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Causes of earthquakes If seen broadly we can say that 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. Plate Tectonic Theory The outer layer of the earth is divided into many sections known as plates, which are floating on the molten magma beneath the earth’s crust. Now the movement of these plates is determined by the convection current in the molten magma. The heat makes these plates rise and vice versa. Therefore after intervals there are plates that get submerged in the molten magma and there plates that rise upwards and at times even new crust is formed from the molten magma which in turn forms a new plate until it connects itself with the already existing ones. At times these plates and can be pushed up to form mountains and hills and the movement is so slow that it is really hard to comprehend that there is any movement at all. The movement and the results come out to be visible suddenly. Now these plates are the bases on which the continents stand and when these plates move the continents also move. Most of the earthquakes occur on the edges of the plates where a plate is under one or across. This movement disrupts the balance and position of all plates, which leads to tremors, which are called earthquakes.

An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called

the epicente

How are earthquakes recorded? Earthquakes are recorded by instruments called seismographs. The recording they make is called a seismogram. (figure 4) The seismograph has a base that sets firmly in the ground, and a heavy weight that hangs free. When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not. Instead the spring or string that it is hanging from absorbs all the movement. The difference in position between the shaking part of the seismograph and the motionless part is what is recorded.

The mission of the National Earthquake Information Center (NEIC) is to determine rapidly the location and size of all destructive earthquakes worldwide and to immediately disseminate this information to concerned national and international agencies, scientists, and the general public. The NEIC/WDC for Seismology compiles and maintains an extensive, global seismic database on earthquake parameters and their effects that serves as a solid foundation for basic and applied earth science research.

The short answer is that earthquakes are caused by faulting, a sudden lateral or vertical movement of rock along a rupture (break) surface.     Here's the longer answer: The surface of the Earth is in continuous slow motion. This is plate tectonics--the motion of immense rigid plates at the surface of the Earth in response to flow of rock within the Earth. The plates cover the entire surface of the globe. Since they are all moving they rub against each other in some places (like the San Andreas Fault in California), sink beneath each other in others (like the Peru-Chile Trench along the western border of South America), or spread apart from each other (like the Mid-Atlantic Ridge). At such places the motion isn't smooth--the plates are stuck together at the edges but the rest of each plate is continuing to move, so the rocks along the edges are distorted (what we call "strain"). As the motion continues, the strain builds up to the point where the rock cannot withstand any more bending. With a lurch, the rock breaks and the two sides move. An earthquake is the shaking that radiates out from the breaking rock.

Earthquake If you are indoors when shaking starts: “DROP, COVER AND HOLD ON.” If you are not near a strong table or desk, drop to the floor against an interior wall and cover your head and neck with your arms. Avoid windows, hanging objects, mirrors, tall furniture, large appliances and cabinets filled with heavy objects. Do not try to run out of the structure during strong shaking.

If you are downtown, it is safer to remain inside a building after an earthquake unless there is a fire or gas leak. There are no open areas in downtown San Francisco far enough from glass or other falling debris to be considered safe refuge sites. Glass from high-rise buildings does not always fall straight down; it can catch a wind current and travel great distances. If you are in bed, stay there and cover your head with a pillow. Do not use elevators. If you use a wheelchair, lock the wheels and cover your head.

Fasten all shelves securely to the walls. Use brackets to attach wall units, bookcases, and other tall furniture to wall studs. Standard steel brackets are fine and easy to apply. Place large, heavy objects on lower shelves or on the floor. They might fall during an earthquake and the less distance they have to fall, the better. You can also screw objects onto things, such as a desk.

Prepare disaster supplies in advance

Flashlight with extra batteries (preferably one for each individual) Portable, battery-operated radio with extra batteries Purchase and use "self powered radios" and "self powered flashlights". Batteries will be hard to find, if you can find them. Some models will charge cell phones, but the cell phone towers may be damaged, even destroyed. Purchase and use "glow sticks". These are safer than candles, since you will be dealing with ruptured gas lines, flammable, explosive gas. First aid kit and manual Emergency food and water (some sources say you should have up to 2 weeks worth of extra food on hand in case rescue workers cannot reach your location) Nonelectric can opener Essential medicines Cash and credit cards Sturdy shoes for each family member.