Introduction to earthquakes and related hazards Flashcards
How do Tsunami waves form?
Subudction induced earthquake under the sea causes energy release into the sea
High energy waves slow doen as they approch the shore
But they do increase in height
How do tsunamis affect peoples livelihoods?
Huge infiltration of saltwater damages crops
Takes a long time for ground to recover
Causing long term/permanent displacement
Why are the impact of tsunamis so significant?
Effects can be far reaching relative to the location/source
What is the typical speed of a tsunami wave in deep water?
200 m/s
Can tsunamis be predicted?
Prediction is possible for distal locations e.g. Pacific Tsunami Warning centre
Improved technology and modelling techniques advance prediction of wave heights
Where do the largest earthqaules normally occur?
Subduction zones
Like the ones in the Pacific ring of fire
What is the equation to work out seismic moment (magnitude)?
Slip of fault * area of fault plane
Why are volcanic earthquakes smaller than tectonic ones?
They involve a lot less energy
What are some examples of anthropogenic produced seismic events?
Explosions and seismic surveys
Heavy traffic
Reservoir and fluid injeection induced earthquakes
Mining-induced earthquakes
What is the definition of an earthquake?
The release of accumulated elastic strain, causing a rupture of rock along a fault
What is the definition of the epicentre?
The location on the earth’s surface above the focus of the earthquake where the energy is released first
What is the definition of strain?
Measure of the amount of deformation that the rock has experienced
What is the definition of stress?
The force acting (per unit area) on any defined plane within the volume of rock
What is the depth of a shallow earthquake (most damaging)?
0-70km
What is the depth of intermediate earthquake?
70-300km
What is the depth of a deep earthquake
300-700km
Why is understanding seismic hazard important?
Know where the fault lines are in relation to the population density
Know the strength of the infrastructure
Why is understanding the earth structure important?
Seismic waves can be recorded in different part od the world
Understanding signal and time it takes to receive signal means we learn more about the interior structure of the earth
How many large (over magnitude 8) earthquakes occur every year?
About 1
How many very small (slightly felt) earthquakes occur every year?
300,000
On average, how many people die every year due to earthquakes?
10,000
But this is not consistent, depends if/when large eruptions occur and their secondary hazards
Give some example of secondary natural hazards
Ground shaking
Ground failure/movement
Landslides
Avalanches
Mudflows
Liquefactions
Subsidence
Tsunamis
Give some examples of anthropogenic hazards (hazards to people, due to human infrastructure)
Damage/collapse of buildings or bridges
Floods from dam failures and water pipelines breaking
Falling objects e.g. cables
Disruption of transportation, communication, power, water supply, and sewage systems
Radioactive leaks from nuclear reactors, power stations
How do you determine earthquake potential?
Instruments e.g. seismology
Historic records e.g. paleoseismology- earthquake records
Sedimentary records
Predictive probability based on past patterns
