Earthquakes
What are earthquakes?
•Vibration in the ground that result frommovement along faults.
•Fault = a break in Earth’s lithosphere whereone block of rock moves toward, away from,or past another.
Why do earthquakes occur?
•Result from the buildup and release of stressalong active plate boundaries.
Where do earthquakes occur?
•The deepest earthquakes occur at convergentplate boundaries where the denser oceanicplate subducts into the mantle(ocean-continent or ocean-ocean boundaries)
•Shallow earthquakes are common alongdivergent and transform plate boundaries.
Most earthquakes occur in oceans and alongedges of continents. Why?
Types of Faults – where earthquakes occur
Seismic Waves
•Energy that travels as vibration on and inEarth as rocks move along a fault.
Epicenter = the locationon the Earth’s surfacedirectly above theearthquake’s focus.
Focus = the location deepinside the Earth where thewaves originate – wherethe rocks first move alongthe fault.
How do scientists classify seismic waves?
Use:
•Wave motion
•Wave speed
•Type of material the waves travel through
3 Types of Seismic Waves
Who studies these waves?
•Seismologists = scientists that studyearthquake waves
•Use these waves to map Earth’s interior
•Also try to predict future earthquakes
How do earthquake waves map Earth’s interior?
P-waves and S-waves at different depths withinEarth’s interior travel at different speeds.
How are these waves measured?
•Seismometer (seismograph)= measures andrecords ground waves and the distance anddirection the seismic waves travel.
•Seismogram = graphical illustration of thewaves.
Triangulation
•The method used to locate an earthquake’sepicenter.
•P. 299 of textbook
•Scientists can use three different scales tomeasure and describe earthquakes.
•The Richter magnitude scale uses theamount of ground motion at a givendistance from an earthquake to determinemagnitude.
•The moment magnitude scale measures thetotal amount of energy released by theearthquake.
Measuring an Earthquake’s Magnitude
The ModifiedMercalli scalemeasures earthquakeintensity based ondescriptions of theearthquake’s effectson people andstructures.
Areas that experienced earthquakes in thepast will likely experience earthquakes again.
•Seismologists assess earthquake risk by studyingpast earthquake activity and local geology.