Earthquake

An earthquake (also known as a quake, tremor or temblor) is 
the result of a sudden release of energy in the Earth's crust that createsseismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.

Here are a few different types of earthquakes.
One type of earthquake is a tectonic earthquake that is caused by breaking rocks. Another type of earthquake is a volcanic earthquake that is caused by volcanic activity. Another type of earthquake is a collapse earthquake that is caused by a ground collapse. The last type of earthquake is an explosion earthquake that is caused by a chemical or nuclear explosion. 

       

A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as foreshock, mainshock or aftershock is only possible after the event.^[1]
An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock. Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the main shock.

Seismometers are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and otherseismic sources. Records of seismic waves allow seismologists to map the interior of the Earth, and locate and measure the size of these different sources

• Richter magnitude scale, a measure of the energy of an earthquake

Intensity: The intensity of an earthquake at a particular locality indicates the violence of earth motion produced there by the earthquake. It is determined from reported effects of the tremor on human beings, furniture, buildings, geological structure, etc. Many places, including Hong Kong, have adopted the Modified Marcella Scale (MMS) which classifies earthquake effects into twelve grades. -

• I. Microseismic tremor. Recorded by a single seismograph or by seismographs of the same model, but not by several seismographs of different kinds. The shock felt by an experienced observer.

• II. Extremely feeble tremor. Recorded by several seismographs of different kinds. Felt by a small number of persons at rest.

• III. Feeble tremor. Felt by several persons at rest. Strong enough for the direction or duration to be appreciable.

• IV. Slight tremor. Felt by persons in motion. Disturbance of movable objects, doors, windows, cracking of ceilings.

• V. Moderate tremor. Felt generally by everyone. Disturbance of furniture, ringing of some bells.

• VI. Strong tremor. General awakening of those asleep. General ringing of bells. Oscillation of chandeliers, stopping of clocks, visible agitation of trees and shrubs. Some startled persons leaving their dwellings.

• VII. Very strong tremor. Overthrow of movable objects, fall of plaster, ringing of church bells. General panic. Moderate to heavy damage buildings.

• VIII. Damaging tremor. Fall of chimneys. Cracks in the walls of buildings.

• IX. Devastating tremor. Partial or total destruction of buildings.

• X. Extremely high intensity tremor. Great disaster, ruins, disturbance of the strata, fissures in the ground, rock falls from mountains.

Magnitude: Magnitude is a measure of the amount of energy released during an earthquake. It may be expressed using several magnitude scales. One of these, Used in Southern California, is called the Richter scale. To calculate magnitude, the amplitude of waves on a seismogram is measured, correcting for the distance between the recording instrument and the earthquake epicentre. Since magnitude is representative of the earthquake itself, there is thus only one magnitude per earthquake. 

ROSSI FORREL SCALE: The Rossi–Forel scale was one of the first seismic scales to reflect earthquake intensities. Developed by Michele Stefano Conte de Rossi of Italy and François-Alphonse Forel of Switzerland in the late 19th century, it was used for about two decades until the introduction of the Mercalli intensity scale in 1902.

The 1873 version of the Rossi–Forel scale had 10 intensity levels:

The Richter magnitude scale (often shortened to Richter scale) was developed to assign a single number to quantify the energy released during an earthquake.

The scale is a base-10 logarithmic scale. The magnitude is defined as the logarithm of the ratio of the amplitude of waves measured by a seismograph to an arbitrary small amplitude. An earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0, and corresponds to a 31.6 times larger release of energy.^[1]

Since the mid-20th century, the use of the Richter magnitude scale has largely been supplanted by the moment magnitude scale (MMS) in many countries. However, the Richter scale is still widely used in Russia and other CIS countries. Earthquake measurements under the moment magnitude scale in the United States—3.5 and up, on the MMS scale—are still usually erroneously referred to as being quoted on the Richter scale by the general public, as well as the media, due to their familiarity with the Richter scale as opposed to the MMS.

-Before an earthquake: Have a battery powered radio, flash light, and first aid kids in your house , Make sure everyone knows where they are kept , Learn first aid; teach how to stop electric main and gas supply , Don’t keep heavy objects in high shelves , Fasten heavy appliances to the floor, and anchor heavy furniture to the walls , Plan for your family for reuniting after an earthquake if anybody separated , Urge your school teachers to discuss earthquake safety in the class rooms, and ask them to conduct drills ,Keep some dry fruits and drinking water. Find out your office has an emergency plan, know your responsibility at your works during an emergency .Keep some dry fruits and drinking water . 

-During an earthquake: Stay calm if you are inside a building, and stay out if you are out of buildings. Many injuries occur as people enter or leave the buildings. If you are indoors , stand against the a wall near the centre of the building, or get under a sturdy table keep some cushion on your head, Stay away from windows and outside doors, if you are in a high rise building stand against a support column. If you are in outdoor stay in the open places , keep away from over head electric wires, and bridges, Don’t use open flames, if you are in a moving vehicle stop away from over bridges and stay inside the vehicle still earthquake stops

-After an earthquake: Check yourself and nearby people for injury, provide first aid, Check electric and gas connection, Turn on your radio or T.V for emergency instructions, reduce the use of phone lines it may be required for conveying some important messages. Stay out of damaged buildings, Wear chapels and gloves to protect against shattered glass and debris. Stay away from water front areas where tsunami could strike even after earthquake. Have one earthquake alarm fixed in your house.