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1. EarthquakesEarthquakes
By GUlBahar JamaliBy GUlBahar Jamali
Contact:03023076659Contact:03023076659
Univeristy of SindhUniveristy of Sindh
JamshoroJamshoro

2. Global Earthquake LocationsGlobal Earthquake Locations

3. 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 is
maintained without release, the more likely that a strong earthquake will occur.
Types of seismic wavesTypes of seismic waves
1. Body waves -- travel through interior
2. Surface waves -- travel on surface of earth
Specific Body WavesSpecific Body Waves
Primary or "P" Waves: Primary waves Highest velocity
Causes compression and expansion in direction of wave travel.
Secondary or "S" Waves: Secondary or shear waves
Slower than P waves but faster than surface waves.
Causes shearing of rock perpendicular to direction of wave propagation
Cannot travel through liquids
Surface Waves or "Love" (“L”) WavesSurface Waves or "Love" (“L”) Waves
Cause vertical & horizontal shaking
Travel exclusively along surface of earth

4. Primary orPrimary or
“P” Wave“P” Wave
SecondarySecondary
or “S”or “S”
WaveWave

6. Types of SeismographsTypes of Seismographs

8. Seismogram PrintoutSeismogram Printout

9. Determining the location of an earthquakeDetermining the location of an earthquake
First, distance to earthquake is determined.
1. Seismographs record seismic waves
2. From seismograph record called the seismogram, measure time delay
between P & S wave arrival
3. Use travel time curve to determine distance to earthquake as function
of P-S time delay
Now we know distance waves traveled, but we don't know the direction from
which they came.
We must repeat the activity for each of at least three (3) stations to
triangulate a point (epicenter of quake).
Plot a circle around seismograph location; radius of circle is the distance to the
quake.
Quake occurred somewhere along that circle.
Do the same thing for at least 3 seismograph stations; circles intersect at
epicenter. Thus, point is triangulated and epicenter is located.

10. Focus and Epicenter of EarthquakeFocus and Epicenter of Earthquake

11. Time-Travel CurveTime-Travel Curve

12. TriangulationTriangulation
of 3 stationsof 3 stations
to locateto locate
earthquakeearthquake
epicenterepicenter

13. Determining the magnitude of an earthquakeDetermining the magnitude of an earthquake
Magnitude -- measure of energy released during earthquake.
There are several different ways to measure magnitude.
Most common magnitude measure is Richter Magnitude, named for the
renowned 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 greater
magnitude.
• Going up one whole unit on Richter Scale represents about a 30 times
greater release of energy.
IntensityIntensity
• Intensity refers to the amount of damage done in an earthquake
• Mercalli Scale is used to express damage

14. 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 lose
strength by liquefaction.
Buildings respond differently to shaking depending on construction styles,
materials
Wood -- more flexible, holds up well
Earthen 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 below
coastal areas.
If earthquake displaces sea surface, wave is generated that can grow as it
moves over sea surface.
• Fires
Usually occurs from shifting of subsurface utilities (gas lines)

15. Tsunami MovementTsunami Movement

16. 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

17. Earthquake Prediction (?)Earthquake Prediction (?)
How can scientists predict an earthquake?
Currently, that is not possible.
Future technology will monitor subsurface seismic waves and
periodic shifting indicative of future slippage.
Tracking organic movement is also a source of future study.

18. Parkfield, CAParkfield, CA
““Earthquake Capital of the World”Earthquake Capital of the World”
Earthquake Hazard Potential MapEarthquake Hazard Potential Map

19. World’s Largest Earthquake: 1964 Anchorage, AlaskaWorld’s Largest Earthquake: 1964 Anchorage, Alaska
Registered 8.6 on Richter ScaleRegistered 8.6 on Richter Scale

20. Key TerminologyKey Terminology
Seismic waves Body waves
Surface waves Primary (“P) waves
Secondary (“S”) waves Love (“L”) waves
Seismograph Seismogram
Focus Epicenter
Time-travel curve Magnitude
Intensity Richter Scale
Mercalli Scale Logarithmic
Liquefaction Fault scarp
Tsunami Hazard potential map

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