Earthquakes 10.1 Forces Inside Earth
Causes of Earthquakes • Passing the Elastic Limit Causes Faulting • Earth’s rocks will bend and stretch up to a point • After that point, rocks may break • Faults – area where rocks move when elastic limit is passed • Faults form along plate boundaries • Earthquakes – rock breaking that releases stored energy to produce vibrations • Types of Faults • Normal Faults • Tension forces pull rock apart. • Rock above fault surface moves downward in relation to the rock below the surface.
Reverse Faults • Compression forces push rocks together. • Rock above the fault surface are forced up over the rocks below the fault surface. • Strike-Slip Faults • Shear forces move rocks sideways past each other. • Rocks on either side of the fault are moving past each other without much upward or downward movement. • As forces keep driving the plates to move, energy builds up and rocks reach their elastic limit. • When rocks are stressed past their elastic limit, they may break and an earthquake may result. Pg. 286 1-3
Earthquakes 10.2 Earthquake Information
Types of Seismic Waves • Seismic waves – energy waves made by earthquakes • Earthquake Focus • Focus – the point in Earth’s interior where the energy release occurs • Seismic waves are produced and travel outward • Seismic Waves • Primary waves – waves that cause particles in rocks to move back and forth in the same direction as the wave • Squeeze together and stretch apart as waves move • Secondary Waves – waves that cause particles in rocks to vibrate at right angles to the direction of the waves
Epicenter – point on Earth’s surface directly above an earthquake’s focus • Surface waves – waves that move particles up and down and side to side in a swaying motion. • Surface waves cause most of the damage.
Locating an Epicenter • Waves travel at different speeds; primary – fastest, surface – slowest. • Scientists use the different speeds of seismic waves to find the distance to an earthquake epicenter. • Seismograph Stations • The farther apart the wave arrivals, the farther away the epicenter is. • Epicenter Location • Needs to be recorded by three stations • Circles are drawn with the radius equaling the distance from the earthquake epicenter. • The point where all three intersect is the earthquake epicenter
Mapping Earth’s Interior • At different depths the speed and path of seismic waves change. • Changes mark the boundaries of the different densities of the Earth’s layers. • Structure of the Earth • Inner core – solid dense center, made mostly of iron, with some nickel and smaller amounts of oxygen, silicon, and sulfur. • Outer core – liquid layer made mainly of iron • Mantle – larges layer, made mostly of silicon, oxygen, magnesium, and iron. • Crust – thinnest, outermost layer made of silicon, aluminum, magnesium, and iron.
Moho Discontinuity • Seismic waves speed up when they reach the bottom of the crust • The boundary between the crust and the mantle is called the Moho discontinuity • Plasticlike Layer • Primary and secondary waves slow down • Then seismic waves speed up as they pass through the solid lower mantle • The denser the layer the faster the seismic waves can travel through • Shadow Zone • Area on Earth where no seismic waves are detected • Secondary waves are stopped completely by the liquid outer core • Primary waves are slowed and bent by liquid outer core
Mantle Samples • Volcanic materials are a window to Earth’s interior. • Magma can break off and bring up pieces of mantle as it rises as lava. • Meteorites • Samples of the deep mantle and core have never been collected • Rocky materials of the solar system are through to have formed at the same time • Study meteorites to understand Earth Pg 295 1- 4
Earthquakes 10.3 Destruction by Eathquakes