Earthquakes

Question 1

Describe the global distribution of EQs in terms of plate tectonics.

Answer 1

• most occur in clearly defined linear patterns that generally follow plate margins- eg along the centre of the Atlantic ocean in association with the MAR (constructive pb)
• distinct lines of EQ around pacific ocean (destructive subduction zones)
• broad belts of EQ associated with subduction zones and collision boundaries (Himalayas)
• narrower belts associated with constructive plate margins, where new material is formed and plates diverge and conservative plate boundaries- eg. san andreas fault

Question 2

Describe the global distribution of Volcanoes in terms of tectonics.

Answer 2

• 3/4 of earths historically active volcanoes occur of the pacific ring of fire -eg. mt st. helens- relating to subduction beneath either oceanic or continental crust
• most formed at plate boundaries although some exceptions
• subduction in the ocean provides island arcs- eg. Alutian islands formed by subduction of Pacific Plate under the North American plate

Question 3

Describe the global distribution of earthquakes and volcanoes not in terms of plate tectonics. (intraplate earthquakes)

Answer 3

•HOTSPOTS- isolated plumes of rising magma responsible for both eq and volcanoes. eg. hawaiian islands are volcanic islands that stretch along the n/w pacific
•HUMAN CAUSES:
-Reservoirs: in deep, large reservoirs, the column of water in a reservoir may alter the in situ stress state of an existing fault or fracture
-Mining: mining leaves voids that generally alter the balance of forces in the rock. These collapse and produce seismic waves & in some cases, reactivate existing faults causing minor earthquakes
-shale gas extraction
-nuclear testing

Question 4

Describe the processes of a divergent/constructive pb and the earthquakes that occur there.

Answer 4

• plates diverge away from each other

* pressure realised readily near surface therefore shallow earthquakes with high frequency and low magnitude

Question 5

Describe processes at convergent destructive and collision boundaries and the eq that occur.

Answer 5

Destructive:
•oceanic plate subducts under continental plate
•deep earthquakes with high magnitude and low frequency
•deep ocean trench is formed

Collision:
•continental plate collided with continental
•fold mountains

Question 6

Describe the processes that occur at conservative boundaries and the eq that occur.

Answer 6

• continental plates slide past each other
• shallow earthquakes, some with high magnitude, low frequency activity when pressure does build up but lots with high frequency and low mag.

Question 7

Describe an earthquake.

Include P&S waves.

Answer 7

• a series of seismic waves that originate from the focus
•can be proceeded by smaller tremors (fore shocks) and after shocks
•seismic waves following an eq- p&s waves
P- comes first, fast, not much damage, can provide warning
S- do damage slower

Question 8

Describe the resultant hazards of eq. (hint: 4)

Answer 8

1.Liquefaction- •occurs due to the nature of rock beneath the round
•unconsolidated sediments shake in less predictable ways
•p waves turn solid sediments into fluids like quicksand by disrupting sub surface water conditions

2. Shaking- •caused by p&s waves reaching surface
   •responsible for most damage to structures, presents greatest hazard
3. Landslides- •debris flows can move rapidly, striking with little or no warning at avalanche speeds
   •travel several miles from their source, growing in size as they pick up trees, boulders and other materials
4. tsunamis

Question 9

what are the factors affecting eq damage?

hint: 8

Answer 9

1.strength and depth of quake- stronger the eq, greater the damage. shallower eq= greater damage as less energy is absorbed when it hits surface

2. population density
3. time of day
4. type of building
5. economic development
6. secondary hazards
7. type of rock and sediment
8. distance from epicentre