Earthquakes
Earthquakes are movements in the Earth's crust. Most earthquakes take place near or on tectonic plate boundaries adn some of them have faults along them. Earthquakes are caused from deformation. There are two types of deformation but only one, elastic deformation, leads to earthquakes. Elastic deformation is when the rock keeps on stretching and stretching then finally just breaks, and all of the pieces return to their non-stretched shape. With different types of faults means that there are going to be different motions. For instance, if there was a strike-slip fault the motion would be transform. If the plate motion was convergent then the fault would be a reverse fault. Last, a normal fault would have a divergent motion. Scientist use seismographs, an instrument that records vibrations in the ground and determines the location and strength of an earthquake. Seismograms are the tracings of the earthquake motion, that is created by a seismograph. The epicenter of an earthquake is the point directly above the focus. The focus is the starting point of an earthquake, or is the point along a fault where an earthquakes first motion occurs. To find the epicenter scientist use the s-p time method. The Richter Magnitude Scale measures the strength of an earthquake, and the seismologist Charles Richter created this scale in the 1930's. The Modified Intensity Scale measures the intensity of an earthquake and uses Roman numerals to describe the intensity levels.
(Information from: holt Science and Technology book. Pictures from: http://www.docstoc.com/docs/80153368/Modified-Mercalli-Scale-vs-Richter-Scale and http://solarroadways.com/faq.shtml)
(Information from: holt Science and Technology book. Pictures from: http://www.docstoc.com/docs/80153368/Modified-Mercalli-Scale-vs-Richter-Scale and http://solarroadways.com/faq.shtml)