1. Earthquakes, Volcanoes and Severe Weather
Natural Hazards
Earthquakes, Volcanoes and Severe Weather

2. What is an earthquake?
When the stress built up between two blocks of crust over comes friction, an earthquake occurs
While stress is being “built up,” this is stored elastic energy
When the earthquake occurs, the elastic energy is converted into mechanical energy
Focus
Epicenter
Seismic Waves

3. Seismic Waves P waves S waves Surface waves Primary waves
First to arrive, move fastest
Compression waves
Feels like a punch or jolt upwards
S waves
Secondary waves
Arrive second
Longitudinal waves
Shake back and forth
Surface waves
Move the slowest, arrive last
Make the ground move like ocean waves
Often causes the most destruction

5. How do we detect earthquakes?
Devices called seismographs detect shaking
Larger amplitude means larger earthquake

7. How do we know how big it was?
Magnitude- unit of measurement for earthquakes
Different Scales
Mercalli
Based on amount of damage
Richter
Based on the earthquake’s size
Accurate for small earthquakes nearby
Different depending on distance from epicenter
Moment Magnitude
Measures the total energy released by an earthquake
Most accurate
Used by scientists today

8. Magnitude
2.5 or less
Usually not felt, but can be recorded by seismograph.
2.5 to 5.4
Often felt, but only causes minor damage.
5.5 to 6.0
Slight damage to buildings and other structures.
6.1 to 6.9
May cause a lot of damage in very populated areas.
7.0 to 7.9
Major earthquake. Serious damage.
8.0 or greater
Great earthquake. Can totally destroy communities near the epicenter.

9. How do we know where the epicenter is?
Location:
Triangulation
We know how fast different waves move, so we can calculate how far away the earthquake was by the amount of time between arrival of P waves and S waves
We use at least 3 locations to find the location of the quake

10. Triangulation Practice

11. Earthquake Hazards Ground shaking Surface rupture Landslides/rock fall
Causes damage to structures
Surface rupture
Offset of the ground surface
Landslides/rock fall
Occurs on steep slopes (M4.0 and larger)
Shaking causes hillside to break loose
Flooding
Due to broken pipes, failed dams, or result of tsunami or seiche
Fire
Usually caused by ruptured gas lines or arcing power lines
Ground shaking
Surface rupture
Landslides/rock fall
Flooding
Fire
Tsunami/Seiche
Liquefaction

12. Seiche and Tsunami
Seiche: standing wave in an enclosed or partially enclosed body of water
Tsunami: a wave train, or series of waves, generated in a body of water by a disturbance that moves the whole water column

13. Liquefaction
Liquefaction is the mixing of sand or soil and groundwater during the shaking of a moderate or strong earthquake. When the water and soil are mixed, the ground becomes very soft and acts similar to quicksand.

14. Wasatch Fault
One of the longest and most active normal faults in the world, the 240-mile-long Wasatch fault extends from Malad City, Idaho, south to Fayette, Utah.
It is subdivided into 10 segments, averaging 25 miles in length
Segments rupture independently
Nearly 80% of Utah’s population lives within 15 miles of the Wasatch Fault

17. https://earthquake.usgs.gov/hazards/qfaults/map/#qfaults
f_se#executive

18. Preparation df

19. Volcanoes Volcanoes can occur at three types of locations:
Diverging Boundaries
Mid-ocean ridges
Converging Boundaries
Island arcs- Japan, New Zealand, Aleutian Islands
Oceanic-Continental collision: Andes Mountains, Cascade Mountains (Mount St. Helens)
Hotspots
An extra hot plume from the mantle causes melting and magma to build and erupt in a mostly stationary location
Hawaii
Yellowstone

21. Magma Viscosity- the resistance of a liquid to flow
High: gloopy
Low: runny
Silica- particles made of silicon, most abundant material in Earth’s crust
Makes magma more viscous
Carbon dioxide- dissolved in magma (like soda)
Causes magma to rise and erupt

22. Types of Eruptions Energy Transfer- Heat to Mechanical Quiet Explosive
Low silica= low viscosity
Lava pours from the vent or cracks
Example: Hawaii
Explosive
High silica= high viscosity
Builds up in the volcano’s pipe and builds pressure
When pressure is released, trapped gasses rush out, causing a violent eruption
Example: Mount St. Helens

23. Volcanic Hazards Lava Flow Pyroclastic flow “Bombs” and rock fragments
Ash fall/acid rain
Landslide
Mud/debris flow
Fumaroles/ volcanic gases

24. Severe Weather Thunderstorms Tornadoes Hurricanes Blizzards Floods
US Deaths Due to Severe Weather

25. Predictability Time Location Magnitude Time: Location: Magnitude:
Some hazards are proceeded by “warning signals”
Location:
Hazards require certain criteria to occur
Magnitude:
Based off previous events and data for current situation