Seismic Hazards Flashcards
What are tsunamis?
Giant sea waves
What are tsunamis generated by?
Shallow-focus underwater earthquakes, violent volcanic eruptions, underwater debris slides and landslides into the sea.
What is an earthquake?
A shaking motion caused by pressure release.
What is the focus?
The point at which the pressure is released within the crust.
What is the epicentre?
The point immediately above the focus on the earth’s surface.
What are the three types of earthquakes?
Shallow focus
Intermediate focus
Deep focus
How deep is a shallow focus?
Up to 70km deep
How deep is an intermediate focus?
70-300km deep
How deep is a deep focus?
300-700km deep
Which type of earthquake tends to cause the greatest damage?
Shallow focus earthquakes tend to cause the most damage.
Where do the vast majority of earthquakes occur?
Along plate boundaries
At which plate boundary are the most powerful earthquakes associated with?
Destructive
Why do earthquakes occur at conservative plate boundaries?
Movement along the fault line causes an earthquake.
Give an example of a famous fault line
San Andreas Fault, California
The San Andreas Fault is the boundary for which two plates?
North American
Pacific
What are earthquakes that do not occur at plate boundaries associated with?
The reactivation of old fault lines.
Give an example of an earthquake that occurred away from a plate boundary
UK Midlands
When was the UK Midlands earthquake?
September 2002
What was the magnitude of the UK Midlands earthquake?
4.8 Richter
Where was the epicentre of the UK Midlands earthquake?
Dudley, west of Birmingham
Which old fault line is believed to be responsible for the UK Midlands earthquake?
Malvern lineament
What type of activity could be a cause of earthquakes?
Human activity
Which types of human activity could be responsible for human activity?
Building of large reservoirs puts pressure on underlying rocks
Subsidence of deep mine workings
Fracking
What is fracking?
Hydraulic fracturing of rock in order to release gas
What has Oklahoma experienced since fracking began?
An increase in minor earthquakes
When did fracking begin in Oklahoma?
2009
What are the 3 ways in which earthquakes can be measured?
Mercalli scale
Richter scale
Moment magnitude scale
What is MMS?
Moment magnitude scale
What is the highest point on the Richter scale?
10
What type of scale is the Richter scale?
A logarithmic scale
How many times greater is the amplitude for each whole number on the Richter scale?
10 times
How much greater is the amount of energy released for each whole number on the Richter scale?
30 times
Why is MMS used?
Some geologists are unhappy with the fundamentals of the Richter scale.
What does MMS identify?
Energy release
What is the scale of MMS?
1-10
What does the Mercalli scale measure?
The intensity of an event and its impacts.
How many points is the Mercalli scale?
12
What is Level 1 on the Mercalli scale equivalent to?
2 on the Richter scale
What is Level 12 on the Mercalli scale equivalent to?
8.5 on the Richter scale
Give two primary impacts of earthquakes
Ground shaking
Ground rupture
What does the severity of ground shaking depend upon?
The magnitude of the earthquake
Depth and distance to epicentre and focus
Geological conditions
What made the effects of the Mexico City earthquake in 1985 worse?
The ancient lake sediments upon which the city was built.
What is ground rupture?
The visible breaking and displacement of the earth’s surface.
Where does ground rupture often occur?
Along the line of a fault.
What does ground rupture pose a serious risk to?
Large engineered structures such as dams, bridges or nuclear power stations.
What are 5 main secondary impacts of earthquakes?
Soil liquefaction Landslides/avalanches Tsunamis Fires Effects on people and the built environment
When does soil liquefaction occur?
When violently shaken, soils with a high water content lose their mechanical strength and start to behave like a fluid.
What are landslides and avalanches?
Slope failure as a result of ground shaking
What are fires a result of?
Broken gas pipes and collapsed electricity transmission systems.
What do effects on people and the built environment include?
Collapsing of buildings, destruction of infrastructure, damage to the local economy
How long can the wave length of a tsunami wave be when in the open ocean?
Sometimes over 100 km
What is the wave height of a tsunami wave in the open ocean?
Less than 1m
How fast can tsunami waves move?
Over 700km per hour
When do tsunamis increase rapidly in height?
When they reach shallow water bordering land.
What is the first tsunami warning?
A reduction in sea level
What is the term used for a reduction in sea level?
A drawdown
How tall can tsunamis be?
25m
Is a tsunami event just one wave or multiple?
