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Roger Weller, geology instructor

by Lauren Williams
Physical Geology
Spring 2012








An earthquake is defined as a sudden release of energy in the Earth’s crust or upper mantle that causes seismic waves. They are very dangerous and can cause serious damage and loss. Earthquakes have been known to destroy land, architecture, and take away the lives of many. It’s no surprise that earthquakes are classified as a natural disaster. 


















One of the most common terms associated with Earthquakes is called the “Ring of Fire.” The Ring of Fire encircles the Pacific Ocean and is approximately 25,000 miles long. It is estimated that between 80% and 90% of the world’s earthquakes occur along here due to the high volcanic activity.














Plate tectonics are a theory that the lithosphere of the earth is divided into plates that float on the mantle and collide with each other, slide under each other, or move past adjacent plates.  There are seven major plates. They are known as: the Pacific Plate, the North American Plate, the South America Plate, the Africa Plate, the Eurasia Plate, and the Australia Plate. Plates also fall under the two categories of oceanic and continental. Plate collisions can cause coastal volcanoes, island arcs, and mountain chains. Although plate collisions can create different types of landforms in some areas they merely slide along each other, which means they neither create nor destroy land.
















An earthquake fault is a break in the earth’s crust where the movement of the plates takes place.

There are three major types of Earthquake faults.














 From top to bottom-
     Normal Fault
     Reverse Fault

     Strike-Slip fault



     A normal fault is a fault where the hanging wall moves down to the footwall due to extension. A reverse fault is a fault where the hanging wall moves up to the footwall due to compression. A strike-slip fault is a fault where two block of crust slide past each other on the same plane as each other.


There are also different boundaries associated with earthquakes: divergent, convergent, and transform-fault. A divergent boundary is created as plates pull away from each other. Oceans are created due to divergent boundaries. A convergent boundary is when one plate goes under the other. Mountains and volcanoes are often formed when plates converge. Transform-Fault boundaries occur when plates slide past each other. Most of these are found on the ocean floor.




















   The Richter scale was invented in 1935 by a man named Charles F. Richter. This scale is extremely important to those who study earthquakes and also for those who need to be watching for earthquakes. It is used to measure the intensity of the earthquake. The intensity is measured and then calculated into numbers from zero to ten that correspond with the level of intenseness. The largest earthquake every recorded on the Richter scale was a 9.5. Most earthquakes are called tremors and are not felt by humans though. 


















Now let’s discuss some precautions that can be taken. The most obvious one is to make sure your home is back away from the fault lines. There are special maps that have earthquakes recorded on them, which makes this fairly easy. There are also ways to check for with the county or city to see if geological studies have been done on certain land sites. Here are some examples of these maps: