Seismic hazards Flashcards
What is the focus ?
The point at which this pressure release occurs within the crust.
What is the epicentre ?
Point immediately above the focus on the earths surface.
What plate boundary have the most powerful earthquakes ?
Destructive
What are the three focus depths and which one causes the bigger damage?
Shallow focus, Intermediate, Deep - Shallow
What do constructive margins to do an earthquake ?
The boundary is marked by transform faults and differential movement produces earthquake.
How can humans cause minor earthquakes ?
building large reservoirs which puts pressure on underlying rocks, Deep mining.
What does the moment magnitude scale measure ?
Measures the size of an earthquake in terms of energy released.
What does the mercalli scale measure ?
Measures the intensity of the impact and its impact.
What are the primary effects of an earthquake and what are causes these effects?
Ground shaking - shock waves travelling through the crust from the focus up to the surface and radiating outwards
Ground rupture - the visible breaking and displacement of the earths surface.
What are the secondary effects of an earthquake ?
Soil liquefaction - when soils with high water content are violently shaken they lose their mechanical strength and behave like a fluid.
Land slides - Slope failure as a result of ground shaking
Tsunamis - Giant sea waves created by a shallow focus underwater involving movement of the sea bed or landslides into the sea.
Fires - Broken gas pipes and collapsed electricity systems.
What do the effects of a tsunami depend on ?
Height of wave and distance it has travelled, Length of the event, Coastal land use and population density
What is the nature of seismic hazards ?
As the crust of the earth is mobile there tends to be slow build-up of stress between masses of rocks moving in different directions, it then gets released and causes an intense shaking motion.
