# How often do earthquakes occur?

## Presentation on theme: "How often do earthquakes occur?"— Presentation transcript:

How often do earthquakes occur?
Once a year Once a month Once a week Once a day

Earthquakes Seismology  Seismologist  Fault  Deformation 
Elastic rebound  study of earthquakes scientist who studies earthquakes and seismic waves a break in the crust along which plates shift and slip past each other rocks changing shape due to stress from tectonic motion stress builds up to the point where the rock breaks and snaps back

Epicenter – the point on the Earth’s surface directly above an Earthquake’s starting point
Focus – the point inside the Earth where the earthquake begins

Seismic Waves  vibrations that are generated by the earthquake and travel through the Earth
P-waves S-waves L-waves Full name Where they travel Relative speed Type of motion pressure waves (primary) shear waves (secondary) Surface through the entire earth only through solid on the earth’s surface slowest, but most damaging fastest slower up & down, and side to side (circle) back and forth up and down

Surface wave

Seismic Wave Motion with Surface Effects
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Seismic Wave Motion To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Measuring Seismic Waves
Seismograph – Instrument that record waves Seismogram – Printout of waves created by seismograph

Seismographs To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Predicting Earthquakes (SCEC)
Italian Seismologists:

Earthquake Strength and Intensity
What is the measure of the strength of an earthquake called? Magnitude measures the strength of the ground motion Richter scale  Based on a factor of _____ for each level. A magnitude 3 is ____ times as strong as a magnitude 2. A magnitude 4 is ____ times as strong as a magnitude 3. A magnitude 4 is _____ times as strong as a magnitude 2. 10 10 10 100 Historic Earthquakes Chile May 22 19:11:14 UTC Magnitude 9.5 The Largest Earthquake in the World

Mercalli Scale Measures Intensity – how much it is felt by people and how much damage it causes Not as scientific because not based on seisomogram recordings but on peoples’ observations areas closer to epicenter will have higher intensity damage depends on quality of construction

S Waves Arrive P Waves Arrive

Identify the Richter Scale Magnitude of the earthquake
Las Vegas Seismic Station What is the S-P lag time? What is the distance to the earthquake epicenter? What is the S-wave amplitude? What is the magnitude using the nonogram?

AN earthquake with a magnitude of 5
AN earthquake with a magnitude of 5.0 on the Richter Scale will produce 10 times more ground motion as an earthquake with a magnitude of 4.0. How much more ground motion would an earthquake with a magnitude of 7.0 produce compared to an earthquake with a magnitude of 4.0? Answer – 1,000 times more!!