Earthquake Lecture Loma Prieta Earthquake in 1989 Bay Bridge collapse in 2009

Earthquakes Result From Stress Inside Earth What is an Earthquake? a. Earthquake (Def) - Shaking of Earth’s crust when energy is released. It snaps like a tired, old schoolteacher!

Stress and Strain Earthquake happen when rocks break (fracture). Stress is the forces placed on rocks. Tensional stress pulls the rocks apart. Compressional stress pushes them together. Shear stress twists and contorts rocks in opposite motions.

Types of Earthquake Faults There are three basic types of faults 1. Reverse Faults 2. Normal Faults 3. Strike-slip Faults

Normal Faults Normal Faults form as a results of horizontal tensional forces The crust is extended and pulled. Footwall is higher Example: Lake Tahoe formed through normal faulting Often occur at divergent boundaries

Reverse Faults (also known as Thrust Faults) Form as a result of compressional forces The hanging wall is higher Often occur at convergent boundaries

Example of a reverse Faults – One rock layer pushed over another rock layer (high angle). Reverse faults are steep!

Strike-Slip Fault Strike Slip are formed as a result of shearing forces Movement along strike slip faults are mostly horizontal San Andreas Fault Often occur at Transform boundaries

Earthquake Focus and Epicenter The Focus is the point where the earthquake originates! The focus is always beneath the Earth’s surface. Earthquakes can be shallow or deep. The epicenter is on the Earth’s surface directly above the focus

Deep and Shallow Earthquakes Deep earthquakes occur in subduction zones Trenches are deeper than Mt. Everest is high!

Seismic Waves P-Waves – Primary waves. Remember particles move parallel to direction of wave motion. Compression & rarefactions! 2) S- Waves - Secondary (shear) waves don’t travel through liquids! Particle motion is perpendicular to wave direction of travel. Transverse waves. 3) Surface Waves (also called L-waves)– Circular waves travel along Earth surface. Destroys buildings.

Clues to Earth’s Interior using Seismic Waves S-waves travel through solids only so when they hit the liquid core, they are deflected. Shows us the outer core is liquid. P waves speed up when they hit the inner core which supports the idea that the inner core is solid

Locating and Measuring Earthquakes 1.Seismographs – Recording instruments. a. Seismogram – Sheets of paper quakes are recorded on. 2. Distance to the Epicenter – Receiver stations around the world help us triangulate & find epicenters.

Travel-Time Graphs and Locating Epicenters The epicenter can be determined with the seismic data from three stations. Data from one station gives distance from the epicenter but not exact location.

Measuring Earthquakes Magnitude – Size of earthquakes Richter Scale – Logarithmic scale of energy released. Scale of 1-10 (though 10 has never happened) Damage Mercalli Scale – Based on observers’ assessment of the Earthquake damage (I-XII)

Some Famous Earthquakes To see the biggest quake in 100 years, go here: http://science.nasa.gov/headlines/y2005/10jan_earthquake.htm?friend

Tsunamis – Giant water waves generated by earthquake energy. Photo taken seconds before this man got swept away!

Tsunamis – Giant water waves Tsunamis – Giant water waves. This picture was taken from a hotel room right before the tsunami hit in Indonesia.