Transcript Earthquakes
Earthquakes Chapter 19 What is an earthquake? • Natural vibration of the ground • Caused by movement along fractures or volcanic eruptions 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. 3 Kinds of stress 1. Compression: Pushes together 1. Tension: Pulls apart 1. Shear: Twists Faults • Many rocks that make up the crust fail when stress is applied to quickly. • The result is a system of fractures called FAULTS. Three Types of Faults Seismic Waves • Vibrations of the ground during an earthquake are called Seismic Waves (there are 3 types). 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 http://daphne.meccahosting.com/~a0000e89/insideearth2.htm Secondary Waves (S Waves) • Cause rocks to move at right angles in relation to the direction of the wave. http://daphne.meccahosting.com/~a0000e89/insideearth2.htm Surface Waves • Move in 2 directions as they pass through rock. • Produces motion in the upper crust – Motion can be up and down – Motion can be around – Motion can be back and forth • Travel more slowly than S and P waves • More destructive Focus – point inside the Earth where an earthquake begins Epicenter – point on Earth’s surface above focus Seismology: the study of earthquakes How Seismographs (seismometers) Work the pendulum remains fixed as the ground moves beneath it Typical Seismogram http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt 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 waves • The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves How are Earthquakes Measured? Richter Scale: The size of the largest seismic wave in magnitude. How are Earthquakes Measured? Mercalli Intensity Scale Most earthquakes…. Are associated with tectonic plate boundaries. Almost 80% of all earthquakes occur in the Circum-Pacific Belt! Destruction to buildings Pancaking” “ • Where structural buildings fall and debris resembles a stack of pancakes. Tsunamis http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Formation of a tsunami http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt Tsunami Warning System http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt