Lecture 12

Question 1

Tsunami

Answer 1

A body wave generated in an ocean or large lake by seismic activity.
Long wavelength (often >100km)
High speeds (>800 km/h)
Amplitudes of ~10cm until approach continental shelf (>10m)
Distinguished from regular ocean waves by long wavelength
Period is long enough that loss of energy due to viscous dampening is minimal (even over long distances)

Question 2

Displacement wave

Answer 2

Waves in an ocean or lake that result from a displacement of water caused by shifts in the basin floor or movement of material into the water (such as a rock avalanche). They may be seismogenic

Question 3

Ways to generate a tsunami (5)

Answer 3

1) Rapid tectonic strain of the sea floor during an earthquake with significant vertical component (> 1 m) over a large area (hundreds of km2)
2) Submarine landslide
3) Subaerial landslide
4) Submarine volcanic eruption
5) Meteorite impact

Question 4

1929 grandbanks EQ and tsunami

Answer 4

Most deadly EQ and tsunami in Canada
2.5 hours after EQ, tsunami strikes southern end of Burin Peninsula in NFLD
3 main pulses
28 lives

Question 5

Depth

Answer 5

1/2 wavelength

Question 6

Crest

Answer 6

Amplitude of wave over sea level

Question 7

Trough

Answer 7

Amplitude of wave under sea level

Question 8

Wavelength

Answer 8

Distance from a crest to next crest, or distance from trough to next trough

Question 9

Amplitude

Answer 9

Difference from sea level wave rises or falls

Question 10

Height of displacement wave if caused by subaerial or submarine landslides

Answer 10

May be greater than 100m

Question 11

Wavelength of displacement wave caused by seismicity

Answer 11

Can be 1000s of metres

Question 12

Tidal waves

Answer 12

Waves resulting from the gravitational force between Earth and the Moon or Sun. Have a period of two waves per day (semi-diurnal)
Water is not being displaced, but pulled

Question 13

Other ocean waves

Answer 13

For example from storm surges

Lower heights and shorter periods

Question 14

Wave generated by wind (period, wavelength, height on sea)

Answer 14

Period: 1-25s
Wavelength: 1-1000m
Height on sea (2xA): < 3m

Question 15

Wave generated by tsunami (period, wavelength, height on sea)

Answer 15

Period: 10-60 min
Wavelength: >100km
Height on sea (2xA): <1m

Question 16

Celerity

Answer 16

Wave speed

Question 17

Celerity equation in shallow water

Answer 17

Where d/L is <0.05
sqrt(gD)
g: 10m/s^2
D: depth (m)

Question 18

Shoaling

Answer 18

As wave approaches decreasing water depths the leading wave will slow, but the water behind it will “build up”an increase the wave height

Question 19

Focusing

Answer 19

As a wave enters a concave bathymetry, the wave front bends due to refraction of the waves, and they converge onto each other

Question 20

Resonance

Answer 20

As a wave enters a closed bay, waves will reflect and oscillate in the bay. If the period of the oscillation is in phase with the tsunami wave, then a larger amplitude will result, similar to a standing wave

Question 21

What causes amplification?

Answer 21

Shoaling
Focusing
Resonance

Question 22

Wave energy loss

Answer 22

Inversely proportional to wavelength

Tsunamis have long wavelengths so maintain energy over long distances

Question 23

Tsunami monitoring

Answer 23

Buoy warning systems

Deep Ocean Assessment and Reporting of Tsunami (DART)

Question 24

Run-up heights

Answer 24

Maximum height reached on land

Can be determined through deposits

Question 25

Inundation distances

Answer 25

How far inland

Can be determined through deposits

Question 26

Tsunami prediction

Answer 26

Models

Historical examples