# Earthquakes: - PowerPoint PPT Presentation

1 / 14

Earthquakes:. How to find where they originate…. Terminology:. Epicenter vs. Focus Focus is the point beneath Earth's surface where rock breaks under stress (or plates shift) and causes an earthquake . Epicenter is the point on land, directly above the focus. Graph vs Gram.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Earthquakes:

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

## Earthquakes:

How to find where they originate…

### Terminology:

• Epicenter vs. Focus

• Focus is the point beneath Earth's surface where rock breaks under stress (or plates shift) and causes an earthquake.

• Epicenter is the point on land, directly above the focus

### Graph vs Gram

• Seismograph are instruments that measure and record motions of the ground, including seismic waves generated by earthquakes, nuclear explosions, and other seismic sources

• Seismogram is a graph output by a seismograph. It is a record of the ground motion at a measuring station as a function of time.

• How Seismograph Works

### S waves vs P waves

• P waves

• Primary Waves

• Named that because they leave the focus first

• Travel faster than S waves

• Compression Waves

• S waves

• Secondary Waves

• Named that because they leave the focus second

• Travel slower than P waves

• Transverse Waves

• S wave P wave Animation

### How do we locate earthquakes?

• Seismograph data (seismograms) will tell us distance from an earthquake epicenter

• We need 3 seismograph readings to find an epicenter

1400 km from Denver, 2600 km from Houston, 4000 km from Miami

### How do we determine distance?

• Lag time between P wave and S wave tells us distance

• Fast Runners and Slow Runners...

### Try the activity:

• http://www.sciencecourseware.com/VirtualEarthquake/VQuakeExecute.html