hazardous earth 3

Question 1

earthquake characteristics

Answer 1

• earthquakes occur when the build up of tectonic strain becomes too much and the lithospheric crust faults, releasing energy, which creates seismic waves.
  -the focus of the earthquake is the point of failure of the rocks, where stress is suddenly released. The epicentre is immediately above the point of failure on the earth’s surface.
• 75% of earthquakes orginate at shallow depths (0-70km). SHallow EQss can be deadly as they can release a lot of energy which does not have time to dissipate before it reaches the Earth’s surface.

Earthquakes release waves of enerygy:
- P waves = compressional waves - Move through material by squeezing and stretching the material in the same direction as the wave is moving. P waves are the fastest
- S waves = shear waves - Move materials at right angles to the wave direction

Question 2

ways eq magnitue is measured

Answer 2

1 - richter scale: 1935, measures magnitude by looking at the amplitude (height) of the largest seismic waves. It is logarithmic so each increase represents a tenfold increase in amplitude of wave. Does not take into account the damage cause by an eq e.g. buildings collapse, level of preparedness.
2 - moment magnitude scale - measures magnitude based on calculating the seismic moment of the earthquake, looks at the physical movement caused by the EQ. More accurate than Rs for high magnitude EQs above 6, but not used for maller earthquakes.
3 - modified mercalli scale - measures intensity of EQ by looking at surface damage plus impacts felt and seen, scale of 1-12. Not a precise measurement, no decimals, but qualitative.

Question 3

faults

Answer 3

Most EQs occur at boundaries, as plate movement results in a buil-up of pressure and so fault lines form, these faults can be seen as fault scarps: a small offset on the ground surfae where one side of the fault has moved.
Normal faults: divergent boundaries, the result of tension, with rocks displaced downwards relative to the other. On moves down the other moves away.
Reverse faults: convergent boundaries, result of horizontal compression with one block forced upwards. They are squeezed together and one moves up.
Strike slip: conervative boundary: two fault blocks move past each other horiontally in a sideways or shear motion.

Question 4

effects earthuakes have on landforms

Answer 4

Rift valley: A rift valley is a steep-sided valley formed by the downward displacement of a block of the earth’s surface between nearly parallel faults or fault systems e.g. Great African rift valley. The sunken part of the valley is a graben, the higher rock on each side are the fault scarps.

Fold mountains: Mountain ranges created where two or more of Earth’s tectonic plates collide at a continental - continental convergent boundary. When the 2 plattes move towards each other, the layers of sedimentary rock are crumpled and folded. e.g. Himalayas, Gohrka eq occured here 2015, 7.8, uplifted kathmandu by 60cm, moved kathmandu 1.2m south

Question 5

hazards created by earthquakes

Answer 5

1 - building collapse: buildings may topple over or pancake as internal walls collapse. Ground shaking can create more sway frequency of buildings so they collapse, not felxible enough to bend.
2 - liqeufaction - occurs in loose sediment. During ground shaking, the solid soil behaves like a liquid, water is displaced upwards making the ground soft so buildings and cars sink. e.g. Christchuch, NZ 2011.
3 - landslides/avalanches: earthquakes create stresses that make weak slopes fail e.g. Gorkha EQ killed 22 climber near base camp.
4 - tsunami - submarine EQ can cause seabed to rise so displace water, in deep water small waves form, as they approach coastline theshallow water causes wave height to increase. Just before it hits, there is a drawdown where the sea recedes rapidly.