Today we’ll learn the answers to:1. What are earthquakes?2. How do earthquakes occur?3. What are the effects of

earthquake?4. How can we protect ourselves from earthquakes?5. Chilean earthquake 1960

WH

AT

AR

EE

AR

TH

QU

AK

ES

?

An earthquake is the result of a sudden release of energy in

the Earth's crust that creates seismic waves. The seismic

activity of an area refers to the frequency, type and size of

earthquakes experienced over a period of time.

Earthquakes are measured using observations from

seismometers. The moment magnitude is the most common

scale on which earthquakes larger than approximately 5 are

reported for the entire globe. The more numerous

earthquakes smaller than magnitude 5 reported by national

seismological observatories are measured mostly on the

local magnitude scale, also referred to as the Richter scale.

These two scales are numerically similar over their range of

validity. Magnitude 3 or lower earthquakes are mostly almost

imperceptible or weak and magnitude 7 and over potentially

cause serious damage over larger areas, depending on their

depth.

HOW DO EARTHQUAKES OCCUR?

Most earthquakes are causally related to compressional or

tensional stresses built up at the margins of the huge moving

lithospheric plates that make up the earth's surface. The

immediate cause of most shallow earthquakes is the sudden

release of stress along a fault, or fracture in the earth's crust,

resulting in movement of the opposing blocks of rock past

one another. These movements cause vibrations to pass

through and around the earth in wave form, just as ripples

are generated when a pebble is dropped into water. Volcanic

eruptions, rockfalls, landslides, and explosions can also

cause a quake, but most of these are of only local extent.

Shock waves from a powerful earthquake can trigger smaller

earthquakes in a distant location hundreds of miles away if the geologic conditions are favorable.

• Ground ruptureShaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures.

•FloodsFloods may be secondary effects of earthquakes, if dams are damaged. Earthquakes may cause landslips to dam rivers, which collapse and cause floods.

•FiresEarthquakes can cause fires by damaging electrical power or gas lines.

•Avalanches and landslidesEarthquakes, along with severe storms, volcanic activity, coastal wave attack, and wildfires, can produce slope instability leading to landslides, a major geological hazard.

•Loss of life and damage to propertiesAn earthquake may cause injury and loss of life, road and bridge damage, general property damage, and collapse or destabilization (potentially leading to future collapse) of buildings. The aftermath may bring diseases and lack of basic necessities such as food and clean drinking water.

Loss of life and damage to

properties

Fires

Tsunamis and floods

Avalanches and landslides

HOW CAN WE PROTECT OURSELVES FROM

EARTHQUAKES?If you are…•Indoors: Drop, cover, and hold on.Drop to the floor, take cover under a sturdy desk or table, and hold on to it firmly. Be prepared to move with it until the shaking stops. If you are not near a desk or table, drop to the floor against the interior wall and protect your head and neck with your arms. Avoid exterior walls, windows, hanging objects, mirrors, tall furniture, large appliances, and kitchen cabinets with heavy objects or glass. Do not go outside!

•In bed: If you are in bed, hold on and stay there, protecting your head with a pillow. You are less likely to be injured staying

where you are. Broken glass on the floor has caused injury to those who have rolled to the floor or tried to get to doorways.

•Outdoors: Move to a clear area if you can safely do so; avoid power lines, trees, signs, buildings, vehicles, and other hazards.

•Driving: Pull over to the side of the road, stop, and set the parking brake. Avoid overpasses, bridges, power lines, signs and other

hazards. Stay inside the vehicle until the shaking is over. If a power line falls on the car, stay inside until a trained person removes the wire.

•In a high-rise: Drop, cover, and hold on. Avoid windows and other hazards. Do not use elevators. Do not be surprised if

sprinkler systems or fire alarms activate.

•In a stadium or theater: Stay at your seat and protect your head and neck with your arms. Don't try to leave

until the shaking is over. Then walk out slowly watching for anything that could fall in the aftershocks.

•Below a dam: Dams can fail during a major earthquake. Catastrophic failure is unlikely, but if you live downstream from a

dam, you should know flood-zone information and have prepared an evacuation plan.

> If you are at the beach, move to higher ground immediately - no matter how small the earthquake.

> If you are in a tsunami hazard zone and the earthquake is very strong, immediately

gather your family members, grab your tsunami disaster kit, and WALK to a safe area.

> If evacuation is impossible, go to the upper floor of a sturdy building or climb a tree. This should only be a last resort.

> Do not wait for an official warning.

Chilean earthquake 1960

The 1960 Valdivia earthquake or Great Chilean Earthquake of Sunday, 22 May 1960 was the most powerful earthquake ever recorded, rating 9.5 on the moment magnitude scale. It occurred in the afternoon (19:11 GMT, 15:11 local time), and lasted approximately 10 minutes. The resulting tsunami affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, southeast Australia, and the Aleutian Islands.

The epicenter was near Lumaco , approximately 570 kilometres (350 mi) south of Santiago, with Valdivia being the most affected city. The tremor caused localisedtsunamis that severely battered the Chilean coast, with waves up to 25 meters (82 ft). The main tsunami raced across the Pacific Ocean and devastated Hilo, Hawaii. Waves as high as 10.7 metres (35 ft) were recorded 10,000 kilometers (6,200 mi) from the epicenter, and as far away as Japan and the Philippines.