Volcanoes Prep

This is practice for exam

How Do earthquakes happen?

• Stress buildup

• when stress> friction, there is sudden movement along the fault

• Consequently energy is released

Definition of fault

Fracture between two blocks of rock

Why do earthquakes cluster close to plate boundaries?

Plate boundaries are highly stressful environments

Where do earthquakes originate in?

Hypocenter

How many earthquakes happen every week/ month

• 100s every week

• 1,000s a month

What device is used to measure seismic activity?

Seisometer

What do X,Y,Z mean in seismic waves?

• North-South

• East-West

How do we know about the earthquake before it happens?

Different seismic waves travel at different speeds

Body waves

Travel through earths interior

Surface waves

Travel through earths surface (Causes the most destruction and move at 90%)

P-Waves

Are the fastest traveling waves( moves like slinky)

S-Waves

Travel at 60% of P waves and causes the shaking

What scale is used to measure earthquakes globally

Moment magnitude scale (Logarithmic)

What scale is qualitative

The Mercalli scale (Used to describe earthquake shake amount at specific location)

What scale was designed in CA and meant specifically for earthquakes in CA

Richter scale

How do you calculate shaking?

Subtract small from big then times X10. EX 9-6=3—> 10X10X10 = 1000

How do you calculate for energy released?

Subtract small from big then times X32. EX 9-6=3—-> 32X32X32= 32,768

Haiti, January 2010

• Magnitude 7

• 160,000 Deaths

New Zealand September 2010

• Magnitude 7.1

• 2 deaths

• Depth of hypocenter = 6 miles

New Zealand February 2011

• Magnitude 6.3

• 185 deaths, 2000 injuries

• Depth of hypocenter = 3 miles

Landslides

• Geographically limited but can cause harm and casualities

Liquefication

• Where water- saturated, unconsolidated sediments are transformed into a substance like liquid (This occured during the 2011 New Zealand earthquake)

Avalanches

• Occur when gravity overpowers strength of snow. (kills 150/yr)

Tsunamis

• are often large waves caused by earthquakes or large explosive volcanic eruption

What causes tsunamis to occur?

When a big fault ruptures on the ocean floor

Tsunami vs normal waves

• Tsunamis affect the entire water column, do not break the same

• Waves only affect the surface

Japan 11th, March 2011

• Magnitude 9.1

• Surface waves arrived after s waves

• 40 minutes to prep

Hangwall

• The rock volume above the dipping fault

Footwall

• The rock volume below the dipping fault

Subduction

• Normal

• Reverse

Continental Rift

• Normal

Oceanic Rift

• Normal

Strike Slip

• Strike slip

Continental Collision

Reverse

Chance of earthquake occuring today

100%

Nepal 2015 Earthquake

• 7.8 magnitude

• 9000 deaths

• 22000 injuries

• Continental collision = reverse

• Avalanche and landlsides

Why did the mid rise building collapse?

• Frequency of the earthquake matched the frequency of the mid rise (Mid frequency)

What happens when you increase an earthquakes wave period

• Frequency decreases

Which material has the highest earthquake frequency?

Hard bedrock

What type of building will collapse at a low frequency?

• low rise buildings

Short term

• Early warning systems (USGS)

• Earthquake education in high risk regions

Long term

• Hazard mapping (Contains intraplate seismic activity

• Engineering solutions:

  • Base isolation

  • Vibration control dampeners

  • Pendulum damping

Epicenter

Is the point on earths surface of where the earthquakes originated