8th grade Science Study Guide – Earthquakes

 Seismology is the science in which earthquakes are studied.  A seismologist is a scientist that studies earthquakes.  Seismologists use a seismogram to determine when an earthquake started.  The focus is the place within the Earth where an earthquake begins.  The epicenter is the place on the Earth’s surface directly above an earthquake’s starting point.  A seismograph is an instrument located at or near Earth’s surface that records seismic waves.  A seismogram is the tracing of earthquake motion made by a seismograph.  Seismologists use the Richter magnitude scale to measure the strength of an earthquake.  The measure of the strength of an earthquake is called the earthquake’s magnitude.  The degree to which people feel an earthquake and how much damage it causes is called the earthquake’s intensity.  The measurement of how likely an area is to have damaging earthquakes is called earthquake hazard.  The Gap Hypothesis states that active faults with few earthquakes in the past will have strong ones in the future.  If you are indoors when an earthquake strikes you should immediately lie under a table and cover your head.  If you are outdoors when an earthquake strikes you should immediately go to a place away from buildings and trees, lie face down, and cover your head with your hands. Do not run back into your home.  To prepare for an earthquake before it happens, you should safeguard your home, plan a place to meet others, and store food, water, and other useful things.  Convergent boundary = motion that happens when two plates push together.  Transform boundary = motion that happens when two plates slip past each other.  Divergent boundary = motion that happens when two plates pull away from each other.  During elastic rebound, the energy released travels as seismic waves in all directions from the focus.  Rock that deforms like a stretched rubber band is an example of elastic deformation.  A thing that acts like a shock absorber in an earthquake-resistant building is a base isolator.  Flexible pipes are used in earthquake-resistant buildings to help prevent waterlines and gas lines from breaking.  A common way to retrofit an older home is to be sure that it is securely fastened to its foundation.  A mass damper is a weight in the roof of a building that can shift to counteract the movement of the building during an earthquake.  P waves are the fastest waves. They are also known as primary waves.  S waves are slower than P waves. They cannot travel through liquid. They are also known as secondary waves.  P and S waves are body waves. Body waves are waves of energy that travel through the inside of the Earth.  Surface waves are the most destructive seismic waves.  An earthquake with a magnitude of 5.0 is 10 times stronger than an earthquake with a magnitude of 4.0.  The intensity of an earthquake is usually highest at the epicenter.