Week 3: Tsunamis

Tsunami is Japanese for ____ ____

Harbour wave

Tsunamis are produced by ___________________

the sudden displacement of water

Events capable of triggering tsunamis:

* earthquakes that cause uplift of the seafloor
* landslides
* volcano flank collapse
* underwater volcanic eruptions
* meteorites

Historic tsunamis

**Cause: Lisbon Earthquake, Portugal**

* (M 9.0)
* 1755
* casualties: 20,000

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**Cause: Krakatoa Volcanic Eruption**

* 1883
* casualties: 36,000

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**Cause: Sumatra Earthquake, Indonesia**

* (M 9.1)
* 2004
* casualties: 230,000

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**Cause: Tohoku Earthquake**

* (M 9.0)
* 2011
* casualties: 16,000

Earthquakes can cause tsunamis in 2 ways:

1. Displacement of the seafloor
2. By triggering a landslide that enters water

Generally an earthquake must be of at least Magnitude: __ to trigger a tsunami

7\.5

Tsunamis develop in a 4-stage process

Tsunamis 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

Stage 2:

The waves move rapidly across the open ocean

* they can reach speeds of over 500km/h

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

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The height (amplitude) of the waves is often small

(less than 1 m)

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\*Passengers on ships in the ocean rarely even notice tsunamis passing underneath them

Stage 3:

As the tsunami approaches land, the water depth decreases

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

* **a decrease in wave speed**
* **a decrease in spacing of the waves**
* **an increase in wave amplitude**

Stage 4:

As the tsunami impacts land, waves can reach heights of dozens of meters

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

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

Diagram summary of the stages:

Tsunami Event

A tsunami event consists of a series of large waves reaching shore, that can last for several hours

**Run up**

The maximum distance that the largest wave of a tsunami reaches as it travels inland

Distant Tsunami

A tsunami that travels thousands of kilometres 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 100km to 1000km from its source

local tsunami

A tsunami that affects shorelines within 100km of its source

* most dangerous
* eg. Japan

Regions at risk

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which oceans are at most risk?

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

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

Primary effects

* flooding and erosion → destroy beaches, coastal vegetation and infrastructure

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After the tsunami retreats to the ocean, scattered debris is left behind

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Most tsunami deaths are from drowning, injuries results from physical impacts from debris

* crushed

Secondary effects:

These are effects that generally occur after the event is over

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* Fires may develop due to ruptured gas lines or from ignition of flammable chemicals
* water supplies become contaminated and water- bourne diseases (cholera) may spread

Indian Ocean Tsunami of 2004

This catastrophic event occurred on Dec. 26th.

* The source was a __**M 9.1**__ earthquake of the west coast of Sumatra
* (an Island in Indonesia)
* __**3rd Strongest earthquake in world history**__
* The earthquake occurred in a __**Subduction zone**__
* 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
* The Tsunami reached nearby Indonesian islands within minutes of the earthquake
* Many costal communities in Indonesia and surrounding countries were heavily damaged by the event
* Countries bordering the Indian Ocean did not have a tsunami warning system like those bordering the Pacific Ocean
* People were caught by surprise and over 23,000 died
* Many were unfamiliar with Tsunamis
* some were even intrigued by approaching waves
* Most people were ignorant of an early warning sign
* the receding sea

Lessons from the 2004 Tsunami

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

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

Why isn’t a warning system enough by itself?

* emergency officials must have an organized plan for evacuating residents during a warning
* earthquake and tsunami education is necessary for people who live along or visit coastlines

Detecting tsunamis

The Pacific Ocean warning system uses a network of **seismograph**s to estimate earthquake magnitude.

* sensors are electronically connected to buoys verify that a tsunami was produced
* These sensors are called __***tsunameters***__

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They rest on the seafloor and measure changes in water pressure passing over them.

Structural control

Damage can be minimized through regulations on buildings and structures.

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Some cities in Hawaii require flood proofing measures such as basement window sealing and bolting homes to their foundation.

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* Concrete levees are other preventative measures but can be very expensive


* Offshore barriers are only feasible outside cities with very large populations.

Inundation Maps

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

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

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Many North American cities on the Pacific coast have such maps and development restrictions may exist there in areas at high risk of tsunamis

Land use

Vegetation plays a role in determining tsunami damage

eg.

