Earthquake Hazards Flashcards
What are the three types of seismic wave?
Primary, Secondary, Love
What does the Mercalli Scale record?
The intensity and the effects of an earthquake
What scale does the Mercalli Scale use?
12 values in Roman numerals from I (hardly felt) to XII (total destruction)
What does the Moment Magnitude Scale record?
An earthquakes magnitude based on its seismic moment
What scale does the Moment Magnitude Scale use?
10 values (1 being lowest and 10 highest). An increase of one number means the quakes magnitude is 10x greater than the number prior
What are five factors affecting the Mercalli Scale?
Earthquake size, Depth of focus, Distance from epicentre, Ground conditions, Building quality
Define Isoseismal Lines
Lines connecting points on the earth’s surface at which earthquake intensity is the same/areas of equal intensity of damage
What are five effects of an earthquake?
Ground shaking, Liquefaction, Landslides, Seiche, Tsunami
Define Hazard
Something that can cause bodily harm
Define Risk
Chance of something happening and causing harm
What are seven factors affecting the risk of damage to property and loss of life?
Population density, Building design and density, Distance from epicentre, Level of development, Ground conditions, Coastal location, Magnitude
Define Earthquake Precursor
A wide variety of physical phenomena that reportedly precede at least some earthquakes
What are seven examples of earthquake precursors?
Groundwater level, Radon emissions, P-wave velocity, Electrical resistivity, Seismic gap theory, Earthquake lights, Animal behaviour
Define Seismic Gap
Where there has been less than expected movement (earthquakes) compared to other areas along the same fault
Define Geohazard
A geological condition that is dangerous (or potentially dangerous) to the environment and the people who live in it
What are three ways risk can be reduced?
Enforce up to date building codes, Improving emergency response and basic infrastructure, Preparing for emergencies which will arise after an earthquake
Define Return Period
The average length of time for an earthquake of a given magnitude to occur again or to be exceeded
Return Period =
Number of years on record + 1/Number of recorded earthquakes
Define Ground Acceleration
How hard the ground shakes during an earthquake. It is equal to the amplitude of the seismic wave and the movement can be in both horizontal and vertical planes
What are three management strategies for earthquakes?
Reducing the impact of ground acceleration, Site selection, Aseismic building design
Define Site Selection
How city planners decide on the correct site for buildings
What building materials are best for reducing earthquake damage?
Wood - wooden structures are flexible so accept a certain amount of strain
What two building profiles are less likely to experience damage from an earthquake?
Single storey, Stepped profile
What four building profiles are more likely to experience damage from an earthquake?
Multi-storey, Varied height, Angled wings, Soft storey
What are four examples of engineering components which reduce the resonance of a building during an earthquake?
Base isolators, Hydraulic dampeners, Pendulum or active mass balance, Cross bracing
What can be used to stop pipes leaking during an earthquake?
Smart or flexible shut off valves on services
What are two examples of building foundations to minimise damage during an earthquake?
Raft foundations, Piles
How do tsunamis change with respect to speed?
As the wave gets closer to land, it slows down. The wave behind it is still travelling fast so the amplitude is increased, and wavelength decreased
What are four examples of tsunami management strategies?
Tsunami wall, Forest or mangrove swamp, Building on stilts, Roads on raised embankments
What are four examples of things done by DART?
Detect earthquakes, Check location and magnitude, Assess likelihood of tsunami, Notify countries