Multiple waves
Is the first tsunami wave always the biggest?
No
What do the effects of a tsunami wave depend on? (5)
Wave height and the distance it has travelled
Length of the event
Warnings
Coastal geography (on the coastal area and offshore)
Land use and population density
How far inland can tsunamis effect?
At least 500-600m inland
Give an example of a volcano related tsunami
Krakatoa volcanic eruption in 1883
How many people drowned in the 1883 tsunami?
Over 35,500
How far did the waves of the 1883 tsunami travel?
Around the world
What was the height of the tallest wave in the 1883 tsunami event?
Over 40m
Where are 90% of tsunamis generated?
The Pacific Basin
Why are so many tsunamis generated at the Pacific Basin?
Due to the tectonic activity around the edges of the basin.
Where are most of the tsunamis in the Pacific Basin generated?
Along destructive plate boundaries
At which destructive plate boundary in the Pacific basin do tsunamis occur? What percentage of all events is this?
Western side of the Pacific bordering the eastern side of the Indian Ocean. 25%
When was the Boxing Day tsunami?
December 2004
Where was the Boxing Day tsunami?
Indian Ocean off Sumatra
What was the Boxing Day tsunami generated by?
A 9.0 magnitude earthquake 25km below the Indian Ocean floor off northwest Sumatra.
How many people died as a result of the Boxing Day tsunami?
An estimated 300,000
What was a positive of the Boxing Day tsunami?
A warning system was set up among countries that border the Indian Ocean.
What was the economic damage of the Boxing day tsunami?
Less than $5billion
Where was the March 2011 tsunami?
Tohoku region of Japan, off the Pacific coast
Where did the 2011 Japan earthquake occur?
70km offshore
What was the magnitude of the Japan earthquake?
9.0
Which was the most powerful earthquake ever in Japan?
The Sendai earthquake, March 2011
How high were the March 2011 tsunami waves?
Over 40m in height
How far inland did some of the March 2011 tsunami waves reach?
Over 10km
How many deaths resulted from the March 2011 tsunamis?
16,000
How many people were injured by the March 2011 tsunami?
Over 6000
How many people were missing as a result of the March 2011 tsunami?
2,500
How many people were displaced as a result of the Japan tsunami?
300,000
How many buildings were completely destroyed by the Japanese tsunami?
127,000
Which nuclear power plant was seriously effected by the tsunami in Japan?
Fukushima
What was the evacuation area for the Fukushima nuclear power plant?
20km
What was the economic cost to Japan after the event?
$235billion
What was the insurance cost to Japan?
$30 billion
Which other country saw higher waves as a result of the March 2011 tsunami?
Chile saw waves 2m high
What are the 4 types of shock wave?
Primary/pressure waves- P waves
Secondary/shear wavers- S waves
Surface love waves- L waves
Rayleigh waves- R waves
In which order do the shockwaves arrive?
1st- P
2nd - S
3rd- L and R
What are P waves?
Compressional or longitudinal waves that push and pull the ground in the direction that the wave is moving.
How much damage do P waves cause?
Little damage
Which are faster: P or S waves
P waves
What are S waves?
Transverse waves where the vibrations are at right angles to the direction of travel.
What can S waves travel through?
Solids only
Which waves are more dangerous: P or S?
S
What are L and R waves a type of?
Surface wave
Which type of wave are responsible for most of the building damage?
Surface waves
How do Rayleigh waves move?
Elliptical motion- produces both a vertical and horizontal movement in the direction of movement.
What happens to the shape of the material after a surface wave has passed?
The material returns to its original shape.
How do L waves move?
Parallel to the Earth’s surface and perpendicular to the direction of propagation.
Are L waves horizontal or vertical?
Horizontal only
What is prediction?
The forecasting of the occurrence of an earthquake of a particular intensity in a specific location within a specific time limit.
What is long range prediction concerned with?
Forecasting the occurrence of an earthquake a number of years in advance.
When does medium term prediction occur?
A few months to a year before the event.
When does short term prediction occur?
A few hours or days before.
What are 9 earthquake warning signs?
Unusual animal behaviour Hydrochemical precursors Temperature change Water level Radon gas Oil wells Foreshocks Seismic gap Changes in seismic wave velocity
Give an example of unusual animal behaviour before an earthquake.
Snakes came out of hibernation a month before and earthquake in Haicheng, China in 1975. This was unusual because of low temperatures which would kill the snakes.
