Waves 3

Question 1

What is a tsunami?

Answer 1

rapid displacement of large amounts of ocean water when hit with massive jolt of energy

• ex/ sudden vertical change in a seafloor fault

Question 2

Tsunami can be caused by what events?

Answer 2

1. Earthquakes
   - MOST often
   - vertical displacement of sea floor
2. Volcanic eruptions
3. Landslides
4. Meteor impacts
   - potentially the BIGGEST
5. Icebergs from glaciers
   -> usually SMALLEST

Question 3

What does the energy released by a seismic vertical motion do?

Answer 3

1. flows away radially from point source
2. propagates as wave train
3. disturbs ENTIRE water column

Question 4

What type of waves are tsunamis?

Answer 4

shallow water waves
ALWAYS

Question 5

tsunami in the open ocean have large ___ and small ___

Answer 5

Large wavelengths (200-400km) and periods (1hr)
Small wave height (< 1m) and steepness (&laquo_space;1)

Question 6

The period of a tsunami in open ocean is about

Answer 6

~ 10min to 1 hr

Question 7

The wave speed of a tsunami in open ocean is

Answer 7

very fast, determined by depth
(average ocean depth is ~4500m)
(average speed 210m/s or 750km/hr)

Question 8

What is the average ocean depth?

Answer 8

~4500m

Question 9

True or False: All tsunami waves cross a given part of the ocean at the same speed

Answer 9

True
- speed depends on water depth

Question 10

do tsunami waves break?

Answer 10

Not really
- def not in open ocean
- at coast, break at about 1m depth
- typically approach shore as an onrushing flood/surge for minutes

Question 11

Can we outrun a tsunami?

Answer 11

no :(

Question 12

As a tsunami reaches the shore, wave height could increase up to

Answer 12

30m
depending on shape of harbour

Question 13

What’s the tsunami capital of US

Answer 13

Hilo, Hawaii

Question 14

Why are tsunamis devastating in some semi-enclosed bays? What was an example of this?

Answer 14

due to resonance
ex/ Hilo Bay

Worsened because the tsunami wave period was a multiple of the basin’s natural resonant period…

Question 15

What was the deadliest Tsunami in human history? (When, cause, deaths)

Answer 15

Indian Ocean Tsunami
Dec 2004

cause: M9 Subduction Zone Earthquake
deaths: > 200,000

Question 16

Where do most tsunamis occur?

Answer 16

Ring of Fire in the Pacific Ocean
(Japan, Alaska, Chile, Indonesia, etc)

Question 17

What kind of submarine earthquakes is needed to generate tsunamis?

Answer 17

Ones that create vertical motion

ex/ reverse faults, plates moving over one another, ruptured sea floor

Question 18

Will a tsunami be created by slip earthquakes?

Answer 18

unlikely, two plates sliding past each other does not create vertical motion

Question 19

How can volcanoes cause tsunamis?

Answer 19

land: dump mass into ocean
water: displace water when ejecting gas/lava

Question 20

the ideal location for tsunami generation are ___ zones

Answer 20

subduction

Question 21

Will we experience the crest or trough first?

Answer 21

Depends where you are relative to where tsunami is generated

Question 22

Most recent Cascadia mega thrust quake

Answer 22

January 1700

Question 23

What subduction zone is closest to us?

Answer 23

Cascadia

Question 24

When a receding of water is observed, how long do we have before the tsunami (from Cascadian subduction zone) hits?

Answer 24

15-30 mins

Question 25

How can we predict arrival time?

Answer 25

predict from celerity

= distance / ( 3.1 √depth )

Question 26

How many tsunami warning centres do we currently have?

Answer 26

2
(PTWC) Pacific Ocean and Alaska (WC/ATWC)

Question 27

Tsunami watch vs Tsunami warning

Answer 27

watch
- not confirmed, “might occur”

warning
- detected by buoys & tidal gauges, “have occurred”

Question 28

What is the DART Buoy system?

Answer 28

Deep Ocean Assessment and Reporting of Tsunami
- measures pressure changes on seafloor caused by tsunami
- verify existence and tells warning centers

Question 29

Describe how the DART Buoy system works

Answer 29

Tsunameter
- pressure sensor on ocean floor
-> can feel passing tsunami at bottom cuz they’re shallow waves!

Surface Buoy
- relays signal to PTWC via satellite

Question 30

How many DART Buoys are there in world oceans

Answer 30

50

Question 31

How to survive a tsunami

Answer 31

• natural warnings: receding water, strong earthquake
• listen to official warnings
• move boats into open ocean
• head to high ground
• animal behaviour

Question 32

True or False: in the case of a tsunami warning, we should move boats even further into the ocean

Answer 32

true
open ocean is safe !