Geography tectonic hazards

1.1-1.3

natural hazard

a naturally occurring process or event that has the potential to affect people

natural disaster

a major natural hazard that causes significant social, economic and environmental damage

vulnerability

the ability to anticipate, cope with, resist and recover from a natural hazard

Degg’s model

a model to show the point at which a natural hazard becomes a natural disaster

seismic waves

shock waves released by tectonic movements

tectonic plates

broken up parts of the lithosphere

lithosphere

the solid part of the upper mantle and crust

mantle convection

long thought to be the driver of tectonic plates, it involves magma close to the core heating up due to heat radiating from radioactive decay in the core. This magma then rises, and subsequently cools, sinking back down and creating a current

slab pull

newly formed crust at mid-ocean ridges becomes denser and thicker as it cools, causing it to sink into the mantle under its own plate, bringing the rest of the plate down with it

subduction

as one plate slides under the other, it melts in the mantle in an area known as the subduction zone. This means crust is constantly being created and destroyed

sea-floor spreading

when plate boundaries move apart magma rises through the cracks to form new crust, which pushes the plates apart

paleomagnetism

the study of past changes in the earth’s magnetic field

plate margins

areas adjacent to plate boundaries

benioff zone

planar zone of seismicity corresponding with the going down slab in the subduction zone

fold mountains

mountains caused by the continental plate bending upwards on a convergent plate boundary

island arcs

found at oceanic-oceanic convergent plate boundaries, they are underwater volcanoes that have turned into islands

collision margin

where two continental plates meet

transform fault

a major break between two crusts on a large scale

rift valleys

where two continental crusts are moving away from each other and the crust stretches, creating a series of parallel faults

focus/hypocentre

the point in the crust from which the seismic waves radiate from

epicentre

the point on the surface directly above the focus/hypocentre

primary waves

body waves that travel through solids and liquids and are the fastest and first to reach the surface. They are only destructive in the most powerful earthquakes

secondary waves

60% of the speed of p waves, and can only travel through solids. They travel in a sideways motion, shaking at right angles to the direction of travel. They do more damage than p waves

love waves

these are the slowest but the most destructive, shaking the ground from side to side. They are larger and focus all their energy on the earth’s surface

Moment Magnitude Scale (MMS)

uses the size of seismic waves, amount of slippage, area of fault surface broken by the earthquake and the resistance of the affected rock

Modified Mercalli Intensity Scale

uses qualitative data to place an earthquake froim a scale of I to XII

Earthquake primary effects

1. Ground shaking- causes infrastructure to collapse, killing or injuring those nearby

2. Crustal fracturing- energy released from the earthquake causes earth’s crust to crack

Earthquake secondary effects

1. liquefaction- violent shaking during an earthquake causes surface rock to lose its strength and behave more like a liquid than a solid. This causes roads and buildings to tilt or sink and can disrupt gas lines

2. landslides and avalanches- ground shaking places stress on slopes so that they fail. This accounts for a large proportion of damage and loss in an earthquake

3. tsunami- some underwater earthquakes generate tsunamis that cause major problems for coastal areas

aftershocks

small earthquakes that occur in the period of time after an earthquake, that are caused by the crust readjusting. Aftershocks can be damaging, some causing liquefaction

intra-plate earthquakes

occur when stress builds up in ancient faults, causing them to be active again