Ch 19 Earthquakes
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Transcript of Ch 19 Earthquakes
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.