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Earth Shattering POWERPOINT 1 What is an earthquake? • A sudden movement of the earth's crust caused by the release of stress accumulated along plate boundaries or by volcanic activity. 2 How does an Earthquake occur? • • • Rock remains locked until the strain becomes so great the rock suddenly breaks and slips past each other. When rocks break, it releases energy (seismic waves) Called Elastic Rebound theory 3 Elastic Rebound Theory • As tectonic plates are slowly moving, their edges are locked in place, causing bending of the crust along plate boundaries. The original position before any change has occurred. As plates slide past eachother, the rock bends and folds 4 Elastic Rebound Theory • When the force trying to make the edges slip overcomes the friction making them stick, there is an earthquake. • The bending and “springing back” of the rock is called elastic rebound. • Elastic Rebound Animation- Click HERE Rock breaks and releases energy. The rock rebounds (springs) back to its undeformed shape. 5 Images of elastic rebound 6 7 8 Earth Sci rocks 9 • Pretty sure they didn’t build the fence like this! 10 Seismic Waves • Energy waves caused by the release of pressure caused by the movement of tectonic plates. 11 Seismic Waves • There are 2 divisions of seismic waves 1. Those that travel through the Earth (Body Waves) 2. And those that ONLY travel on the crust (Surface Waves) 12 Body Waves • Body waves can travel in the interior of the Earth. • There are TWO Body Waves: – Primary Wave, or P-wave, travels the fastest 9km/second or 5.5mi/second – Secondary Wave, or S-wave, travels a little slower. 6km/sec or 3.5mi/sec 13 P-waves • Can travel through the entire Earth. Through liquids (outer core) and solids (inner core). • The type of wave is called compression. It compresses (squeezes) the matter it’s moving through. (*** your chem teacher might call it longitudinal) • Click HERE for P-waves animation 14 S-waves • S-waves can travel only through the SOLID portion of the interior of the Earth. • They cannot travel through liquids, so they cannot travel through the outer core. • The wave is called a shear wave. Matter is moved perpendicular to motion of energy. (*** Your chem teacher would call this a transverse wave). • Click HERE for animation of S-waves 15 Surface Waves (also called L-waves) • Move much slower than the body wave- roughly speed of sound. Only 1 mile in 5 seconds (or about 700 mi/hr) • Can only travel through the crust of the Earth (surface). • These waves have the biggest amplitude (height of the wave). As a result they do the MOST damage on the surface. • Click HERE for animation- scroll down to the bottom and look at Rayleigh surface wave. 16 How are Earthquakes USEFUL? • • Seismic waves allow us to find the epicenter (location) of an EQ. Seismic waves help us determine the interior of the Earth. 17 How do seismic waves help us find the Earthquake? • Because the P wave and S wave travel at a constant speed, we can determine the distance of an earthquake from a seismic station. 18 How do Seismic waves help us determine the interior of the Earth? • P waves can travel through the entire Earth. • S waves can only travel through the crust and mantle. • This causes seismic wave “shadows” • Click HERE for an animation of seismic waves traveling through the Earth. 19 How do we measure the strength of an Earthquake? • • Richter Scale used to rate the magnitude of an earthquake the amount of energy it released. It is a logarithmic scale, meaning that whole-number jumps indicate a tenfold increase. • – – Richter scale??? Example: Magnitude 5 EQ is 10 times stronger than a magnitude 4 EQ (10 times the ground motion!!!) Magnitude 6 EQ is 10 x 10 (or 100) times stronger (100 times the ground motion) 20