Haiti Earthquake

http://www.youtube.com/watch?v=fahz97JjeJ8&feature=channel

Chile Earthquake

http://www.youtube.com/watch?v=T7jaayXlm-M

chile ppt.ppt

What is an Earthquake?

A shake or vibration caused by the sudden

breaking or sliding of rock in

the Earth

Where do they happen?Fault - Fracture (break) in rock

where sliding occurs

As tectonic plates move, they slide past other plates.

At the edges they get stuck, but the plates keep moving.

Eventually, the rock gives and a fault is formed.

Elastic Rebound

Stress builds up between the two plates causing

the crust to warp

An earthquake allows that energy to be

released, and the plates return to their normal position (just shifted)

Stages of an Earthquake1.Inactivity

(1 ½. Foreshock small quake that can occurs hours or days before a

major earthquake)

2. Major Earthquake

3. Aftershock quakes that occur seconds to a year after a major

earthquake

TYPES OF FAULTS

Normal Fault

Reverse Fault

Strike Slip

Normal Fault

-blocks of rock move apart

-occur at divergent boundaries

Reverse Fault-blocks of rock move towards

each other

-occur at convergent boundaries

Strike Slip

-rocks move sideways past each

other

-occur at transform

boundaries

Earthquakes don’t always occur along a plate

boundary…New Madrid Fault

1811-1812

3 Magnitude 8 Earthquakes

How do we measure earthquakes?1.Richter Scale

-measures the height of seismic waves

-each whole number is 10 times the seismic wave height

-each whole number is 33 times more energy released

Richter Scale

> 8 Total destruction About 1/year

7-7.9 Bad 18/year

6-6.9 Moderate -serious 120/year

5-5.9 Minor damage (felt by everyone)

800/year

4-4.9 Not felt by everyone 6,000/year

< 3.9 Very small 1 million/year

Largest Earthquake on the Richter Scale:

9.5Chile

1960

How do we measure earthquakes?

2. Mercalli Intensity Scale

-the amount of damage an earthquake causes

-scale of I - XII

-very subjective

-typically used for building codes

Mercalli Scale

How do we measure earthquakes?

3. Moment Magnitude Scale

-combine how rigid the Earth is and the distance the Earth

moves along the fault

-scientists use this method the most

Predicting an Earthquake

1.Short-term ‘Forecasting’

-hours to weeks

-based on foreshocks

*not always foreshocks

Predicting an Earthquake2. Seismic Gap

-areas along faults that have not had recent earthquakes

-the more time without an earthquake, the greater the chance of an

upcoming earthquake

-larger earthquakes in the past -> more frequent earthquakes

Predicting an Earthquake

3. Recurrence Interval

-earthquakes along a fault tend to have relatively constant recurrence

patterns

ex: San Andreas Fault

-22 years between earthquakes of magnitude 5.5 or higher

Predicting an Earthquake

4. Anomalous Animal Behavior

-dogs barking

-chickens not laying eggs

-rats perched on power lines

*not considered scientific* though often evident

Deadliest Earthquakes1. Shaanxi, China 1556 -830,000

casualties

2. Tangshan, China 1976 – 255,000 casualties

3. Gansu, China 1920 – 234,117 casualties

4. Haiti 2010 -233,000 casualties

5. Indian Ocean (Sumatra) 2004 – 230,210 casualties

Tangshan, China

Animals also gave a warning that something was about to happen. One thousand chickens in Baiguantuan refused to eat and ran around excitedly chirping. Mice and yellow weasels

were seen running around looking for a place to hide. In one household in the city of

Tangshan, a goldfish began jumping wildly in its bowl. At 2 a.m. on July 28, shortly before the earthquake struck, the goldfish jumped out of its bowl. Once its owner had returned

him to his bowl, the goldfish continued to jump out of its bowl until the earthquake hit.

Chen Yong, et al, The Great Tangshan Earthquake of 1976: An Anatomy of Disaster (New York: Pergamon Press, 1988) 53.

Human Induced EarthquakesSeveral earthquakes have been

caused because of human activity

Examples: -building dams over inactive fault

zones (e’quake and flooding)

- Nuclear Explosions (Nevada test site)

*Some scientists think we should trigger ‘controlled quakes’ in California to reduce

potential damage

Seismic WavesAs energy is released from an

earthquake, it is distributed in waves

Seismic Waves

Body Waves

Travel through the interior of the Earth

Surface Waves

Travel along the Earth’s surface

Body WavesP - Waves

Primary Waves

- ‘pressure’ or ‘push – pull’ waves

- Travel fastest (few km/sec)

- Travel through all layers of Earth

Body WavesS – Waves

Secondary Waves

- ‘shear’ or ‘shape’ waves

- Travel slightly slower than P waves

- Do not travel through liquids (outer core)

Body Waves

Surface WavesR - Waves

Rayleigh Waves

- Make the ground ripple up and down

Surface WavesL - Waves

Love Waves

- Make the ground ripple side to side

Seismograph

http://snowball.millersville.edu/

~cws/seismic/current/Local_East-West/current.gif

An instrument that can record ground motion from an earthquake happening

anywhere on Earth

Locating an EarthquakeFocus

Spot in the crust where the fault begins to slip

*the deeper an earthquake, the less damage it causes at

the surface*

EpicenterPoint on Earth’s

surface directly above the focus

Locating an Earthquake

How to find an epicenter

-need 3 seismic stations to record

the event

-using the differences in arrival times, seismologists can determine the

distance of the station to the

epicenter

TriangulationWhen you connect the data from the 3 seismic stations, you will find

the epicenter

Earthquake Aftermath

Earthquakes themselves cause tremendous damage, but they also leave behind a

path of destruction

1. Ground DisplacementDepending on the fault, giant cracks in the Earth can form

Alaska 1964

Examples:

1964–Alaska– 12 m

1906–San Francisco– 7 m

2. LandslidesSoil and

Debris that is shaken during an

earthquake may loosen and cause a landslide

3. Liquefaction

Soil that has small

amounts of water in it, will act as a liquid during

an earthquake

Ex: Kobe, Japan 1995

4. Tsunami

Earthquakes that occur near

oceans create massive waves which act as a wall of water

Seismic sea wave

Sumatra 2004

5. FireDestruction during an

earthquake can cause large fires

Tokyo - 1923San Francisco - 1906