1. Earthquakes

2. Earthquakes
When plates move very slowly and over a long period of time
Eventually a sudden shaking of the crust occurs at a particular place: Earthquake

3. Earthquakes
The majority of earthquakes occur at the boundaries of tectonic plates.
Individual earthquakes also occur where there is a fault.
A fault is a zone of weakness in the crust along which some movement of rock occurs.

4. Three Types of Faults
Reverse – compression causes horizontal and vertical movement
Normal: Tension causes horizontal and vertical movement
Strike-Slip – shear causes horizontal and vertical movement

6. Earthquake Terms
Focus: the area in the crust (below surface) where energy is released during an earthquake (where the earthquake begins)
Shallow: 0-70 km
Intermediate: km
Deep: over 300 km
Epicenter: The point on the surface directly above the focus of an earthquake

8. Process
As tectonic plates move, friction causes the rocks at plate boundaries to stretch or compress.
Like a stretched rubber band or a compressed spring, these rocks store energy called the Elastic Rebound Theory.
When the pressure builds up within the crust, the stored energy is suddenly released as the rocks slip along the fault, and an earthquake occurs.

9. Process More than ½ of all earthquakes occur along the edges of plates
Subduction zones
Mid-ocean ridge
Collision zones (continent-continent convergence)

10. Seismology The study of earthquakes
Scientists cannot predict the exact date and time of an earthquake
But… they can identify areas likely to have an earthquake in the next 10 years.

11. Seismology
A seismograph measures earthquakes, and seismologists use seismic waves to study
The energy released by an earthquake travels away from the focus in waves
Magnitude: relative size of an earthquake depends on amount energy released

12. How Seismographs Work
the pendulum remains fixed as the ground moves beneath it

14. Seismology
Seismographs show the kinds of waves, their amplitude, and the timing of the waves
Foreshocks are small tremors that precede an earthquake
Aftershocks are small tremors that follow after an earthquake

15. Scales Magnitude is expressed on the Richter Scale
Study the waves to determine the magnitude and location of the earthquake
Uses number 1 & up
Each # indicates ten times stronger than the # below
Ex: A rating of 8 has a magnitude ten times as great as an earthquake with a magnitude of 7
7 or higher indicates a major earthquake ( 10-felt all over the earth)

16. How are Earthquakes Measured? Richter Scale

17. Scales Modified Mercalli Scale: use to rate intensity
Roman numerals I to XII describes damage done by the quake
XII : total destruction
An earthquake with one magnitude, damage can vary depending on the location

18. How are Earthquakes Measured? Mercalli Intensity Scale
Click Link for Interactive Demo

19. Seismic Waves
The conversion of potential to kinetic energy results in seismic waves
Travel through the ground 20 times faster than the speed of sound
Seismic waves reach the ground at the epicenter

20. Seismic Waves Body waves – originate from the focus of the earthquake
P waves (primary waves) are compression waves that push and pull rock as they travel
Cause particles to move back & forth
Move through solids, liquids and gases
1st waves to arrive

21. Seismic Waves
S waves – (shear/ secondary waves) Body waves that have reached the surface
Cause particles to move side to side
Do not travel through liquids

22. Comparing Seismic Waves

23. Seismic Waves Surface Waves: Third & Fourth waves
Love waves & Rayleigh waves
Travel along the surface & more slowly
Cause the most damage
Love: no vertical movement of the surface
Rayleigh: both horizontal and vertical movement

25. How to determine the distance to the epicenter
Need data from three seismographic stations including the spread of S and P waves and the time between the arrival of the s and p waves.
Forecasting
Based on calculating the probability
2 factors
History of area
Rate at which strain builds up

26. Locating Earthquakes

27. Locating Earthquakes

28. Locating Earthquakes

29. Earthquake Hazards Factors that determine the severity of damage
Design of buildings
Wooden structure = less damage
2) Ground shaking
- tall building – vibrations too rapid
-short building – vibrations too slow
stories collapsed

30. Earthquake Hazards 3) Soil Fracture Sloping area = landslides
Liquefication = sand becomes liquidy due to vibrations
Soft materials amplify the motion
Hard/resistant materials lessen the motion
Causes
sinking, falling over, buildings
Underground pipes & tanks rise to the surface

31. Earthquake Hazards
4) Tsunami: A huge wave generated by an underwater earthquake or landslide
Caused by vertical motion on the ocean floor
Open ocean
Height less than 1 m
Speed km/h

32. Earthquake Hazards Shallow water
Height increases due to breakers/shallow water
Height may exceed 30 m

33. Tsunami Warning System