CH 19 EARTHQUAKES

Forces within Earth Stress= total force acting on crustal rocks per unit area

Strain= deformation of materials in response to stress

Fault = any fracture or

system of fractures along which earth moves.

= due to crustal rock failure when stress is too great

Types of Seismic Waves = vibrations of

ground made from an earthquake

Types:I. Body Waves:1. Primary (P)2. Secondary (s)II. Surface Waves:3. Surface

Earthquake WavesPrimary Waves

Aka – P waves Squeeze and push

rocks in the direction along which the waves are traveling.

Typically L to R

Secondary Waves

Aka – S waves Slower than p Second set of

waves to be felt. Moves at right

angles to the wave- “jump rope”

Surface Waves The 3rd type of

wave Slowest of all Sideways, up and

down movement Usually the most

destructive due to the most ground movement

Seismic Waves Spread from the

point of crustal rock failure

Point of wave origin is called FOCUS

Point directly above the FOCUS on the surface is called EPICENTER.

Interesting fact… The speed and

direction of seismic waves can determine the inside composition of the earth!

To review… Answer book

Questions 1-4 on page 533

19.2 Seismic Waves and Earth’s interior

Seismometer= a sensitive piece of equipment that measures the earth’s vibrations and disturbances

Seismogram= the written record produced by a seismometer.- These can be used to determine the epicenter of an earthquake based on the p and s wave recording times.

Travel time curves

Distance from the epicenter

19.3 Measuring and Locating Earthquakes

Richter Scale = the numerical rating system that measures the energy (aka -magnitude!) of the wave and the height (aka – amplitude) of it!

Richter Scale

To find the Magnitude: You must

measure the Height of the S wave.

This is called the AMPLITUDE

Nomogram Then you use

your Distance measurement along with your found Amplitude.

The line that connects the two will cross over the amplitude!

Modified Mercalli Scale Is a scale that

measures the DAMAGE done by the intensity of the earthquake.

19.4 Earthquakes and Society Earthquake

hazards are determined by many factors, can be identified, and then minimized.

I. Structural failures 1. Weak ground

floors -The supporting walls of the ground floor collapse, so the building begins to pancake.

Pancaking – When the bottom floors crumble allowing the upper layers to land on top – layer by layer

2. Wood or Cement? Wooden buildings are actually better

than cement buildings. The wood can bend a bit, while the cement building will crack apart!

3. Building Height… The taller the building, the more likely it

will vibrate with the waves and fall!

II. Land and Soil Failure 1. May trigger landslides in sloped areas

In 1970 in Peru, a 7.8 magnitude quake produced a landslide that buried several towns and killed an estimated 30,000 people

2. Soil Liquefaction Sand is really saturated with water and

the shaking allows the water to accumulate and cause it to act like a true liquid.

III. Tsunami Giant wave caused by vertical seafloor motions.