1 / 29

Chapter 8 Earthquakes

Chapter 8 Earthquakes. San Francisco-1989. 1994- Northridge, CA. Section 8-1. What causes Earthquakes?. Stress of plates moving causes rock to bend and stretch.

ormand
Download Presentation

Chapter 8 Earthquakes

An Image/Link below is provided (as is) to download presentation 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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 8 Earthquakes San Francisco-1989 1994- Northridge, CA

  2. Section 8-1 What causes Earthquakes? Stress of plates moving causes rock to bend and stretch. Rocks reach their elastic limit and break, causing a sudden movement along a fault. During elastic rebound, energy is released. The energy released by the breaking of rock along a fault causes an earthquake

  3. Elastic rebound

  4. Where do Earthquakes occur? • Most occur along plate boundaries. • Along fault systems, some which can be far away from plate boundaries. • Around actively erupting volcanoes.

  5. Earthquakes in Last 30 Days Worldwide

  6. Earthquakes in the last week.

  7. PA eq’s

  8. Types of Faults Normal Fault-tension pulls rocks apart

  9. Fault Video

  10. Reverse Fault-compression pushes rock, one piece is forced up and over another.

  11. Strike-slip Fault-friction from shearing force builds up and rocks move when elastic limit is reached.

  12. Seismic waves

  13. Focus/Epicenter

  14. Types of Seismic Waves Primary (P-waves)- fastest of waves, travel at 6 km per second in an accordion-like motion. Weakest wave Secondary (S-waves)- travel half the speed of P-waves (3 km per second), move in a side to side motion. Stronger than P waves Surface (L-waves)- slowest of waves, move in a wave-like motion, strongest, cause the most destruction in an EQ

  15. Earthquakes are detected by a device called a seismograph Seismograph Seismogram Seismogram- paper record of EQ shaking. • An analysis of a seismogram tells seismologists 2 things: • How powerful the Earthquake is. • How far away the epicenter of the EQ is.

  16. Seismogram

  17. Finding Epicenter • Use P-wave arrival times • Use S-P lag times 3 Times are needed to pinpoint epicenter of EQ

  18. 8-2 EQ Measurement How do seismologists calculate the magnitude of an EQ? Mercalli Scale- old method of measuring EQ’s by damage caused. Not accurate due to building strengths in different areas. Richter Scale- measures EQ’s by describing how much energy is released by the EQ.

  19. How to find Richter Value Scale is from 0.1 to 9+ For every increase of 1.0 on Richter scale, 100 times more energy is released. 6.0 quake is 10,000 times stronger than a 4.0 Amplitude and Distance to find the Richter Value Get info from the seismogram!

  20. Predicting EQ’s Very difficult to predict actual day, more on time span. 1. Creep meter- measures movement by tying a wire across fault to measure movement 2. Lasers- line up laser and mirror on opposite sides of fault 3. Seismic gap- looks for areas that are building up stress along fault. 4. Satellite observations- use of GPS to monitor movement. SMALL MOVEMENT ALONG A FAULT CAN LEAD TO LARGE EARTHQUAKES.

  21. Structures are strongest when they are built on BEDROCK. Soft Earth leads to LIQUEFACTION.

  22. Base Isolators and Cross-bracingbest ways to strengthen buildings

  23. EQ Safety EQ Preparation: What to do during and after EQ:

More Related