Tectonic Processes and Hazards

Question 1

What are Intra-Plate Earthquakes?

Answer 1

These occur in the middle or interior of tectonic plates and are much rarer than boundary earthquake. Scientists think that they occur when stress builds up in ancient faults -> causing them to become active again.
They are harder to predict as they don’t occur in well-defined patters.

Question 2

What are Volcanic Hazards?

Answer 2

Associated with eruption events.

Question 3

What is a Volcano?

Answer 3

A landform that develop around a weakness in the Earth’s crust from which molten magma, volcanic rock and gases are ejected and extruded.

Question 4

What are Seismic Hazards?

Answer 4

Generated when rocks within 700km of the Earth’s crust surface come under such stress that they break and become displaced.

Question 5

What are Tectonic Hazards?

Answer 5

These include earthquakes and volcanic eruptions as well as secondary hazards such as tsunamis and represent a significant risk in some parts of the world in terms of loss of life, livelihoods and economic impact.

Question 6

What Percentage of earthquakes are found along Plate Boundaries?

Answer 6

95%

Question 7

What Percentage of earthquakes are found in the Pacific Ring of Fire?

Answer 7

70%

Question 8

What is the Oceanic Fracture Zone (OFZ)?

Answer 8

Activity found in mid-ocean ranges e.g. the mid-atlantic ridge.

Question 9

What is the Continental Fracture Zone (CFZ)?

Answer 9

Activity found in mountain ranges e.g. across the himalayas.

Question 10

What are earthquakes Scattered in Continental Interiors?

Answer 10

Found along fault lines e.g. the Church Stretton Fault in Shropshire.

Question 11

How many Active Volcanoes are there Globally?

Answer 11

Around 500

Question 12

How many Volcanoes Erupt each year?

Answer 12

50

Question 13

Where can Volcanoes form?

Answer 13

-Majority on plate boundaries -> the type of plate boundary can determine whether a volcano exists and what type it is.
-Some on Hotspots.

Question 14

What is a Volcanic Hotspot?

Answer 14

An area in the mantle from which heat rises as a hot plume from deep within the earth, often called a ‘mantle-plume’.
High heat and low pressure at the base of the lithosphere enable melting of the rock.

Question 15

What is Sea Floor Spreading?

Answer 15

-This is the process of new crust pushing tectonic plates apart.
-In the middle of many oceans there are mid-ocean ranges or under water ranges, formed when magma is forced up from the asthenosphere and hardens forming new ocean crust.

Question 16

What is Subduction?

Answer 16

The process of a plate being destroyed as two oceanic plates or an oceanic and continental plate move towards each other, one slides under the other into the mantle, where it melts into an area called the Subduction Zone.

Question 17

What is Slab Pull?

Answer 17

Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it cools -> this causes it to sink into mantle under its own weight - pulling the rest of the plate down with it.

Question 18

What is Mantle Convection?

Answer 18

Heat produced by the decay of radioactive elements in the earth’s core heats the lower mantle -> Creating convection currents.
-These hot, liquid magma currents ae thought to move in circles in the asthenosphere - thus causing the plates to move.

Question 19

What is Palaeomagnetism?

Answer 19

-In the 1950s, studies of palaeomagnetism confirmed that sea floor was spreading. Every 400,000 years or so, the earth’s magnetic fields change direction i.e. the magnetic north and south pole.
-When lava cools and becomes rock, minerals inside the rock line up with the earth’s magnetic direction (polarity) at the time.

Question 20

What is the Earth’s Crust?

Answer 20

-It is made of Oxygen, Silicon, Aluminium, Iron, Calcium, Sodium, Potassium and Magnesium.
-Beneath continents the earth’s crust can be 30-70 km and under oceans it is 5-7 km.
-The crust is solid and is 1000°c at the base.

Question 21

What is the Lithosphere?

Answer 21

-It is made of rocks and minerals.
-The lithosphere includes the crust and the upper mantle so it’s about 100-300 km.
-The lithosphere is solid and is 300-500°c including the crust and upper mantle.

Question 22

What is the Asthenosphere?

Answer 22

-It is the section of the mantle directly underneath the lithosphere.
-It is made of periodtite which is a rock containing mostly minerals olivine and pyroxene.
-It is about 200 km thick.
-It is solid that can behave like liquid and is 1,500°c.

