Tectonics EQ1

Question 1

What is the structure of the Earth

Give the basic characteristics of each layer

Answer 1

INNER CORE - solid, 6000 degrees
OUTER CORE - semi molten, 4500 degrees
MANTLE - Thickest layer, solid, tectonics float on the upper part.
CRUST - oceanic (thin but dense), continental (thick but less dense)

Question 2

Where are most volcanoes/earthquakes found?

Answer 2

“ring of fire” - 75% of EQs.
pacific ocean

Question 2

What are Intra Plate Earthquakes?

Answer 2

EQs in the middle of a plate -
old fractures/ancient fault lines
mantle hotspots
stress concentrations

EG Mississipi river area

Buildings/ enviroment not often protected as very rare and unpredictable

Question 3

What plates are volcanoes found?

Answer 3

Divergent oceanic ridges (EG mid atlantic ridge) - rift zones
Over hot spots (Hawaii)
Subduction zones (a convergent oceanic and continetnail)

Question 4

What is a mantle plume?

Answer 4

a hot, buoyant mass of material that rises from deep within the Earth’s mantle

can cause volcanoes.

Question 5

Evidence of continential drift?

Answer 5

Jigsaw fit = the similartiy of the outlines of coastrss of Eastern SA and West Africa.
**Geological fit **= The geology / sequences Scotland - Canada
Fossil evidence = Many examples of fossils found on seperate continents and nowhere else - Freshwater reptile “mesosaruas” in Africa and SA.

Question 5

What is the theory of tectonics?

Answer 5

Builds on the concept of continential drift -
“The large scale movement of the Earth’s tectonic plates.”

Question 6

What are the 3 ways tectonics move

Answer 6

Mantel Convection - Heat produced by the radioactive decay in Earth’s core heats the lower mantle, creating convection currents. This moves in circles throughout Earths Mantle pushing plates around.

**Slab Pull - As a denser, older oceanic plate subducts, gravity pulls it deeper into the mantle, dragging the rest of the plate with it.
**
Ridge Push - At mid-ocean ridges, newly formed crust is higher in elevation and slides away due to gravity, pushing the plate apart.

Question 7

What is a sea floor spreading?

Answer 7

Seafloor spreading is when new oceanic crust forms at mid-ocean ridges as magma rises and solidifies, pushing plates apart. two plates slide away from eachother. new plate forms inbetween and pushes them further.

EVIDENCE = paleomagnetism = as the new rock forms the magnets align with NORTH/SOUTH and then stay that way once they have cooled. The poles switch every 300,000 years so you can see magnets facing the wrong way.

Question 8

What are the causes of Earthquakes (4) ?

Answer 8

1. Movement of plates are preceded by the gradual build up of tectonic strain which stores elastic energy in the crustal rocks.
2. When pressure exceeds strenght of fault, the rock fractures - THE FOCUS.
3. this produces a sudden release of energy which creates seismic waves that radiate from the point of the fracture.
4. The brittle crust then rebounds either side of the fracture, the earthquake is now felt on the surface.

Question 9

How do EQ waves help us understand the structure of the Earth?

Answer 9

P waves can travel through core but are refracted as they go through.

S waves cant travel through liquid - so doesnt go through core.

Question 9

Types of seismic waves and a brief description of each?

Answer 9

P-Waves (Primary) – Fastest, travel through solids & liquids, compressional (push-pull motion).

S-Waves (Secondary) – Slower, travel only through solids, shear motion (side-to-side).

Love Waves – Slowest, travel along the Earth’s surface, cause most damage (rolling & shaking motion).

Question 10

What are the secondary hazards of EQs?

Answer 10

Soil Liquefaction: Material saturated in water loses its strength and behave like a liquid. Causes buildings to sink or tilt.

Landslides: 70% of all EQs death are from landslides

Question 11

What are the 3 principles that cause volcanic eruptions?

Answer 11

1. At subduction zones, an oceanic plate (denser) sinks beneath a continental or another oceanic plate. As it descends, the plate melts due to heat and pressure, forming magma. This magma rises to the surface, creating volcanoes. - COMPOSITE VOLACNO, THICK VISCOUS VIOLENT LAVA.
2. Hotspot volcanoes. - shield
3. Divergent plate boundaries - magma rises between seperating plates. SHIELD VOLACNO - frequent but gentle eruptions, thin runny lava

Question 11

What are the causes of Tsunamis?

Answer 11

EG.

Plates push towards eachother eventually slip which releases all the stored elastic energy.

Energy is released into the water - water above EQ suddenly shifts up displacing the water column.

Question 12

What is a Tsunami?

Answer 12

Caused by EQs, or volcanoes.
A major displacement of a water column.
Travel over 800KM/H
Amplitude increases as it reaches shore as friction slows the base down and letting it build height.

Question 12

Why are some volcanoes more hazardous than others?

Answer 12

1. Viscosity of magma - more viscous = more explosive.
2. popultion proxmity
3. materials ejected. - pyroclastic flows etc

Question 13

Best case study of a Tsunami?

Answer 13

2011 Tohoku -
9.0 magnitude EQ formed Tsunami
killed 20,000 people
Fukushima.

Question 14

What can earthquakes also cause?

Answer 14

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```Lava Flows – Molten rock erupts and moves downhill, destroying everything in its path but usually slow-moving.

Pyroclastic Flows – Fast-moving, extremely hot clouds of ash, gas, and volcanic debris that incinerate anything in their way.

Ash Falls– Volcanic ash ejected into the air, settling over wide areas, disrupting transport, air quality, and infrastructure.

Gas Eruptions – Toxic volcanic gases (e.g., CO₂, SO₂) released, which can suffocate people and animals or cause acid rain.

Lahars – Volcanic mudflows formed when ash mixes with water, flowing rapidly and burying landscapes.

Jökulhlaups – Sudden, catastrophic glacial floods caused by volcanic heat melting ice, leading to destructive surges of water.