Tectonic Hazards Flashcards
Fault line
Crack/boundary between two tectonic plates
Hypocentre
Focus
The point at which the seismic waves are released
Epicentre
Directly above the hypo-centre. The point on the earths surface which has the most shaking and energy
Seismic waves
Ripples of energy released from the hypocentre
What are p waves?
They are primary waves that are caused by compression - pushing and pulling in the direction of travel
They are the fastest and arrive first
What are S waves?
Slower and only move through sold rocks, up and down movement
60% of the speed of p waves
Only through crust
What are L waves?
Love waves
From epicentre, only travel through crust, fastest surface wave
Moves from side to side as it moves forward
Causes the most damage due to longer wavelength and focus of energy at the surface
Moment magnitude scale
Measures the magnitude so the power by measuring how much energy is being released
Scale is logarithmic - each level is x10 more powerful
What are factors that explain the intensity of an earthquake?
Magnitude
Distance from the hypocentre
Bedrock and soil - pwaves travel fast through hard rock
What is the modified mercalli scale?
Reflects the effect and intensity of earthquake
Subjective scale
What does shaking depend on?
magnitude of quake
distance from epicentre
depth of focus (focal length), e.g. Haiti and
Christchurch
rock type (amplification) e.g. Haiti and
Christchurch.
Secondary hazards
Tsunami
Mudslides
Sink whole
Landslides
Primary hazards
Caused by the initial processes - ground shaking and crustal fracture
Secondary hazard
Are the side effects or the knock on impacts of primary hazards
What is liquefaction?
Loosely packed grains of soil are held together by friction, pores spaces fill with water
Shaking destabilises the soil by increasing the space between grains, with its structure lost the soil flows like a liquid
The soil then moves downslope which makes the foundation unsupported which causes buildings to sink and collapse
How do slope process and earthquake relate?
Mass movements
Occur naturally at coasts
Earthquakes with magnitude over 4 can increase likelihood as the shaking puts more stress on to the slope causing it to fail
What is the distribution of tectonic hazards?
Wide spread but mostly surrounding the ring of fire
- some hazards aren’t located due to hotspots
Intra plate
Hazard that occurs in the middle of a plate
Plate tectonic theory
The theory that the earths surface is a huge jigsaw of irregular slabs which are moving constantly
Inner core
6000 degrees
Inner - solid iron
Most dense
Outer core
Liquid nickel and iron - swirling around making magnetic swirls
4500-6000 degrees
Semi molten
Mantle
Widest layer
Asthenosphere = solid below this is molten where plates float
Crust
Continental plates are older, thicker but less dense
Oceanic are thin but more dense - basalt
Outer shell is solid rock
Convergent plate boundary - oc
Oceanic meets continental Subduction Mantle, melts Deep ocean trenches Fold mountains Frictional drag - intermediate and deep earthquakes in Benioff zone -volcanic eruptions