Tsunami Hazards Flashcards
(44 cards)
What can tsunamis originate from?
Displacement of the water column by:
- Earthquakes
- Slope failure/ mass movements
- Volcanic activity
- Bolide impact
What do all tsunami sources have in common?
short lived water displacement disrupting the whole water body
What is the theory behind tsunamis?
Initial displacement - (water coloumn raised, gravitational spread of disturbance)
What is the period of a tsunami?
T - time for one wave to pass a point
How is tsunami velocity calculated?
Wavelength / time
What will the disturbance from tsunamis produce?
A wave-train of multiple waves
How will tsunami waves tend to behave? (particularly sesimogenic)
Shallow-water waves (due to the length to depth ratio)
What will the length of tsunamis typically be?
~200km
What will the typical period of a tsunami wave be?
10s of minutes
What will the amplitude of tsunami waves be in open ocean?
relativeky low (e.g 1m) compared to run up amplitude
How is the velocity for shallow water waves (tsunami) calculated?
sqaure root of gravity X depth
What is the energy loss if tsunami waves proportional to?
Wavelength - longer wavelengths more effieicnt so less energy loss leading to greater diatance travelled
What happens to tsunami waves when water gets shallower?
Velocity decreases but wave period stays constant so shorter wavelength and higher amplitude
Known as Shoaling or Amplification shorewards
Can wave speed by outrun on land?
Wave still approach rapidly at a speed too fast to outrun
What will the slope of a tsunami wave be like and how does this affect its appearance?
Still relatively gentle with wavelength of several km looks like a rapidly rising wave level instead of wall of water
How will the tsunami behave based on the displcement at fault?
Side which moved up will be peak followed by trough and side which moved down will be trough followed by peak
Thailand 04 water receded first but sri lanka had no warning
What was the ffect of the tsunami travelling across the indian ocean from sumatra 04?
Travelling through deeper ocean lead to increased wavelength
Wjat are the 5 main approaches of tsunami mitigation?
- Direct warning/ monitoring
- Planning - tsunami models
- Education and awareness
- Learning from past events
- Direct protection
What was learnt for monitoring and warning post sumatra 2004?
Lack of Indian ocean wanring system (affetcing those whose didnt feel EQ)
Lack of public awarenss due to limited EQ activity/ tsunami in recent history
What is an example of a real time monitoring system for tsunamis?
DART - direct detection and warning system
Why are DART systems important?
Provide data to warn public
Accurate warning (minimise false alarms)
Direclty feed to real time models
But with time taken to recove data and then transmit to national and local scale wave might have alrady reached shore
How does the DART system work?
Presseure sensor on the sea floor which communictes the passage of a tsunami to a buoy
Not affected by normal storm waves
Where are DART systems usually placed?
On the oceanward side of faults to provide warning for areas with time to plan
What is the assumed idea for people thinking to reach safety form tsunami locally?
Will feel EQ and head to higher ground
