What is an earthquake An earthquake is a shaking of the ground caused by the sudden breaking and movement of large sections (tectonic plates) of the earth's rocky outermost crust. The edges of the tectonic plates are marked by faults (or fractures). Most earthquakes occur along the fault lines when the plates slide past each other or collide against each other. The shifting masses send out shock waves that may be powerful enough to alter the surface of the Earth, thrusting up cliffs and opening great cracks in the ground Earthquakes cause great damage; collapse of buildings and other man- made structures, broken power and gas lines (and the consequent fire), landslides, snow avalanches, tsunamis (giant sea waves) and volcanic eruptions.

Earthquakes are common events. The United States Geological Survey estimates that more than three million earthquakes occur on Earth each year, which is equivalent to more than 9,000 earthquakes per day. Virtually all of these are too small to be noticed by humans and many occur in remote areas far from the seismometers that measure earthquakes

What does an earthquake look like

What does an earthquake feels like? The way an earthquake feels depends on where you are, where the earthquake is, and how big the earthquake is: A large earthquake nearby will feel like a sudden large jolt followed quickly by more strong shacking that may last a few seconds or up to a couple of minutes if its a rare great event. The shaking will feel violent and it will be difficult to stand up. The contents of your house will be a mess. A large earthquake far away will feel like a gentle bump followed several seconds later by stronger rolling shacking that may feel like sharp shacking for a little while. A small earthquake nearby will feel like a small sharp jolt followed by a few stronger sharp shakes that pass quickly. A small earthquake far away will probably not be felt at all, but if you do feel it, it will subtle gentle shake or two that is easier to feel if youre still and sitting down.

What causes an earthquake? There are two main causes of earthquakes. Firstly, they can be linked to explosive volcanic eruptions; they are in fact very common in areas of volcanic activity where they either proceed or accompany eruptions. Secondly, they can be triggered by Tectonic activity associated with plate margins and faults. The majority of earthquakes world wide are of this type.

lithospheric plates Lithospheric plates are the plates that comprise the fractured surface of the earth. Lithospheric plates are of two types: continental plates comprised mostly of granitic-type rock rich in silica and aluminum (also called "genius") and oceanic plates comprised mostly of basaltic-type rocks rich in magnesium and aluminum (also called "sima"). Earthquake and volcanic activity is common along the boundaries of lithospheric plates.

What are tectonic plates? A tectonic plate (also called lithospheric plate) is a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. Plate size can vary greatly, from a few hundred to thousands of kilometers across; the Pacific and Antarctic Plates are among the largest. Plate thickness also varies greatly, ranging from less than 15 km for young oceanic lithosphere to about 200 km or more for ancient continental lithosphere (for example, the interior parts of North and South America).

Tectonic Earthquakes Tectonic earthquakes are triggered when the crust becomes subjected to strain, and eventually moves. The theory of plate tectonics explains how the crust of the Earth is made of several plates, large areas of crust which float on the Mantle. Since these plates are free to slowly move, they can either drift towards each other, away from each other or slide past each other. Many of the earthquakes which we feel are located in the areas where plates collide or try to slide past each other. Volcanic Earthquakes Volcanic earthquakes are far less common than Tectonic ones. They are triggered by the explosive eruption of a volcano. Given that not all volcanoes are prone to violent eruption, and that most are 'quiet' for the majority of the time, it is not surprising to find that they are comparatively rare. When a volcano explodes, it is likely that the associated earthquake effects will be confined to an area 10 to 20 miles around its base, where as a tectonic earthquake may be felt around the globe.

Are earthquake linked to volcanoes? There are 12 tectonic plates in total. These 12 plates float on the liquid magma and are currently moving in all different directions at all different speeds. Volcanoes are formed either when two plates move apart or when two plates collide. Volcanoes are a landform that is produced as lava cools. There are two main types of volcanoes: shield volcanoes and composite volcanoes. Shield volcanoes are made from mafic lava, have very gentle slopes and are found at constructive plate margins (where the plates are moving apart). An example of a shield volcano is the Hawaiian Islands.

Composite volcanoes on the other hand are from felsic (sandy) magma, are found in seduction zones (where the plates are moving together) and are high layered constructions. They are very explosive and are much more dangerous than shield volcanoes. An example of a composite volcano is Mount Pinatubo. Volcanoes have many effects on humans. They create islands that people may live on or use to gather resources. Then there are mountains, which are formed in three ways. First two plates collide creating fold mountains. This means that instead of one plate sliding under the other, they crash together and force the Earth's crust up, creating mountains. An example of a fold mountain is the Himalayas.

