Earthquakes Haiti 12 th Jan 2010 New Zealand 3 rd Sept 2010 7.0 magnitude Focus depth: 8.1 miles deep Fault line that was previously undetected Epicentre:

Earthquakes

Haiti 12th Jan 2010New Zealand 3rd Sept 2010

7.0 magnitudeFocus depth: 8.1 miles

deepFault line that was

previously undetectedEpicentre: 25 miles

from Port au Prince Deaths: 230,000

7.0 magnitudeFocus depth: 7.5 miles

deepThe Alpine and the

Hope faultsEpicentre: 35 miles

from ChristchurchDeaths: 0

Case Studies

Why with so many similarities between the two earthquakes, did so many die in the Haiti

earthquake?

Haiti 12th Jan 2010New Zealand 3rd Sept 2010

Poor nation (poorest country in the Northern Hemisphere)

Little experience with earthquakes (previously undetected fault line)

Non-existent building standards

4.53pm lots of people out in the streets

Wealthy developed country

More experience with earthquake (active fault line)

High construction codes

4.35am people asleep in their beds

Reasons:

Haiti

http://www.bbc.co.uk/news/10593447 6mts after the earthquake?

Earthquakes

Definition: Earthquakes are vibrations or tremors in the earth’s crust, and are caused by the movement of the plates which makes the crust stretch and tear. This increase in stress and pressure is greater than the strength of the rocks which suddenly give way along a fault line in the crust.

http://www.youtube.com/watch?v=IRXlHhxhq64

Earthquakes

Tremors: shock waves which travel out from the origin or focus of the earthquake

Focus: The point deep in the crust at which an Earthquake begins.

Epicentre: Directly above the Focus on the surface is the Epicentre. The Earthquake is strongest here.

P and S waves When an earthquake occurs, it

releases energy in the form of seismic waves that radiate from the earthquake focus in all directions.

The different types of energy waves shake the ground in different ways and also travel through the earth at different velocities.

The fastest wave, and therefore the first to arrive at a given location, is called the P wave. The P wave, or compressional wave, alternately compresses and expands material in the same direction it is traveling.

The S wave is slower than the P wave and arrives next, shaking the ground up and down and back and forth perpendicular to the direction it is traveling.

Earthquake Waves

Two types:1. P waves or compression waves, shake the

ground back and forth in the same direction as the wave is moving. These are very fast and do little damage, they can pass through a building in less than a second.

2. An S wave or shear wave, shakes the ground back and forth perpendicular to the direction the wave is moving. They arrive after the P waves as they travel more slowly, and can damage buildings.

Surface waves

A surface wave is a seismic wave that is trapped near the surface of the earth. (The Love and Rayleigh waves)

Earthquake Depth

Shallow earthquakes: Less then 70km below the surface (mid-ocean ridges, continental-continental plate collision & conservative plate boundaries)

Intermediate earthquakes: 70-300km below the surface (oceanic-continental plate collisions)

Deep earthquakes: Greater then 300km below the surface (oceanic-oceanic plate collision)

Measuring and recording Earthquakes

1. Seismographs2. The Richter Scale3. The Modified Mercalli Scale4. Moment Magnitude Scale

Seismograph

Sensitive instruments called seismographs record earthquake waves

Global Seismic Networks (GSN) is a web of 128 recording stations across the world

These detect earthquakes and help monitor nuclear tests

Seismograph Reading

P waves

S waves

Richter Scale

A scale which wasdevised by

Charles F. Richter. It is a measure of the amount of energy released by an earthquake.

Moment Magnitude Scale

The Moment Magnitude Scale is the successor to the Richter Scale and is today used by seismologists.

It measures the energy produced by earthquakes. It again goes from 1 upwards. At each step about 32 times more energy is released than at the previous step.

Modified Mercalli Scale

A measure of the observed effects of an earthquake

Seismologists seek information from people on the severity of earthquake effects

Roman numbers i to xii are used to show intensity of the earthquake

Modified Mercalli Scale