Week 5 Flashcards

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1
Q

What are Tsunamis

A

Tsu - Habor
Nami - Wave

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2
Q

What is the important distinction between normal ocean waves and tsunami

A
  • Wave length
  • Wind driven waves have short wavelength (tens of meters)
  • Tsunami waves lengths are long (up to more than a hundred kilometers)
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3
Q

Initiation of a Tsunami

A
  • reverse faults are responsible for earthquake included tsunami by uplifting/ subsiding a large area of the sea floor
  • tsunami waves propagate away from the source
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4
Q

Two fundamental physical parameters of water waves

A
  1. Wavelength (distance from peak to peak)
  2. Period (time for passage of one wave)
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5
Q

Tsunami propagation speed

A

As it enters shallow water, tsunami waves speed will slows and its height increases creating destructive, life threatening waves

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6
Q

What are the causes of tsunamis

A
  1. Undersea rupture of normal, thrust, megathrust faults
  2. Undersea landslide
  3. Undersea volcanic eruptions
  4. Asteroids
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7
Q

How do we calculate velocity of the tsunami

A

velocity = sqr (gravity x water depth)

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8
Q

Undersea rupture of normal, thrust, megathrust faults

A
  • if the rupture is 100 km wide, so is the initial tsunami wavelength
  • the waves get steeper and higher as they come into shallower and shallower water
  • often become a chaotic front
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9
Q

Example of Undersea rupture of normal, thrust and megathrust faults

A
  1. 2004 Indian Ocean and 2011 Tohoku
  2. 1933 Sanriku (normal fault)
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10
Q

Factors affecting height of tsunami waves

A
  1. earthquake magnitude
  2. area of rupture zone
  3. rate and volume of water displaced
  4. sense of ocean floor motion
  5. depth of water above rupture
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11
Q

Undersea landslides

A
  • tsunami from fast moving landslides or rock falls can displace immense amounts of water and generate tsunami
  • the height of fall has more effect than volume of mass that displaces water
  • heavily dependent on the speed and volume of the landslide
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12
Q

Examples of undersea landslides

A
  • 1958 Lituya bay
  • Hawaiian islands
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13
Q

Tsunami generate by volcanic eruptions

A
  • volcanic processes can displace large volumes of water and trigger tsunami:
    1. fast-moving flows of hot volcanic ash
    2. submarine volcanic explosions
    3. collapse of volcano in giant landslide
  • tsunami generated by volcanic eruptions are poorly understood; maximum in size unknown
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14
Q

Examples of undersea volcanic eruptions

A
  • 1883 Krakatau
  • 1628 BC Santorini
  • 2022 Tonga Eruption
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15
Q

Three plausible causes (1883 Krakatau eruption)

A
  • an enormous explosion displaces large quantities of seawater
  • the underwater portions of the volcano subside quickly during the eruption, greatly disturbing the seafloor
  • large volumes of volcanic material enter the sea and displace sea water
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16
Q

The cause of 2022 tonga

A

atmospheric air pressure waves

17
Q

Asteroids

A
  • a 10 km diameter meteorite struck earth 65 million years ago and led to the extinction of about 50% of known species at the time. Clear geological evidence for an immense tsunami on the coasts of the gulf of Mexico
  • frequency of impact low - 1km asteroid impact once every million yrs
18
Q

Simulation of when 1km asteroid falls into 5 km deep ocean

A
  • generate 3 km deep cavity in the sea floor
  • cavity walls would collapse rapidly and generate tsunami
  • kilometer high tsunami waves would cause immense run up on shore
  • waves would decrease in size fairly rapidly from impact site
19
Q

Tsunami from landslides, rockfalls and meteorites

A
  • can displace immense amounts of water and generate a tsunami
  • height of fall has more effect than volume of mass that displaces water
  • the speed of meteorites plays the most important role in generating tsunami
20
Q

Tsunami Hazard Mitigation

A
  • land use zoning: limit buildings to elevation above those potentially flooded
  • structures to resist wave erosion and scour
  • orient streets and buildings perpendicular to wave crest
  • well-rooted tress can slow wave
  • large ditch or reinforced concrete wall can reduce impact of first wave
21
Q

Tsunami warnings

A
  • Warning systems now perfected for far-field (far from the source) tsunami
  • Pacific ocean tsunami warning network monitors large earthquakes and ocean waves and transmits warnings to 26 countries. Travel time for tsunami is accurately calculated and ocean surface height are detected from readings of tidal sensors and ocean bottom sensors
22
Q

Adaption to tsunami hazards

A
  • buoys near the anticipated sources of tsunami detect a tsunami in its early stages and transmit to the RTWC in Hawaii
  • Tsunami warning systems give warning of an hour to a day
  • Tsunami- resistant buildings
  • Warning signs
  • Vertical evacuation structures