7. Earthquakes and Tsunamis

Question 1

ShakeAlert

Answer 1

• warns LA residents about incoming earthquakes by tracking S-waves and surface waves

Question 2

Modifiec Mercalli Scale

Answer 2

• scale used to measure intensity of shaking in earthquakes

- 7 = something falling, people scared

Question 3

What is the ring of fire?

Answer 3

• series of oceanic trenches, volcanic arcs

- subduction zone between oceanic lithosphere and continental

Question 4

Intraplate earthquakes

Answer 4

• earthquakes happening within the tectonic plate

- Happened in early 1900s in New Madrid Seismic Zone. Aftershocks still exist today because the fault is reactivated

Question 5

What is the New Madrid Seismic Zone?

Answer 5

• Located in Missouri area
• A big intraplate earthquake happened there in early 1900s (not anywhere close to tectonic plates)
• Since then, aftershocks
• It’s a failed rift- Pangea or Rodinia tried to break it apart.
• But the scar/ fault is reactivated

Question 6

What is liquefaction?

Answer 6

• when soil turns super liquidy when water is rushed into it
• causes a bunch of damage for earthquakes
• biggest risk to structures in SF

Question 7

What are earthquakes caused by? Use focus, epicenter, body waves

Answer 7

• caused by movement in fault lines, which cause ground to shake
• focus- where earthquake starts
• epicenter- surface area above focus
• body waves (P and S) emanate seismic waves first, then surface waves follow for destruction

Question 8

Seismometer

Answer 8

Measures seismic waves of earthquakes
In ground
3 to locate them

Question 9

Moment Magnitude

Answer 9

way to measure intensity
1-10
Single change in unit means 31.6x more energy

Question 10

What is the elastic rebound theory?

Answer 10

sudden release of elastic strain on fault releases seismic energy, causing earthquakes

Question 11

DART SYSTEM

Answer 11

deep ocean assessment and reporting of tsunamis

system of buoys in pacific that measures pressure in water column, not displacement

Question 12

Can we predict when or where earthquakes will occur? How big they’ll be?

Answer 12

No. Can only assess hazard.

Question 13

What are 3 factors that govern the size of an earthquake?

Answer 13

1. Magnitude
2. Distance to surface- closer is bigger
3. Rock type- looser rock will cause more building destruction. Easier for surface waves to move through bedrock, but likely will cause less damage to buildings

Question 14

Tell me everything about tsunamis.

Answer 14

• anything that displaces ocean floor- volcanic eruption, landslide underwater, but mainly earthquakes
• rupture displaces water upwards, wave moves rapidly in ocean (500 km/ hour).
• As they approach the land, they slow down (45 km/hour) and increase in height, then it goes in.
• Waves difficult to detect: in ocean, crest of wave is only a few inches