In Tadzhik and Uzbekistan what hydrochemical precursors have been observed?
An increase in the concentration of dissolved minerals in groundwater was noticed 2-8 days before an earthquake.
Give an example of a temperature rise before an earthquake.
A rise of temperature by 10 C was reported before earthquakes in Lunglin, China (1976)
Give two examples of observed water level change before an earthquake.
A rise by 3cm in Lunglin
A fall before the Nankai earthquake in Japan 1946
How can radon gas indicate an earthquake?
It is discharged from rock masses prior to an earthquake.
Give an example of where a increase in radon gas before an earthquake has been observed?
Tashkent 1972- increases in concentration ranging from 15-200% about 3 to 13 days before an earthquake.
How can oil wells indicate an earthquake?
Large scale fluctuations of oil flow from oil wells prior to earthquakes have been noticed in Israel (1969) and other countries.
Give an example of an earthquake that was successfully predicted based on foreshock observations.
The Oaxaca earthquake in Mexico, November 1978
What should be used when using foreshocks to predict earthquakes?
It should be supplemented by other methods of prediction as this method is not flawless.
What is seismic gap theory?
Regions where earthquake activity is less compared to its neighbourhood along plate boundaries are more likely to experience some earthquake activity.
Where has seismic gap theory successfully predicted an earthquake?
Along the San Andreas Fault 1989 6.9MMS
How can changes in seismic wave velocity be used to predict earthquakes?
The time lag between the arrival of P and S waves is called the lead time. This decreases significantly before an earthquake but returns back to normal just before an earthquake occurs. A longer period of abnormality indicated a larger quake.
What can also be measured and monitored to try and predict earthquakes?
Magnetic fields and known fault lines
What is a potential idea to try and prevent earthquakes?
Lubricate with water
What are the aims of FEMA?
Promote understanding of earthquakes and their effects
Better identify earthquake risk
Improve earthquake-resistant design and construction techniques
Encourage the use of earthquake-safe policies and planning practices.
What is protection?
Preparing for the event by modifying the human and built environment to decrease vulnerability.
What are the 3 main ways in which a building can be hazard-resistant?
Rubber shock absorbers in the foundations
Large concrete weight on top of the building
Cross bracing
How do rubber shock absorbers make a building more earthquake proof?
They allow some movement of the building
How does the large concrete weight at the top of a building help minimise the impact of an earthquake?
A computer programme causes it to move in the opposite direction to the force of the earthquake to counteract stress.
How does cross bracing help minimise the effect of an earthquake?
It holds the building together better when it shakes
What can be done to older structures to make them more earthquake proof?
They can be retrofitted
When was the Loma Prieta earthquake?
1989
What was the magnitude of the Loma Prieta earthquake?
6.9MMS
How many people died as a result of the Loma Prieta earthquake in California?
63
When was the earthquake in Armenia?
1988
What was the magnitude of the Armenian earthquake?
6.8MMS
How many people died as a result of the Armenian earthquake?
Over 25,000
Why was there such a big difference in the death toll between the Armenian earthquake and the Californian one?
In California there were more earthquake-proof buildings.
What is the main way in which loss of life can be minimised for many areas?
Through education
How can individuals prepare for earthquakes?
By securing homes, appliances and heavy furniture
Assembling “earthquake kits”
Where can earthquake drills take place?
Schools, offices and factories
Which country has a Disaster Prevention Day?
Japan
What did the American Red Cross do following the Loma Prieta event in 1989?
Issue a list of supplies that people should have in case of an earthquake.
What have been developed to cut off gas supplies if an earthquake of a certain magnitude occurs?
“Smart meters”
How is fire prevented after an earthquake in Tokyo?
The gas company has a network that transmits seismic information to a computer which then informs employees where to switch off major pipelines.
What does much of the preparation in California involve?
The establishment of computer programmes that will identify where emergency services should be sent to first.
How can land-use planning decrease vulnerability?
The most hazardous areas can be identified and then managed. Buildings such as hospitals and schools should be put in areas of low risk and areas of open space are needed.
What percentage of people affected by the Kobe earthquake in 1995 had earthquake insurance?
7%
When do most poor countries receive aid?
In the few days after the event.
How can people be warned about tsunamis?
Through tsunami warning systems
Where is the Pacific Warning System based?
In Hawaii
What have some countries built to try and reduce the risk of tsunamis?
12m walls
Why are the 12m walls likely to be ineffective?
Tsunami waves will be higher
