Tsunamis

Question 1

Give an overview of the Tohoku Earthquake

Answer 1

11/3/2011
moment magnitude of 9.0
32km depth 
subducting plates - pacific thrust below N.American
plate bends about 15 degrees here

Question 2

what are the earthquake waves?

Answer 2

surface waves are the most destructive (these are S waves that make it to the surface)
compression waves (P-waves)
surface waves
- rayleigh waves - particle motion is up and down
- love wave - particle motion is side to side.
Time between P (primary) and S (secondary) waves can be used as an early warning

Question 3

Propogation - describe the wave terminology

Answer 3

Wave height is the distance between the crest and the trough.
Crest - the top of wave
Trough - dipped wave
Wavelength - distance between two crests
typical tsunami wavelength is 100-300km

Question 4

what is water depth (D) in deep ocean?

Answer 4

approximately 2-4km
in deep ocean waves follow shallow water theory.
EQ generated tsunamis follow shallow-water theory in deep ocean as depth (couple km) is much less than tsunami wave wavelength (hundreds of km)

Question 5

what is the deep water theory?

Answer 5

D > wavelength/2

Question 6

What is the shallow water theory?

Answer 6

D

Question 7

what is the shallow wave theory?

Answer 7

c = celerity of wave (speed)

= square root of g x D

Question 8

what does a tsunamis celerity in the deep ocean depend on?

Answer 8

depends on just gravity (g = approx 10ms-2) and water depth (D)

Question 9

what are the differences between deep and shallow water?

Answer 9

deep ocean: shallow wave theory, whole water column affected, little loss of energy, long wave periods (mins)
Shallow ocean: waves slow down, conservation of mass, wave height increase, become nonlinear

Question 10

what is the use of knowing velocity?

Answer 10

know how log it will take to reach other continents

Question 11

describe DART system

Answer 11

seafloor bottom pressure recording system, requires money ad maintenance by different governments

Question 12

Land

what is wave refraction?

Answer 12

orthogonal lines denote areas of equal wave energy, wave energy is concentrated at headlands and dispersed in bays

Question 13

Land

what is run-up?

Answer 13

the difference between elevation of maximum tsunami penetration (inundation line - how far water goes inland) and sea level at time of tsunami

aka: how high does the wave get above normal sea level.

Question 14

Land

What is drawback?

Answer 14

sudden appearing to drain away of the ocean or withdrawal of water line from shore line. this is the trough of the tsunami reaching the shore, it doesn’t always happen.

Question 15

are EQs spatially related?

Answer 15

NO, can cause aftershocks and shift stress but one earthquake cannot cause another

Question 16

are big EQs increasing in time?

Answer 16

NO

Question 17

does the full moon affect tsunamis?

Answer 17

NO