What is Earthquakes? • Earthquake (also known as a quake, tremor or temblor) is the perceptible shaking of the surface of the Earth, which can be violent enough to destroy major buildings and kill thousands of people. The severity of the shaking can range from barely felt to violent enough to toss people around. Earthquakes have destroyed whole cities.

• Earthquakes are the vibrations caused by rocks breaking under stress.The underground surface along which the rock breaks and moves is called a fault plane.

• An earthquake is caused by a sudden slip on a fault. The tectonic plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the earth's crust and cause the shaking that we feel.

EARTHQUAKES

Types of earthquakesThere are four different types of earthquakes: Tectonic, volcanic, collapse and explosion.

1. Tectonic earthquake is one that occurs when the earth's crust breaks due to geological forces on rocks and adjoining plates that cause physical and chemical changes.

2. Volcanic earthquake is any earthquake that results from tectonic forces which occur in conjunction with volcanic activity.

3. Collapse earthquake are small earthquakes in underground caverns and mines that are caused by seismic waves produced from the explosion of rock on the surface.

4. Explosion earthquake is an earthquake that is the result of the detonation of a nuclear and/or chemical device.

Why do earthquakes happen?Earthquakes are usually caused when rock underground

suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don't just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up. When the rocks break, the earthquake occurs. During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again. The spot underground where the rock breaks is called the focus of the earthquake. The place right above the focus (on top of the ground) is called the epicenter of the earthquake.

HOW TO SURVIVE IN EARTHQUAKE?

TSUNAMI

What is Tsunami? Tsunami is a Japanese word with the English translation,

"harbor wave." "tsu," means harbor, while the bottom character, "nami," means "wave." In the past, tsunamis were sometimes referred to as "tidal waves" by the general public, and as "seismic sea waves" by the scientific community. The term "tidal wave" is a misnomer; although a tsunami's impact upon a coastline is dependent upon the tidal level at the time a tsunami strikes, tsunamis are unrelated to the tides. Tides result from the imbalanced, extraterrestrial, gravitational influences of the moon, sun, and planets. The term "seismic sea wave" is also misleading. "Seismic" implies an earthquake-related generation mechanism, but a tsunami can also be caused by a nonseismic event, such as a landslide or meteorite impact.

A tsunami is a series of great sea waves caused by an under earthquake , landslide, or volcanic eruption. More rarely, a tsunami can be generated by a giant meteor impact with the ocean.

TSUNAMI PICTURES

How Earthquakes Cause Tsunamis?

The illustration below shows a subduction earthquake (one where a denser plates shifts below its neighboring plate, at left). Energy is transferred and the displaced water forms a wave. As the wave travels and enters shallower water in the coastal area, it begins to increase in amplitude.

How Landslides Cause Tsunamis

Landslides are similar to volcanoes that avalanche into the sea. They occur in the water and often are triggered by earthquakes. There is an instance in 1958 where a tsunami was caused by rockfall in Lituya Bay, Alaska. In this instance, a gigantic boulder was loosed by an earthquake and fell into the bay causing a tsunami that went out to sea.

How Volcanoes Cause Tsunamis

There are two different ways that volcanoes can cause seismic waves. One possibility is for a land-based volcano to break down and collapse, forcing large amounts of ash and debris into the water. This sudden change and displacement of the water column transfers to kinetic energy and results in waves. More debris can create a bigger increase in wave amplitude and number.