•Objectives
1. Compare the 3 types of seismicwaves.
2. Discuss the method scientistsuse to pinpoint an Earthquake (EQ).
3. Discuss the method mostcommonly used to measure themagnitude of EQs.
3 major Types of Seismic Waves
•P waves: primary wave.
–Move fastest
–1st to be recorded
–Travels through solids & liquids
•More rigid material. = faster
3 major Types of Seismic Waves
•S waves: secondary waves.
–2nd waves to be recorded
–Only travel trough solids
3 major Types of Seismic Waves
•L waves: surface waves, also called longwaves.
–Converted from P & S waves when theyreach the surface
–Slowest-moving waves
•Last to be recorded
–Cause surface to rise & fall
Comparing Seismic Waves
Primary Waves (P)
Secondary Waves (S)
Long or Surface Waves(L)
Arrives first
Moves fasterthrough morerigid material
Moves theground togetherand apart alongthe direction ofwaves.
Arrive seconds
About 1.7 timesslower than thePrimary waves
Moves fasterthrough morerigid material
Moves theground at rightangles to thedirection in whichthe waves aretraveling
Arrives last
Slowest of thethree
Travels over theearths surface
Moves theground like theocean waves
Can cause greatdamages whentraveling throughloose earth
Recording EQs
•Seismograph: instrument used todetect and record seismic waves.
Determines the distance and not thedirection of the epicenter.
Distance-Determined by seismograph-
scientists analyze the differencebetween the arrival times of the P andthe S waves.
Locating the epicenter-At least 3seismograph is needed to locate theepicenter.
The method is called Triangulation.
Two recording N.S and E.W vibrationsTwo recording N.S and E.W vibrations
One recording vertical vibrationsOne recording vertical vibrations
Locating an EQ
•Scientists compare time diff. btwnP & S waves.
–Plot on graph to get distance to epicenter
EX: 3 seismographs at locationsA, B, and C, determined thedistance of each point from theepicenter.
Point A (seismograph 1)is 500 km,point B (seismograph 2) is 800 kmand point C is 1200 km (seismograph 3) away from theepicenter. Locate the epicenter.
Locating an EQ
•Need 3 plots to locate epicenter
–Point where all 3 circles meet is location ofepicenter
Richter Scale
Mercalli Scale
Measures the magnitude orthe energy released by anearthquake.
Scale of 1 to 10
Each level releases 31.7times more energy than thatof the lower level
Largest registered, 9.5Richter, Chile 1960.
Strong-7 or above
Moderate 6-7
Minor-2.5-6
Microquakes-2.5 or less. Cannot be felt by people
Expresses the intensity orthe amount of damage itcauses.
Shown by Romannumerals from I to XII.
I-II- Low intensity,little damage
Up to X- Higherintensity, well builtstructures destroyed.
XII- total destruction
EARTHQUAKE DAMAGE
Movement of the ground itself seldomcauses many deaths or injuries.
Most injuries result from the collapse ofthe buildings, flying glass and fallingobjects.
Flood
Fire
Landslide
Damages
•Most buildings are not designed towithstand the swaying motion caused byearthquakes.
•Buildings may collapse, sway violently, or tipover to the neighboring structure.
•Tall buildings should be built on soil or rockthat is firm. Loose soil and rock can vibratelike jelly.
Faulting and under water landslides cancause tsunamis.Tsunamis can cause massive death anddamages.
SSWWS:
Seismic Sea Wave Warning System: Seismicnetwork around the Pacific Ocean.Allows scientist to estimate the arrival times ofthe tsunamis at different locations.