Unit 7: Dynamic Earth Topic: Earthquakes - T-Birds Earth...

Unit 7: Dynamic Earth Topic: Earthquakes

Time for a new note packet!

Sub-project 1: Earthquake Risk

International experience, including tragic lessons from recent large earthquakes, shows that the growth of earthquake prone communities, following the global processes of development and urbanization, commonly gives rise to seismic risk unless proper countermeasures are taken to prepare for future earthquakes and manage the risk. This is true as well for the countries of low and moderate seismicity taking into account that the risk value depends not only on the hazard level, but also on the aggregate elements at risk and their vulnerability to probable seismic influence. Thus, the proper approach to the problem of risk assessment and risk management should include consideration of all the contributing factors:

Hazard:

Living in seismic prone areas means that seismic risk is unavoidable. It is impossible to manage the risk through prevention of future earthquakes. But improvement of seismic hazard assessment and providing reliable seismological and engineering-seismological information for planning and design purposes is an important factor contributing to efficiency of risk management programs.

Exposure (elements at risk):

When earthquakes occur in uninhabited areas they are not considered as disasters. Sometimes civilization and urbanization make human beings more vulnerable to the natural phenomena. It happens, in particular, when there is high concentration of population and complicated infrastructure in earthquake prone zones. So, the processes of land use and urban planning as well as development of new technologies should take into account the existing seismic threat.

Vulnerability:

The bitter engineering truth is that earthquakes do not kill people, vulnerable buildings do. Though future earthquakes cannot be avoided, the community can improve seismic performance of buildings and lifelines, reconstruct or retrofit old structures and build new earthquake-resistant constructions, in particular, for residential and critical buildings.

Awareness:

Lack of awareness (as a psychological component of vulnerability) contributes to seismic risk considerably. It concerns people from every sector of the community, all members of which are to realize how to prepare for possible disasters, how to behave if an earthquake strikes and what to do after.

Earthquake

Shaking caused by rapid movement of

crustal rock

Plastic Mantle

Fault

Earthquake Fault

Shaking caused by rapid movement of

rock

Crack within the Earth where the rock slips, or

moves

One Famous Fault in the USA The San Andreas Fault in California

Focus

Earthquake Fault Focus

Shaking caused by rapid movement of

rock

Crack within the Earth where the rock slips, or

moves

In the Earth where the earthquake occurs

Epicenter

Earthquake Fault Focus

Epicenter

Shaking caused by rapid movement of

rock

Crack within the Earth where the rock slips, or

moves

In the Earth where the earthquake occurs

On the surface directly above the focus

Topic: Seismic (Earthquake) Waves

Energy waves from an earthquake

1) P-waves (Primary)

2) S-waves (Secondary)

3) L-waves (Surface Waves)

Seismic Waves

1. Primary (P) Waves

2. Secondary (S) Waves

3. Surface (L) Waves

Compression waves First Fastest Through solid, liquid, gas

Shear waves Second Slower Through solids only

Surface waves Slowest Cause most damage

Seismograph

Used to detect the strength of an earthquake and

location

Japan Earthquake, 3/11/2011 Skidmore College, NY Seismograph

YOUR BEST FRIEND

Page 11

Richter Scale

(Magnitude)

Measures the

magnitude (the

amount of

energy released)

Mercalli Scale –

Measures intensity,

the earthquake’s

effect on people

and buildings.

Moment Magnitude Scale

Explained

http://www.iris.edu/hq/programs/education_

and_outreach/animations/26

Crust

Mantle

Outer Core Inner

Core

Simple Model of Earth’s

Interior

Waves refract (bend) in different densities

Earthquake waves tell us what the interior of the Earth is like!

We believe the outer core is a liquid because S-waves stop at this layer.

Time to Review

http://www.usgs.gov/ for Real Time Earthquakes

What type of wave?

What type of wave?

What is this point called?

Earth’s surface

Focus

What is this point called?

Earth’s surface

Focus

Epicenter

Final Question

Which seismic wave type travels the slowest?

Final Question

What is the name given to a location where an earthquake originates?