Earthquakes

Earthquakes can be one of the most deadly and destructive forces to hit a region. They can also be so small that they are not even felt and cause no damage. Some regions of the earth are more prone to quakes because of how close they are to faults. The deadliest earthquake occurred in china in 1556. Because the people lived in caves that collapsed during the quake 830,000 people died. The second deadliest earthquake also struck China in the city of Tangshan in 1976 and 242,000 people died. Now that we know where earthquakes are most likely to happen, buildings and houses can be built to withstand all earthquakes but the worst earthquakes. Unlike hurricanes, tornados and other deadly storms, weather has no effect on when or where an earthquake can occur. Since earthquakes start far below the earth surface barometry pressure has no part in their occurrences.

It is important to understand the terms used in association with earthquakes. An earthquake is measured in magnitude and intensity. Magnitude measures the size of the earthquake and is the same even if the amount of shaking or tremors varies in different places. Intensity reports for an earthquake can be very different from the same earthquake because it is based on peoples experiences of the quake. Seismic waves are the vibrations that result from the shock of rock moving along the fault in an earthquake. They travel out in all directions from the focus. The focus of an earthquake is the place underground where it starts, and the epicenter is the surface location of the earthquake. Seismographs are the instruments that measure the seismic waves. Tectonic plates are the huge rocky plates that make up the outer layer of the earth. A fault is the fracture in the rocks where the plates meet and rupture because of movement, earthquakes can cause tsunamis which are huge waves caused by an earthquake in the ocean floor. An earthquake produces two basic kinds of waves, body waves which come from the focus to the surface and surface waves which are transformed body waves. There are a few kinds of body waves, p waves that travel the fastest and are the first waves felt in an earthquake and s waves which are slower and cant travel through liquid but move vertically and horizontally and cause much more damage than p waves.

Earthquakes are though to be caused when the tectonic plates shift and grind into one another. Scientists have plotted earthquake epicenters on a map and have seen that almost all quakes occur in certain belts. They have also recorded the depth of all the quakes and together the information shows that most quakes occur along the areas where the tectonic plates meet. This is called plate tectonics. There have been earthquakes that have occurred far from plate boundaries which scientists have no explanation for such as the huge quake in America in 1811-12

Earthquakes are measured on two different scales. The Mercalli scale