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Section 6.1 Objectives 1. Discuss the elastic rebound theory.

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Presentation on theme: "Section 6.1 Objectives 1. Discuss the elastic rebound theory."— Presentation transcript:

1 Section 6.1 Objectives 1. Discuss the elastic rebound theory.
2. Explain why earthquakes generally occur at plate boundaries.

2 Earthquakes & Plate Tectonics
Earthquakes (EQs): vibrations of the Earth’s crust Occur when rocks under stress suddenly shift

3 Elastic Rebound Theory: the theory geologists use to explain many EQs
Rocks on each side of fault are moving If fault is locked, stress increases At certain point rocks fracture & rebound

4 Focus: the area along a fault where slippage 1st occurs.
Depths vary

5 Epicenter: the point on the Earth’s surface directly above the focus.

6 Aftershocks: series of smaller tremors.
Caused by released energy (seismic waves) Increases stress in other rocks along the fault

7 Focus depths vary Shallow focus - w/in 70 km of surface
Tend to cause the most damage

8 Focus depths vary Intermediate focus - 70 to 300 km

9 Focus depths vary Deep focus (occur in subduction zone) 300 to 650 km

10 Focus depths vary About 90% of Continental EQs are shallow focus

11 3 Major EQ Zones Links btwn EQs & Plate Tectonics
Plate movements = stress buildup

12 Pacific Ring of Fire: ring of tectonic/volcanic activity surrounding the pacific.

13 Mid-ocean ridges: spreading motion = stress

14 Eurasian-Melanesian mountain belt: Eurasian plate colliding w/African & Indian plates = stress

15 Fault Zones: are groups of interconnected faults.
Form at plate boundaries b/c of intense stress e.g. San Andreas fault

16 Not all EQs occur at plate boundaries!
e.g. New Madrid, Missouri, 1812 Ancient fault? (600 million yrs ago)


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