love" (“L”) WavesSurface Waves or "Love" (“L”) WavesCause vertical & horizontal shakingTravel exclusively along surface of earth
Determining the location of an earthquakeDetermining the location of an earthquakeFirst, distance to earthquake is determined.1. Seismographs record seismic waves2. From seismograph record called the seismogram, measure time delaybetween P & S wave arrival3. Use travel time curve to determine distance to earthquake as functionof P-S time delay Now we know distance waves traveled, but we dont know the direction fromwhich they came.We must repeat the activity for each of at least three (3) stations totriangulate a point (epicenter of quake). Plot a circle around seismograph location; radius of circle is the distance to thequake.Quake occurred somewhere along that circle.Do the same thing for at least 3 seismograph stations; circles intersect atepicenter. Thus, point is triangulated and epicenter is located.
Focus and Epicenter of EarthquakeFocus and Epicenter of Earthquake
Determining the magnitude of an earthquakeDetermining the magnitude of an earthquakeMagnitude -- measure of energy released during earthquake.There are several different ways to measure magnitude.Most common magnitude measure is Richter Magnitude, named for therenowned seismologist, Charles Richter. Richter MagnitudeRichter Magnitude• Measure amplitude of largest S wave on seismograph record.• Take into account distance between seismograph & epicenter. Richter ScaleRichter Scale• Logarithmic numerical (NOT a physical) scale• Increasing one whole unit on Richter Scale represents 10 times greatermagnitude.• Going up one whole unit on Richter Scale represents about a 30 timesgreater release of energy.IntensityIntensity• Intensity refers to the amount of damage done in an earthquake• Mercalli Scale is used to express damage
Hazards associated with QuakesHazards associated with Quakes• Shaking:Frequency of shaking differs for different seismic waves.High frequency body waves shake low buildings more.Low frequency surface waves shake high buildings more.Intensity of shaking also depends on type of subsurface material.Unconsolidated materials amplify shaking more than rocks do.Fine-grained, sensitive materials can lose strength when shaken. They losestrength by liquefaction.Buildings respond differently to shaking depending on construction styles,materialsWood -- more flexible, holds up wellEarthen materials -- very vulnerable to shaking.• Ground displacement:Ground surface may shift during an earthquake (esp. if focus is shallow).Vertical displacements of surface produce fault scarps.• Tsunamis (NOT tidal waves)Tsunamis are huge waves generated by earthquakes undersea or belowcoastal areas.If earthquake displaces sea surface, wave is generated that can grow as itmoves over sea surface.• FiresUsually occurs from shifting of subsurface utilities (gas lines)
Tsunami Movement:Tsunami Movement: ~600 mph in deep water~600 mph in deep water~250 mph in medium depth water~250 mph in medium depth water~35 mph in shallow water~35 mph in shallow water
Earthquake Prediction (?)Earthquake Prediction (?)How can scientists predict an earthquake?Currently, that is not possible.Future technology will monitor subsurface seismic waves andperiodic shifting indicative of future slippage.Tracking organic movement is also a source of future study.
Parkfield, CAParkfield, CA““Earthquake Capital of the World”Earthquake Capital of the World”Earthquake Hazard Potential MapEarthquake Hazard Potential Map
World’s Largest Earthquake: 1964 Anchorage, AlaskaWorld’s Largest Earthquake: 1964 Anchorage, AlaskaRegistered 8.6 on Richter ScaleRegistered 8.6 on Richter Scale