seismic hazards Flashcards
(27 cards)
what is liquefaction?
Liquefaction is where compact sediment loses strength and stiffness because of stress of shaking so the ordinary solid acts as a liquid.
-most common in loose sands
-liquefaction can cause buildings to collapse as well as risk to life as it acts like quick sand.
what is an aftershock?
-aftershocks are earthquakes that follow on from the main event and may last for months afterwards.
-they are caused by the earth settling back after the disruption of the first displacement.
what is an example of an aftershock?
- the 8.1 mag Indonesian earthquake was followed by many aftershocks, one being 6.1 magnitude
what are reasons for the difference in nature of seismic hazards?
-type of plate boundary- constructive high frequency low density, conservative/destructive- low frequency, high density
-nature and rate of plate movement
-depth of focus
what are some human factors affecting earthquake damage?
-population density
-preparedness
-education
-building design
-time of day
-number of secondary hazards
what are some physical factors that affect earthquake damage?
-earthquake depth
-earthquake strength/magnitude
-geology- clay prone to liquefaction
-distance from epicentre- the seismic energy reduces with distance as it is absorbed
what are the primary hazards of an earthquake?
-earthquakes
-shockwaves
-ground shaking
what are secondary hazards of an earthquake?
-landslides/avalanches
-fires
-tsunamis
-soil liquefaction
what are the three types of earthquakes?
-plate movement
-volcanic earthquakes
-human induced- fracking, water extraction
how many earthquakes occur each year?
-500,000 detectable earthquakes each year
-we feel about 10% of these
what is the focus?
-the focus is the point in the earths crust where the earthquake starts
what is the Epicentre?
-the epicentre is the point on the earths surface directly above the focus
what are the measurements for a shallow, intermediate and deep focus?
- a shallow focus is 0-70 km deep- accountable for 75% of all energy released
-an intermediate focus is 70-300km deep
-a deep focus is 300-700 km deep
How are earthquakes distributed?
-along plate margins
-pacific ring of fire
-form linear patterns
-along fault lines
-great African rift valley
What can you predict about earthquakes?
-measure tremors, time intervals and radon gas
- laser beam can be put either side of boundary to see when breaks
-where they occur on a mapped plate boundary
-where will have stronger or less severe based off type of plate boundary
What can you not predict about earthquakes?
-can’t tell exactly where energy will be released
-the date and time of the earthquake
-often no warnings or signs
Why measure earthquakes?
-allow for evacuation
-so seismologists can know more about how and why they happen
-to help evacuate the effectiveness of earthquake management
-to be able to make meaningful comparisons between earthquakes
Where are tsunamis most likely to occur?
Tsunamis are most likely to occur along destructive margins where two oceanic crusts are colliding
What are ways to measure magnitude?
-Richter scale
-modified Mercalli Intensity Scale
-Moment magnitude scale
What are the different types of seismic waves?
-primary waves
-secondary waves
-love waves
-Rayleigh waves
How does a primary wave move?
It is the first to travel and fastest but they are weak and cause surface to move back and forth as they push and pull on rocks
- dogs often hear this and bark
How do secondary waves move?
Secondary waves are slower than primary but more powerful and move rock back and forth as they move perpendicular to the direction of propagation
-can only move through solid rock
How do love waves move?
Love waves travel near the surface so are powerful and go up and down and side to side so make the rock move side to side
How do Rayleigh waves move?
Rayleigh waves radiate from the epicentre in complicated rolling motions and move the ground up and down
