Geological Hazards: Earthquake

Earthquake is is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Theseismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.

There are different types of earthquake and this are tectonic and volcanic earthquake.Tectonic earthquake is caused by the movements of tectonic plates while Volcanic earthquake is caused by an volcanic activity.

Earthquakes are caused by faulting, a sudden lateral or vertical movement of rock along a rupture (break) surface.

Focus is the source  of the earthquake, it is the point of origin or the hypocenter. The Epicenter is the point surface directly above the focus.

Aftershock is an earthquake that occurs after a previous earthquake, the mainshock. An aftershock is in the same region of the main shock but always of a smaller magnitude.  Foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space.

Seismograph is a sensitive instrument use to detected the seismic wave of the eartquake

Magnitude and Intensity measure different characteristics of earthquakes. Magnitude measures the energy released at the source of the earthquake. Magnitude is determined from measurements on seismographs. Intensity measures the strength of shaking produced by the earthquake at a certain location. Intensity is determined from effects on people, human structures, and the natural environment.

Ritcher Scale is a scale used to measure magnitude or amount of energy released at the focus.  Rossi–Forel scale was one of the first seismic scales to reflect earthquake intensities.
What to Do During an Earthquake

• Stay calm! If you're indoors, stay inside. If you're outside, stay outside.
• If you're indoors, stand against a wall near the center of the building, stand in a doorway, or crawl under heavy furniture (a desk or table). Stay away from windows and outside doors.
• If you're outdoors, stay in the open away from power lines or anything that might fall. Stay away from buildings (stuff might fall off the building or the building could fall on you).
• Don't use matches, candles, or any flame. Broken gas lines and fire don't mix.
• If you're in a car, stop the car and stay inside the car until the earthquake stops.
• Don't use elevators (they'll probably get stuck anyway).

What to Do After an Earthquake

• Check yourself and others for injuries. Provide first aid for anyone who needs it.
• Check water, gas, and electric lines for damage. If any are damaged, shut off the valves. Check for the smell of gas. If you smell it, open all the windows and doors, leave immediately, and report it to the authorities (use someone else's phone).
• Turn on the radio. Don't use the phone unless it's an emergency.
• Stay out of damaged buildings.
• Be careful around broken glass and debris. Wear boots or sturdy shoes to keep from cutting your feet.
• Be careful of chimneys (they may fall on you).
• Stay away from beaches. Tsunamis and seiches sometimes hit after the ground has stopped shaking.
• Stay away from damaged areas.
• If you're at school or work, follow the emergency plan or the instructions of the person in charge.
• Expect aftershocks.

Sources:
http://en.wikipedia.org/wiki/Earthquake
http://www.soest.hawaii.edu/GG/ASK/earthquakes.html
http://www.thetech.org/exhibits/online/quakes/seismo/
http://earthquake.usgs.gov/learn/topics/mag_vs_int.php
http://www.geo.mtu.edu/UPSeis/bda.html