Chatper 4 Flashcards
What are earth quakes?
Violent displacement and shaking of earth materials along faults and fractures, caused by a sudden release of engrergy
-Usually unpredictably
More then 13 million people have died bue to earth quakes in the part 4000 years
Early explanations of earthquakes
Culturally people thought earth rested on a super organism whose movement caused earthquakes
EX japan- giant cat fish
China- OX
Others believd it was a punishment from god
What ddi greek philosopher- Aristotle do?
first to explain quakes by natural causes
Today geologists believes that quakes are related to plate tectonics
What is Seismology
the branch of science concerned with earthquakes
is when using an instrument SEISMOGRAPGH records, detects and measures vibrations produced by earth quakes
Three Categories of earthquakes
Shallow focus(less then 70km)
the shallower an earthquake, the more damage it can produce at the surface
Interdeiate focus(70-300 km)
Deep focus(bigger then 300km)
intermediate and deep-focus earthquakes are rarely destructive.
Where are shallow focus earthquakes found?
Mainly found at divergent and transform boundaries
Where are intermediate and deep focus earthquakes found?
At convergent boundaries
Seismic Waves
Earthquakes cause ground shaking by producing 2 main types of waves
Body waves: travek trhough earth
Surface Waves: travel along surface
Body waves produce what type of shaking
What are the two types of body wave
Sharp Shaking’
- P-Wave or Primary Waves(search up video on both)
Fast seismic waves
can travel through solids, liquids and gases
Move material froward and backward in direction of wave movement
2.Secondary Or Shear Waves
Slowers than P waves
Travel only trhough sloids
Move material perpendicular to the direction of wave movement
(up and down)
(contioues M)
Surface Waves produce what motion
Two types of Surface waves
Produce rolling or swaying motion
- Rayleigh Waves(Hvae no idea)(Video)
Behave like water waves
Move foward while particles of material move elliptical path in vertical plane in direction of wave
Moving side to side(faster)
2.Love Waves
Move like S-waves
Indiviual particles of material move back and forth in horizontal plane to the direction of wave travel
(like ocean waves)
(not like m bc surface is stable)
How to locate a earthquake
P,S,R,L waves are used
P are fastest, S trvale 1/2 of velocities of P
P and S travel focus to the surface
L and R follow the P and S at surface
L and R are last to arrive at the seismograpgh
how do you measure strength of an earthquake
Done by measuring the intenisty and magnitude of a quake
Intensity
A qualitative measure of tyoe of damage
It is subjective
Mercalli Intesity Scale
a common scale to measure earthquakes in US
Has tables with values from I to XII
Magnitude
A measure of engery released by quake
It is a quantitaive
Who made the most popular magnitude scale
F. Richter
Scale determined using information from seismograpghs
Based 10 logarithmic scale
-Defines magnitue as the log of the ratio of the amplitude of the seismic wave to an arbitary, minor amplitle
Ricther scael now succed by moment magnitude scale
Used by united state geologaicl survery for modern earthquakes or large magnitudes
