

2 :

Foci – location inside earth where an earthquake starts
Epicenter – Point on earth’s surface directly above the focus 

3 :

Anatomy of Earthquakes 

4 :

Amount of Damage is dependant on depth
Foci is close to surface – lots of damage
Foci is far from surface – little damage – energy has to travel a long way 

5 :

Seismic waves – p 529 3 Types: P, S, and L
L waves – surface waves – roll along the earth’s surface
Body waves: P and S waves
Body waves travel faster than surface waves feel p and s waves first after an earthquake 

6 :

Body waves P wave Primary wave first to arrive
Ground squeezes and streches in the direction of wave travel
Travels through solids and liquids
S wave secondary wave second to arrive
Ground is perpendicular (90) to direction of wave travel
Travels through solids but not liquids
Another name for Swave is shear wave 

7 :

Smaller amplitude than surface (L) waves, but faster, P arrives first P and S waves 

8 :

Two Types of Surface Waves Most of the destruction
Larger amplitude than body waves 

9 :

Why do P waves reach stations before S? Outer core is Liquid – S waves can’t travel through, but p can p 530 

10 :

Surface waves L wave – Travels along the earth’s surface
Last to arrive
Ground motion is a rolling action like ripples on a pond 

11 :

Seismology Seismometers  instruments that record seismic waves
Records the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape 

12 :

A seismograph designed to record vertical ground motion The heavy mass doesn’t move much
The drum moves 

13 :

Lateral Movement Detector In reality, copper wire coils move around magnets, generating current which is recorded. 

14 :

Seismograms tell :
How long an earthquake lasted and the amount of ground shaking
Magnitude – rates the strength of an earthquake
Higher the magnitude the stronger the earthquake 

15 :

Each 1 step increase in magnitude = 10 times the size of seismic waves
Seismograms determine how fast seismic waves are travelling.
Look at p531
P waves = 5.5 min and S = 10 min 

16 :

Earthquake focus and epicenter 

17 :

Note how much bigger the surface waves are Body Waves Delay between P and S arrivals gives distance to epicenter 

18 :

Graph to find distance to epicenter 

19 :

Don’t need to know the next few slides, but it is cool to do ;) 

20 :

Locating the epicenter of an earthquake
Three seismographs needed to locate an epicenter
Each station determines the time interval between the arrival of the first P wave and the first S wave at their location
A traveltime graph then determines each station’s distance to the epicenter 

21 :

Locating Earthquake Epicenter 

22 :

Locating the epicenter of an earthquake
A circle with radius equal to distance to the epicenter is drawn around each station
The point where all three circles intersect is the earthquake epicenter 

23 :

Epicenter located using three seismographs 

24 :

Earthquake Belts
95% of energy released by earthquakes originates in narrow zones that wind around the Earth
These zones mark of edges of tectonic plates 

25 :

Locations of earthquakes from 1980 to 1990 Broad bands are subduction zone earthquakes, narrow are MOR 80% of seismic energy around Pacific Rim 
