Earthquakes occur most frequently at plate boundaries where plates are separating, colliding, or sliding past one another. They also occur along faults within plates. The type and intensity of quakes depends on the plate boundary type. Divergent boundaries see frequent, mild quakes while convergent boundaries experience more intense quakes as pressure builds over time. Transform boundaries produce less predictable quakes ranging from frequent small ones to rare large ones. Magnitude is used to describe earthquake intensity and is measured using the Richter scale. Tsunamis are generated by undersea earthquakes and send waves of water onto coastlines, traveling great distances in short times.

1. Earthquakes

2. So, what’s the significance of this “special purpose” map?...

3. Earthquakes happen most frequently at plate boundaries or margins Divergent Boundaries o Quakes are frequent and mild because plates separation prevents buildup of pressure o Quakes are shallow because Oceanic crust is thin and is not being pushed into the mantle Convergent Boundaries o More intense because colliding plates build up pressure over time and release it o Quakes are deeper because crust is being pushed into the mantle in subduction process Transform Boundaries o Less predictable o Some plates pass each other smoothly, creating frequent but small quakes o Some plates lock up for long periods, building enormous pressure that is released in more rare but larger quakes

4. Earthquakes also occur along FAULT lines that are not necessarily at plate margins. FAULTS are simply BREAKS in the rocks that are found in the Earth’s crust (continental or oceanic).

5. Photo of an eroded Strike-Slip Fault in California Strike-Slip Faults are also known as TRANSFORM Faults

6. Earthquake Terminology FAULT - break in the rock along which crustal movement takes place FOCUS - the actual spot in the crust where movement originated EPICENTER - the place on the surface directly above the Focus; usually the place most affected by movement SEISMIC WAVES - movement that radiates away from the focus, both within the crust and on the surface

7. Seismograph Earthquake intensity is described as MAGNITUDE

8. An Earthquake’s MAGNITUDE is rated on the RICHTER SCALE

10. TSUNAMIS Waves generated from Earthquakes that occur under the ocean http://www.youtube.com/watch?feature=endscreen&NR=1&v=w3AdFjklR50 The sudden crustal movement sends waves of water in all directions. When the waves move from deeper water to shallower areas near the coastline, large waves build up and crash onto the coastline.

11. TSUNAMIS can travel GREAT distances in relatively SHORT periods of time...

12. ANATOMY of a TSUNAMI TSUNAMIS begin with movement in the crust over a body of water, usually in SUBDUCTION ZONES. http://www.youtube.com/watch?NR=1&feature=endscreen&v=bG37DEAb3Bc The SEISMIC WAVES transfer movement from the crust to the water. http://www.youtube.com/watch?NR=1&feature=endscreen&v=aHljDIDf6js At the EPICENTER, the water movement spreads out in all directions. http://www.youtube.com/watch?v=APDvwlL8jZk&feature=endscreen&NR=1