Lecture 3- Tsunamis; Models of Human Response

How are tsunamis produced?

they are produced by sudden displacement of water

Tsunami is Japanese for what?

“Harbour wave"“

Events capable of triggering tsunamis:

- earthquakes that cause uplift of the seafloor

- landslides

- volcano flank collapse

- underwater volcanic eruptions

- meteorites

Earthquakes can cause tsunamis in 2 ways:

-by displacement of the seafloor

-by triggering a landslide that enters water

What must the magnitude of an earthquake be to trigger a tsunami?

M 7.5

Why don't we see tsunamis in the Atlantic Ocean?

because the plates are spreading plates here (diverging)

Tsunami Development (Stage 1)

-Displacement of the seafloor sets waves in motion that transmit energy upward and outward

-When the waves reach the surface of the water they spread outward

Tsunami Development (Stage 2)

-The waves move rapidly across the open ocean (they can reach speeds of over 500 km/h)

-The spacing of the wave crests is very large (it can be more than 100km)

-The height (amplitude) of the waves is often small (less than 1 m)

-Passengers on ships in the ocean rarely notice tsunamis passing beneath them

Tsunami Development (Stage 3)

As the tsunami approaches land, the water depth decreases

This results in the water 'piling up' and causes these effects:

-A decrease in wave speed

-A decrease in the spacing of the waves

-An increase in wave amplitude

Tsunami Development (Stage 4)

-As the tsunami impacts land, waves can reach up to dozens of metres

-The wave speed at this time can be up to 50km/h making them impossible to outrun

-During some tsunamis, the water first recedes from the shore and exposes the seafloor

Explain the earthquake-triggered tsunami development

1) Uplift water

2) Move across

3) Sea floor rising (increase in height)

4) Destroying

What does a tsunami event consist of?

a series of large waves reaching shore that can last for several hours

What is the run-up of a tsunami?

The maximum vertical distance that the largest wave of a tsunami reaches as it travels inland (elevation)

Distant Tsunami

- travels thousands of km across the open ocean

-on remote shorelines across the ocean, reduced energy lessens its impact

-also called tele-tsunamis

Regional Tsunami

A tsunami that affects shorelines 100 km to 1000 km from its source.

Local Tsunami

it affects shorelines within 100km of the source (most dangerous type)

What regions are at most risk of tsunamis?

-Coasts located near subduction zones or across oceans from subduction zones are most at risk

-Areas at greatest risk are the Pacific Ocean and the Mediterranean Sea

Primary Effects of Tsunamis

Flooding and erosion destroy beaches, coastal vegetation and infrastructure

Scattered debris is left behind

Most deaths are from drowning, injuries —> physical impacts with debris

Secondary Effects of Tsunamis

fires (ruptures gas lines, flammable chemicals), contaminated water supplies, and water-borne diseases (cholera) (occur after the event is over)

Indian Ocean Tsunami 2004

-Magnitude 9.1 earthquake to start (Sumatra, island in Indonesia)

-3rd strongest earthquake in history

-occurred in a subduction zone between Burma and the Indian-Australian plates

-Indonesia it was a local tsunami for African countries it was a tele-tsunami

-No tsunami warning system in place

-230,000 people died

Explain the Burma and Indian-Australian plates

These plates had been locked for over 150 years thus allowing strain to build

The rupture caused some land areas along the coastline to subside below sea level - land shrinks

Lessons from the 2004 Tsunami

• Effective tsunami warning systems are needed around all oceans where tsunamis can occur

• In 2006 a new warning system became operational in the Indian Ocean

• Also need an evacuation plan

• Education about tsunamis

Tele-Tsunami

On remote shorelines across the ocean, reduced energy lessens its impact (come from distant tsumanis)

What are tsunameters?

- sensors electronically connected to buoys that verify if a tsunami was produced

- they rest on the seafloor and measure changes in water pressure passing over them

-network of seismographs to estimate earthquake magnitude

Explain structural control for damage

• Concrete levees can be expensive

• Offshore barriers are only feasible outside cities with very large populations

Indundation Maps

Maps showing the geographic area that can be potentially impacted by tsunamis are created to help plan for future events

Historical records. geologic data, and aerial photography aid in making the maps

What vegetation can stop water from getting past it?

mangroves

In areas impacted by smaller waves what does vegetation do?

trees and dense vegetation protect areas further inland

Japan Tsunami 2011

-source was a M 9.0 earthquake 70km off the east coast of Japan

-A tsunami warning was issued nearly an hour before its arrival

-Over 15,000 people died and damage to Japan's infrastructure was extensive

What are the 3 Categories of Adjustment?

1) modify the loss burden (loss sharing)

- ex. insurance, relief aid

2) modify design (loss reduction)

- ex. retrofitting buildings

3) modify human vulnerability

- ex. warning systems, land use planning

What are the factors affecting adjustment choices?

• Hazards are not typically a priority of governments

• Radical vulnerability adjustments are unrealistic (moving entire communities)

• A cost-benefit assessment is typically required

Accepting the Loss

This is the 'free' choice. It is a no-action response.

People choose to live how they want regardless of the hazard risk but aid may not be provided after a disaster.

Example: floodplain housing can be attractive because it may be inexpensive

Sharing the Loss

This is the government-action response.

There may be laws in place preventing people from living in certain areas.

If governments do not intervene after a disaster, there are often political ramifications.

Aid can come from external sources (UNICEF), internal sources (government), inter-community sources (local), and insurance

What are the Problems with Sharing the Loss?

-A disaster of sudden onset is likely to draw more money than another similarly serious disaster

-Recovery can take a very long time in some countries

-Donor fatigue can set in if there are many disasters

-Aid and enthusiasm to donate eventually wanes

What are the factors affecting Individual adjustment choices?

Experience, material wealth, personality

What is prosepct theory?

-people are more willing to protect against a loss than willing to gamble on an equivalent gain

-People feel strongly about losing anything they own

-People are more likely to throw out the chances of winning

What are the 4 human responses to hazards?

1) Cultural Adjustment

2) Purposeful Adjustment

3) Incidental Adjustment

4) Absorptive Capacity

What is Cultural Adjustment?

-This type of adjustment may result from changes in an environment

Example: Mackenzie River Delta

-The discovery of oil forced the local communities to adjust as the resource was developed

What is Pursposeful Adjustment?

-specifically designed to reduce loss or damage

Example: designing buildings to withstand earthquakes in high-risk areas

-If building is designed to sway less chance it will collapse during an earthquake

What is Incident Adjustment?

not primarily hazard-related, but they have the effect of reducing potential loss

Example: advances in technology have improved warning systems

What is Absorptive Capacity?

-measure of the ability of people to sustain impacts from a hazard (combination of all adjustments above)

-it's a combination of cultural, purposeful and incidental adjustments

-Example: In parts of Kenya maize, beans, peas, sorghum, and ground nuts are planted all together (encourages plants to fight for resources, only the strongest of plants will survive - a more drought resistant crop yield)

What is the gambler's fallacy?

the belief that occurence of a chance event influences the probability of future occurences (not true)

What is Expected Utility, and what is a potential issue with using it?

Expected Utility helps optimize decisions by considering all possible outcomes, multiplying probabilities by their assessed values.

A key issue is that assigning probabilities to events often involves uncertainty