Tectonic Hazards Flashcards
What are the different levels of the internal structure of the Earth?
Inner core
Outer core
Lower mantle
Upper mantle
Crust (Oceanic, Continental)
What are the different types of Plate Boundaries?
Convergent (destructive)
Conservative
Divergent (constructive)
Oceanic-oceanic
Continental-continental
What happens at Convergent plate boundaries?
two tectonic plates move towards each other, causing one plate to be forced beneath the other, typically resulting in the formation of deep ocean trenches, volcanic activity, and earthquakes, depending on whether the colliding plates are oceanic-oceanic, oceanic-continental, or continental-continental; this process is often referred to as “subduction” when one plate dives under the other.
What happens at Conservative plate boundaries?
two tectonic plates slide past each other horizontally, causing no new crust to be created or destroyed, but resulting in significant shallow-focus earthquakes due to friction and pressure build-up as the plates snag on each other while moving at different speeds or in opposite directions; this type of boundary is characterized by the absence of volcanic activity.
What happens at Divergent plate boundaries?
two tectonic plates move apart from each other, causing magma from the Earth’s mantle to rise to the surface, solidify, and create new oceanic crust, resulting in features like mid-ocean ridges, rift valleys, and volcanic activity; essentially, this is where new crust is generated on the Earth’s surface.
What happens at Oceanic-oceanic plate boundaries?
the denser, older oceanic plate subducts beneath the younger, less dense plate, leading to the formation of deep ocean trenches and volcanic island arcs due to the rising magma from the melting subducted plate; this process is accompanied by frequent earthquakes and volcanic activity.
What happens at Continental-continental plate boundaries?
when two continental plates collide, the land is forced upwards due to neither plate being dense enough to subduct, resulting in the formation of fold mountains like the Himalayas, accompanied by significant earthquake activity but with no volcanic activity present; this is also known as a collision boundary.
What are Intra-plate earthquakes?
INTRA-PLATE EARTHQUAKES
- It has been suggested that they occur when stress in an ancient fault causes them to become active again
- occur in the middle of plates.
Example = A magnitude 5.2 earthquake struck near Grimsby in 2008: there were no deaths, but a 19 year old suffered a broken pelvis when a piece of chimney fell through the roof and onto his bed; the total cost of insurance pay-outs was £30m.
What are Hotspot volcanoes?
HOTSPOT VOLCANOES
Mantle plumes (in a fixed position), comprised of rising magma, erupt onto the sea floor as the tectonic plate moves, the volcano is carried away with it, and a new volcano forms eventually this process creates a chain of volcanic islands, an archipelago.
Example = Hawaii’s 8 islands.
What is Mantle Convection?
Heat produced by radioactive decay in the core heats the lower mantle, producing convection currents which pull the plates in different directions.
What is Paleomagnetism?
Every 400,000 years, the Earth’s magnetic fields change direction, so alternating lines of minerals inside cooled lava facing different polarities can be found.
What is Seafloor spreading?
Magma forced out of the asthenosphere forms new oceanic crust, pushing existing oceanic plates apart.
What is Slab pull?
Newly formed oceanic crust becomes denser and thicker as it cools, causing it to sink underneath it’s own weight - pulling down the rest of the plate with it.
What is Subduction?
At a subduction zone, on a convergent margin, denser crust is pulled underneath less dense crust.
What is the fault of an earthquake?
A fracture in the rocks that make up the earth’s crust.
What is the epicentre of an earthquake?
The point at the surface of the earth directly above the focus.
What is the focus (hypo centre) of an earthquake?
The point within the earth where an earthquake rupture starts.
What are the plates?
Massive rocks that make up the outer layer of the earth’s surface, and whose movement along faults triggers earthquakes.
What are seismic waves?
Waves that transmit the energy released by an earthquake.
What is an earthquake?
An earthquake is the shaking of the ground caused by sudden motions along faults, or fractures in the earth’s crust.
What are P waves?
A type of Seismic Wave: Primary
- Fastest and first to reach the surface
- Travel through both solids and liquids
- Shake in a backwards and forwards motion
- Only damaging in the most powerful earthquakes
What are S waves?
A type of Seismic Wave: Secondary
- 60% of the speed of P waves
- Only travel through solids
- Move in a sideways motion, shaking perpendicular to the direction of travel
- More damaging than P waves
What are L waves?
A type of Seismic Wave: Love
- The last waves to arrive
- Shake the ground from side to side
- Larger movement
- Focus all of their energy on the Earth’s surface
- Do the most damage
What is Crustal fracturing?
Energy released causes the crust to crack - leaving large gaps in the earth
Example = Myanmar
What is ground shaking?
Causes buildings roads and infrastructure to collapse - killing or injuring those nearby
Example = Haiti 2010, many poorly built buildings, especially slum housing, and around 230,000 died
What are landslides?
The ground shaking places stress on slopes so they fall, resulting in land/rock/mudslides or avalanches. Many of these effects account for a large proportion of the damage and injuries caused by an earthquake including a quarter of deaths in China 2008 earthquake were caused by landslides
What is liquefaction?
Violent shaking causes surface rocks to lose their strength and liquefy; the subsoil can no longer support the foundations of buildings or other structures, so buildings/roads may tilt/sink
Example = Loma Prieta California 1989, the freeway collapsed because it was built on soft mud, killing > 40; this can hinder rescue efforts and disrupt underground power/gas lines
What is focal depth?
It affects the strength of an earthquake:
- shallow focus = high speed, causes greater damage at the surface
- Deep focus = happen in Benioff zones, have a larger magnitude, and release more energy
What are Benioff zones?
the Benioff zone is an area of the Earth’s crust where earthquakes occur at a destructive plate boundary.
What are Micro strategies in modifying the event?
Micro = strengthening individual buildings and structures against hazardous stress
What are Macro strategies in modifying the event?
Macro = large-scale protective measures designed to protect whole communities
What are mitigation strategies?
Mitigation is about the modification of the loss burden – insurance is a simple way of achieving this