Question 23

What is the Mantle?

Answer 23

-It is made of mostly Iron, Magnesium, and Silicon.
-It is 3000 km thick, making it the thickest layer.
-It is a dense, semi-solid layer with temperatures of 1,000°c to 3,700°c.

Question 24

What is the Outer Core?

Answer 24

-It is made of Iron and Nickle.
-It is about 2,200 km thick.
-It is liquid and ranges from 4,500-5,000°c
-It is mainly heated by radioactive decay of the element Uranium and Thorium which churns turbulent currents. This generates electrical currents which generate earth’s magnetic field.

Question 25

What is the Inner Core?

Answer 25

-It is mostly made of Iron and Nickle making it extremely dense.
-It is about 1,200 km thick.
-It is solid and is about 5,200°c.
-The pressure is also well over 5 million times greater than the earth’s surface.

Question 26

What is a Plate Boundary?

Answer 26

When two tectonic plates meet, plate boundaries are formed.

Question 27

What are Plate Margins?

Answer 27

The areas adjacent (next to) the plate boundaries are plate margins.

Question 28

What is an example of a Divergent Plate Boundary with continental crust?

Answer 28

The east-African rift valley.

Question 29

What are Mid-Ocean Ridges?

Answer 29

A mid-ocean ridge is a seafloor mountain system formed by plate tectonics.
-New islands are formed
-Two oceanic crusts
-Submarine volcanoes
-Can extend for over 60,000 km

Question 30

What are Rift Valleys?

Answer 30

-Two continental crusts
-Land collapses
-The crust stretches
-Faults form

Question 31

What is the Subduction Zone?

Answer 31

Broad areas where two plates are moving together. Often the thinner, more dense oceanic plate descends beneath the continental plate.

Question 32

What is a Locked Fault?

Answer 32

In a subduction zone, as plates move tigether they can get stuck due to frictional resistance. Such faults may store strain for extended periods, that is eventually released in a large magnitude earthquake.

Question 33

What is the Benioff Zone?

Answer 33

An area of seismicity corresponding with the slab being thrust downwards in a subduction zone.

Question 34

Describe the San Andreas Fault.

Answer 34

-It is located in California.
-The fault is 1,300 km long and is 25km deep.
-It makes the junction between the North American and Pacific Plates.
-It has a north west - south east trend in movement.
-Both plates are moving north west, the pacific plate is being moved north west due to the sea floor spreading -> the pacific plate is moving faster than the North American Plate, so the relative movement of the North Americna plate is to the south east.

Question 35

Why is the San Andreas Fault a particular threat to the area?

Answer 35

-It has caused many large scale earthquake before and California is a very built up place with a large population meaning if there was an earthquake it would cause damage to a lot of infrastructure and so would costs a lot to repair or rebuild and so could cause a loss of jobs which would be bad for the local economy.
-It could also put lots of lives at risk and may cause people to have to re-house.
-It could also cause lots of disruption to wildlife and famous places like Santa Monica and San Diego.

Question 36

How is the San Andreas Fault monitored and when do scientists predict the next big earthquake will occur?

Answer 36

In 2004 the National Science Foundation and the USGS started to drill a deep hole to install instruments within the fault zone. The instruments are 2-8 km below the earth’s surface.
->This will provide information on the composition and mechanical properties of rocks in the fault one, the nature of the stress responsible for the earthwuakes, the role of fluids in controlling faulting and earthquake recurrence and the physics of earthquake initiation and rupture.

Question 37

What does Sinistral mean?

Answer 37

Movement to the left.

Question 38

What does Dextral mean?

Answer 38

Movement to the right.

Question 39

What is the Focus or Hypocentre of an Earthquake?

Answer 39

The point inside the crust from which the pressure is released.

Question 40

What is the Epicentre of an Earthquake?

Answer 40

The point on the surface directly above Focus or Hypocentre.

Question 41

What are Primary Waves?

Answer 41

-P waves are body waves (they travel through the Earth’s body).
-They are the fastest and the first to reach the surface (8km/sec).
-They travel through both solids and liquids.
-They move in a backwards and forwards motion.
-They are only damaging in the most powerful earthquakes.