Facts about earthquakes Alaska has more earthquakes than any other state. The most violent earthquake ever recorded in the United States took place in Anchorage, Alaska in March It measured 8.4 on the Richter scale. More than 100 people died. Sand, mud, and water sometimes bubble up during earthquakes, gushing water and soil like miniature mud volcanoes. An earthquake can cause an avalanche or a landslide causing snow, rocks and mud to crash down from a mountain. A weaker earthquake can cause more damage and death than a stronger earthquake if its epicenters is in or close to large cities.

A typical Earthquake lasts under a minute. The Appalachian mountains in the United States were formed millions of years ago by thrust fault activity. Scientists predict that during the next 30 years, Californians have a 65 percent chance of experiencing an earthquake of magnitude 7 or greater. The safest buildings can bend back and forth without breaking from an earthquake. The moon has quakes too. The interior of Antarctica has icequakes, but these quakes happens on the ice sheet and not the land itself.

Everyday earthquakes Everyday there are about 3000 earthquakes. Most of them are so small that no one even notices them. Serious earthquakes that break up roads, bridges and building and kill and injure people are quite rare.

Earthquake damage Most earthquakes are so small that people living near them only notice the ground shaking slightly. Stronger earthquakes make trees and leaves shake and church bells ring. An even bigger earthquake makes chimneys and trees fall down. The worst earthquakes break up roads, railways and buildings. Whole towns may be destroyed and many people may be killed or injured and left homeless

A picture of a Taiwan School that collapsed after an earthquake in 1999.

An earthquake in Paso Robles, California caused this building to collapse into rubble.

From the Loma Preita Earthquake in A collapsed building destroys a car.

Causes of earthquakes Earthquakes are caused due to two major reasons. The first reason is the eruption of volcanoes, which are sudden, and as is known volcanoes are seat of inner disturbance and can effect the plates which is the second cause of earthquakes. Earthquakes are caused due to disturbance in the movement of plates, which again can be caused due to various reasons like under crust waves or cracks in the plates.

Tsunami is a series of sea waves most commonly caused by earthquakes beneath the sea floor. In the open ocean, tsunami waves travel at speeds of up to 600 miles per hour. Generated tsunamis: If a large earthquake displaces the sea floor near our coast, the first waves may reach the coast within minutes after the ground shaking stops. Distant-source tsunamis: Tsunamis may also be generated by very large earthquakes in other areas of the Pacific Ocean and may reach our coastline many hours after the earthquake occurred.

Preventing earthquakes An earthquake can sometimes be stopped by pumping water into the rocks so that the jammed plates slip past each other. A small underground explosion can also make the plates move safely

Earthquake Survival Kits SURVIVAL SUPPLIES Water-2 quarts to 1 gallon per person, per day. First Aid Kit-ample, and freshly stocked. First Aid Manual-know how to use it. Food-canned or individually packaged; precooked, requiring minimum heat and water. Consider infants, pets, and other special dietary requirements. Critical medication, extra eyeglasses Can opener Blankets Radio-portable battery operated, spare batteries Critical medication and eyeglasses, contact cases and supplies Fire Extinguisher-dry chemical, type ABC

Flashlight-spare batteries and bulbs Watch or clock-battery or spring wound. COOKING: Barbeque-use outdoors ONLY-charcoal and lighter, or Sterno stove Plastic bags-various sizes, sealable Pots-at least two Paper plates, plastic utensils, and paper towels SANITATION Large plastic trash bags-for trash, waste, water protection Ground cloth Large trash cans Hand soap, liquid detergent, shampoo Toothpaste, toothbrushes, dental floss Deodorant Feminine supplies Infant supplies Toilet paper Powdered chlorinated lime-to add to sewage to disinfect and keep away insects. Newspapers-to wrap waste, garbage; may also be used for warmth.

Mini Survival Kit for Automobile Non-perishable food-store in coffee cans Boiled water First aid kit and manual Fire extinguisher Blanket Sealable plastic bags Flashlight-spare fresh batteries and bulb Critical medication, extra eyeglasses Tools-screwdriver, pliers, wire, knife Short rubber hose Pre-moistened towelettes Feminine supplies Sturdy shoes and gloves

Earthquake pictures

Earthquake graphs