* the Mangroves in India
* pictured in green

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In areas impacted by smaller waves, trees and dense vegetation can protect the land

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Japan Tsunami of 2011

This catastrophic event occurred on March 11th

* M 9.0
* 70km off the east coast of Japan - Local event
* A tsunami warning was issued nearly an hour before its arrival
* was a tele tsunami for California, Hawaii etc. (see image)
* Over 15,000 people died and damage to Japan’s infrastructure was extensive.

Categories of Adjustment

* Modify the loss burden
* Modify design
* modify human vulnerability

Modify the loss burden

* loss sharing
* spread the burden well beyond immediate victims

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examples:

* insurance
* relief aid

Modify design

* loss reduction
* requires a knowledge base of the hazard

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Example:

* retrofitting buildings
* diagonal beams added to old buildings for better protections
* seismic upgrade

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Modify human Vulnerability

* adjust the population to prepare to the possible events

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example:

* preparedness programs
* land use planning
* warning systems

Factors affecting adjustment choices

Hazards are not typically a priority of governments (compared to unemployment, inflation, health care, crime, poverty, etc.)

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Radical vulnerability adjustments are unrealistic (e.g., moving entire communities).

* a cost benefit assessment is typically required

Losses 1: Accepting loss

1. Accepting loss

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

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

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**example:**

* floodplain housing can be attractive because it may be inexpensive

Losses 2: sharing loss

2. Sharing loss

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This is the government-action response.

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

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

Sharing loss

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

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**Problems with Sharing Loss:**

* a disaster of sudden onset is likely to draw more money than another similarly serious disaster
* **donor fatigue** can set in if there are many disasters
* recovery can take a very long time in some countries
* aid enthusiasm to donate eventually wanes

Model of disaster recovery

4 waves:


1. emergency
2. restoration
3. reconstruction 1
4. reconstruction 2

Perception of Hazard Frequency

Assuming that adjustment to a hazard is related to the perception of the hazard frequency, what do you feel is the probability
(0.0 = 0% chance and 1.0 = 100% chance)
of each of the following hazards occurring at some point here in London over the next 50 years?

* tornado
* hurricane
* flood
* ice storm
* blizzard

Factors affecting individual adjustment choices

__**Experience**__

* more experience with a hazard results in more likelihood of adjustment

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__**Material wealth**__

* more resources results in more information and more options

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__**personality**__

* some people are more likely to take risks. Some people have more confidence than others

Prospect Theory

In each example, which option do you prefer?

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1. \
a) 1% chance of gaining $1000

b) 99% chance of gaining $100

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2. \
a) 1% chance of losing $1000

b) 99% chance of losing $1000

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Generally, people are more willing to protect against a loss than they are willing to gamble on an equilivant gain

* we place a low value on any type of loss
* see diagram:
* curve is more steep on loss side

Cultural adjustment

This type of adjustment may result from changes in an environment

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example:

* Mackenzie River Delta
* the discovery of oil forced the local communities to adjust as the resource was developed

Purposeful Adjustment

This is an adjustment that is specifically designed to reduce loss or damage

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example:

* Designing buildings to withstand earthquakes in high risk areas

Incidental adjustment

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

example:

* advances in technology have improved warning systems

Absorptive Capacity

This is a measure of the ability of people to sustain impacts from a hazard.

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It results from combinations of cultural, purposeful, and incidental adjustments.

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Example:

* In parts of Kenya, maize, beans, peas, sorghum, and ground nuts are all planted together
* This encourages deep roots among the plants, which results in a more drought resistant crop yield

Cognitive influences on Choice

Based on 100 years of past data, the estimated probability of a 100-year tornado touching down in Disastertown in 2022 was 0.01.

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In 2022 a tornado touched down in Disastertown.

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The likelihood of a 100-year tornado touching down in 2023 is considerably less than 0.01 because one struck in 2022. 

True or False?

* false
* the events are disjointed or exclusive

Gambler’s Fallacy

The belief that the occurrence of a chance event influences the probability of future occurrences

eg.

* the chance of a ball landed on 25 is the same on every spin

Theory of choice

Based on the information, would you choose to evacuate or remain?

scenario probability

0 = worst

2 = best

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1. take probability and multiply by original number
2. add up the numbers in the column
3. the highest number is the action you should take

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\*this will be a question on the midterm

* check camera roll for another example

Expected Utility

optimize the values

* choose on the basis of all expected outcomes
* the probabilities are multiplied against assessments of value
* the probabilities are multipled against assessments of value

Potential issue:

Ascribing probabilities to events usually involves uncertainty