Earthquakes BY JOHNATHAN EVANS What Exactly is an Earthquake? An Earthquake is what happens when two blocks of the earth are pushing against one another and then suddenly slip past each other. The surface where they slip past each other is called the fault or fault plane. The area below the earth’s surface where the earthquake starts is called the Hypocenter, and the area directly above it on the surface is called the “Epicenter”. What are aftershocks/foreshocks? Sometimes earthquakes have Foreshocks. Foreshocks are smaller earthquakes that happen in the same place as the larger earthquake that follows them. Scientists can not tell whether an earthquake is a foreshock until after the larger earthquake happens. The biggest, main earthquake is called the mainshock. The mainshocks always have aftershocks that follow the main earthquake. Aftershocks are smaller earthquakes that happen afterwards in the same location as the mainshock. Depending on the size of the mainshock, Aftershocks can keep happening for weeks, months, or even years after the mainshock happened. Why do earthquakes happen? Earthquakes happen because all the rocks that make up the earth are full of fractures. On some of the fractures that are known as faults, these rocks slip past each other when the crust rearranges itself in a process known as plate tectonics. But the problem is, rocks don’t slip past each other easily because they are stiff, rough and their under a lot of pressure from rocks around and above them. Because of that, rocks can pull at or push on each other on either side of a fault for long periods of time without moving much at all, which builds up a lot of stress in the rocks. When they finally do move past each other, so much pressure has been built up that it causes an earthquake. Where do earthquakes happen at? Most earthquakes,(including the largest and most powerful) commonly occur near the edge of oceanic and continental plates(the earth’s crust is made up of several pieces, called plates. The plates under the oceans are called oceanic plates and the rest are called continental plates.) How powerful are earthquakes? Earthquake strength is measured by the Richter scale. The Richter scale measures these earthquakes from small earthquakes such as a 2.3 earthquake or a powerful one such as a 8.5 earthquake. Earthquakes are measured using a machine called a Seismometer which produces a seismograph. A Richter scale is normally numbered 1-10, though there is no upper limit. Pangea Pangea was a super continent that existed about 250million years ago and consisted of every single continent that exists today. About 175million years ago, There was a massive earthquake in Pangea which broke it apart into all the normal continents we have today *This is just what people think Pangea might have looked like. Mount Tai earthquake The mount Tai earthquake is very important because it was the first recorded earthquake in history. It occurred at Mount Tai during the 7th year of the reign of King Fa from the Xia dynasty between circa 2205 and 1600 BCE. Mount Tai earthquake cont. Mount Tai is located in western Shandong, just north of the city of Tai'an and to the south of the provincial capital Jinan. The mount tai earthquake has been dated to 1831 or 1731 BCE. Sparta earthquake The Sparta earthquake had a magnitude of 7.2 and occurred along the Sparta fault in the year 464 BCE and destroyed much of what was Sparta and many other City-states in Ancient Greece. Sparta earthquake cont. Historical sources suggest that the Sparta earthquake may have had a casualty toll of almost 20,000 although modern scholars suggest that this figure is likely an exaggeration. Sparta was located on what is now called the Hellenic arc which has a high amount of large seismic activity. Rhodes earthquake The Rhodes earthquake occurred at 3:00 in the morning on may 3rd, 1481 and was very powerful, having a magnitude of 7.1. The earthquake destroyed a statue of The colossus of Rhodes which was one of the tallest statues of the ancient world. Rhodes earthquake cont. The Rhodes earthquake also caused many casualties because it triggered a small tsunami, Which caused local flooding. It was the largest of a series of earthquakes that affected Rhodes, starting on 15 march 1481, continuing until January 1482. Tsunamis Tsunamis are enormous tidal waves that occur because of strong earthquakes (6.5 or more) occurring below or close enough to the ocean to cause the shifting of tectonic plates below the water. Tsunamis are very dangerous because they can travel as far as 10 miles inland, depending on the shape and slope of the shoreline. California Earthquakes. The reason California has so many earthquakes is that the earthquakes there are caused by the movement of huge blocks of the earth's crust called the northern and pacific plates. The pacific plate is constantly moving northwest so it is scraping horizontally past North America at a speed of about 50 millimeters (or 2 inches) per year. Largest earthquake ever. The world's largest earthquake (with an instrumentally documented magnitude) occurred on May 22, 1960 near Valdivia, in southern Chile.it had a magnitude of 9.5 and is referred to as the "Great Chilean Earthquake" and the "1960 Valdivia Earthquake. The United States Geological Survey reports this event as the "largest earthquake of the 20th Century." Largest earthquake ever cont. The worlds largest earthquake also produced a powerful tsunami that traveled at a speed of about 200 miles per hour across the Pacific Ocean. Other earthquakes in history might have been larger however this is the largest earthquake that has occurred since accurate estimates of magnitude became possible in the early 1900s..