Earth-quakes

ObjectivesIdentify causes of earthquakesDistinguish between S waves, P

waves, and surface wavesDescribe how earthquakes are

measured and ratedTriangulate to find the location of an

earthquakeDiscuss the types of damage that

can occur

What are earthquakes?

Earthquakes are vibrations caused by movement of rocks sliding past each other.

Where are they most common? These movements

of rocks are more common at plate boundaries

California and Japan have many earthquakes because they are on plate boundaries.

Earth’s Plates shown from earthquakes

Top 10 since 1900…Rank Date Location Magnitude Estimated Deaths/Damages (USD)

1 1960 Chile 9.5 1,655/$6 million 2 1964 Alaska 9.2 128/$300 million

3 2004 W. Sumatra 9.1 227,898/estimated in the billions

4 1952 Russia 9.1 none reported/$1 million

5 1906 Ecuador 8.8 500-1500/unknown

6 1965 Alaska 8.7 none reported/$10,000

7 2005 N. Sumatra 8.6 1300/unknown8 1950 Tibet 8.6 780/$25 million

9 1957 Alaska 8.6 none reported/$5 million

10 2007 S. Sumatra 8.5 21/unknown

Where will Haiti fit in?

In terms of magnitude it won’t be in the top 10

Magnitude 7.0

In terms of destruction and loss of life it will

Already 80,000 buried in mass graves

The number dead may reach over 200,000

Haiti

Let’s take a look around Port-Au-Prince

Earthquake motion

Since the earth’s surface is in motion, rocks in the lithosphere sometimes slip past each other

Well maybe slip isn’t a good word for this, maybe they GRIND past each other

This Grinding caused shock waves that move through the earth

The ground can move in different directions…

They can move

sideways

They can move up and down

They can push up a

section

They can not break the surface

Earthquakes occur where the ground was Stuck

The forces build up until the

fault breaks – releasing

energy

Some terms

The focus is where the earthquake occurs

The fault is the plane that the earth slides along

The epicenter is the point on the surface above the focus – it might not be on the fault

Seismic Waves start from the focus

Measured by a seismograph

It looks like the needle is moving, but the earth moves under the needle

Orders of Magnitude – The Richter scale

Not all earthquakes are the same

At magnitude 6, the ground moves 1 meter at the focus

At magnitude 7, the ground moves 10 meters

What it feels like

The Mercalli Scale

There are three types of waves

Primary wavesSecondary wavesSurface waves

P waves

Called Primary or Longitudinal waves

Compress and release Travel fastest Can travel through earth’s core but do bend (refract)

S-waves

Secondary or Transverse waves

Move up and down (S shaped)

Do not travel through earth’s core

Surface Waves

Rolling up/down or right/left Occur on surface – like ocean waves Are the most destructive

The waves travel at different speeds

And bounce off different layers of rock

Distance to an earthquake

Found by looking at time between P waves and S waves reaching the seismograph

Calculations tell you the distance to the focus

It takes three seismographic measurements to triangulate where the earthquake is located

Using Triangulation

the web site is www.sciencecourseware.com/VirtualEarthquake/ VQuakeExecute.html

What are the dangers

Buildings collapseHaiti

Roads break up1989 Loma Prieta

Earthquake, San Fransisco

Land can rise or sink

1964 Alaska, some land rose 40 feet, some seafloor dropped 50 feet

Liquefaction Softer rock does not stay

together, landfill is some of the worst land to build on

Landslides1692 the town of Port Royal,

Jamaica slide into the ocean, it landed 50 feet below sea level

TsunamisDecember 26, 2004

Earthquake

Buildings split Land can “boil”

Tsunamigenesis

The farther away you are, the longer it takes for the tsunami to reach you, you have more time to react

Before and after

Shows debris lines on the coastline after the 2004 tsunami

Look back at your notes, Can you…

Identify causes of earthquakes

Distinguish between S waves, P waves, and surface waves

Describe how earthquakes are measured and rated

Locate and earthquake by triangulation

Discuss the types of damage that can occur