2 What is an earthquake? Natural vibration of the ground Caused by movement along fractures or volcanic eruptions
3 Most earthquakes occur when… Rocks fracture or break deep within the Earth.Fractures form when STRESS, the forces per unit area acting on a material, exceeds the strength of the rocks involved.
4 3 Kinds of stress Compression: Pushes together Tension: Pulls apart Shear: Twists
5 FaultsMany rocks that make up the crust fail when stress is applied to quickly.The result is a system of fractures called FAULTS.
6 Three Types of Faults Three types of faults Form depending on type of plate motion and complex reaction of earth’s lithospheric blocksStrike-slipNormalThrust
7 Seismic WavesVibrations of the ground during an earthquake are called Seismic Waves (there are 3 types).
8 1. Primary Waves (P Waves) Squeeze and pull rocks in the same direction along the wave direction.The first wave to arrive at an earthquake
9 Secondary Waves (S Waves) Cause rocks to move at right angles in relation to the direction of the wave.
10 Surface Waves Move in 2 directions as they pass through rock. Produces motion in the upper crustMotion can be up and downMotion can be aroundMotion can be back and forthTravel more slowly than S and P wavesMore destructive
11 Focus –. point inside the Earth where an Focus – point inside the Earth where an earthquake begins Epicenter – point on Earth’s surface above focus
15 How do scientists calculate how far a location is from the epicenter of an earthquake? Scientists calculate the difference between arrival times of the P waves and S wavesThe further away an earthquake is, the greater the time between the arrival of the P waves and the S waves
16 How are Earthquakes Measured How are Earthquakes Measured? Richter Scale: The size of the largest seismic wave in magnitude.
17 How are Earthquakes Measured? Mercalli Intensity Scale
18 Most earthquakes…. Are associated with tectonic plate boundaries Most earthquakes…. Are associated with tectonic plate boundaries. Almost 80% of all earthquakes occur in the Circum-Pacific Belt!
19 Destruction to buildings “Pancaking”Where structural buildings fall and debris resembles a stack of pancakes.