hazards -DMFRP Flashcards
what is the spatial distribution of seismic hazards?
.they link to plate margins meaning the vast majority occur in linear belts along the boundary of tectonic plates
what percentage of earthquakes occur on plate boundaries?
90%
can earthquakes be intraplate?
.yes, some of these types of earthquakes can be caused by old fault line reactivation or human activity like mining
how is the magnitude of earthquakes measured?
.richter scale
.moment magnitude scale
.mercalli scale
what is the richter scale?
.a logarithmic scale that starts at 0 and each number is 10x the magnitude of the one before it
what is the moment magnitude scale?
.an adaptation of the richter scale
.uses complex maths to calculate the total amount of energy released in an earthquake
.ranges from 1-10
.more useful for large earthquakes
what is the mercalli scale?
.measures the intensity of an earthquake event and its impact rather than its magnitude
.12 point scale
what magnitude do destructive earthquakes tend to have?
6 and above
what is the frequency of earthquakes?
.earthquakes are frequent around the world and occur every day at boundaries
.larger earthquakes are less frequent
what is the regularity of earthquakes?
.earthquakes follow no pattern and are random so their is no regularity between events
can earthquakes be predicted?
.it is impossible to predict earthquakes, scientists can only predict areas that may be likely to receive earthquakes but not when or how powerful
what changes can occur before an earthquake that may hint at one occurring?
.raised ground water levels
.increased radon in ground water and argon in soil
.odd animal behaviour
what can be done whilst prediction isn’t possible?
.mapping possible hazards whereby appropriate action can be taken eg -implementing building codes
how are hazard maps made?
by considering:
-past faults and earthquakes
-behaviour of seismic waves as they travel through parts of the crust
-near surface site conditions
what can hazard maps be used for?
.land use planning
.mitigation
.emergency response
what is the seismic gap theory?
.the theory that over long periods of time, the displacement on any segment of an active fault line must be equal to that experienced by all the other parts of the fault
what does the seismic gap theory tell us about active fault lines and earthquakes?
.that an earthquake may be due to occur on an active fault line but that doesn’t mean it will happen
