Earthquakes
...the fault, meaning the rocks move past each other horizontally causing shearing forces on the rocks. An example of this type of fault is the San Andreas fault. Dip-slip faults are faults on which the movement is parallel to the dip of the fault surface. Normal faults are Dip-Slip faults on which the rocks above the fault surface, called the hanging wall, move down relative to the rocks below the fault surface which is the foot wall. Normal faults are the result of forces that pull rocks apart, usually called extension. An example of this fault is the reason the Sandias were made. A reverse fault occurs when the hanging-wall moves up in relation to the foot-wall. The reverse faults are very different from normal faults mainly because they are the result of compression. The Sierra Nevadas are a result of normal faulting A common term associated with earthquakes is the epicenter. The epicenter is the point on the Earth’s surface directly above where the earthquake has actually taken place. The focus of the earthquake is the point in the Earth where the quake actually originated. The device used to record earthquakes is called a seismograph. These devices basically record ground movement. The can be set up to record horizontal and vertical movement of the ground. Using this device seismologists can triangulate the epicenter of earthquakes because the speed of the waves produced are known to them. The vibrations produced by earthquakes are called seismic waves. There are three types of waves, Primary waves, Secondary waves and surface waves. Primary waves are the fastest, moving at about 7-9 km/s (p. 512 Tillery), so they are the first to be felt. These waves are compressional so they act like the coils of a spring when you stretch it and then let it go. Secondary waves are next moving at 2-5km/s (p. 512 Tillery), only a few seconds after the primary waves. They move up and down or side to side as they travel, like the ripple that moves along a rope when you snap it. Because of the nature of motion these waves cannot travel through liquid, but they can cause more damage than primary waves. Surface waves are basically Secondary waves that travel on the surface. There are two main types of waves within the categories of Surface waves. One type is the Love wave. Love waves have no vertical displacement; and move the ground from side to side in a horizontal plane but at right angles to the direction of travel. This horizontal shaking is very destructive to buildings. The second type is the Raleigh wave. It moves both vertically and horizontally in a vertical plane pointed in the direction in which the waves are traveling. The Richter Scale which is a system used to measure the strength of an earthquake. It was developed by Charles Richter in 1935 as a means of categorizing local earthquakes. It is a collection of mathematical formulas, it is not a physical device. Each unit represents about ten times more ground movement and thirty times more energy being released. The Richter Scale 0-2 Smallest detectable earthquake. 2-3 Detected and measured but not generally felt. 3-4 Felt as small quake but no damage occurs. 4-5 Minor earthquake w...