Tectonic Hazards- EQ1: Locations at Risk of Tectonic Hazards Flashcards
Natural Hazard
A naturally occurring process or event that has the potential to affect people and their livelihoods
Global Distribution of Earthquakes
Commonly found in clusters along plate boundaries (90%) or intra-plate
Global Distribution of Volcanoes
Commonly found at plate margins such as the Pacific Ring of Fire (60%) or hotspot regions
Global Distribution of Tsunamis
Generated along subduction zones and 90% around the Pacific Basin
Divergent (conservative) Plate Boundaries
Two plates are moving away from each other leading to new crust being created by magma being pushed up from the mantle
Convergent (destructive) Plate Boundaries
Denser oceanic plate subducts under the lighter continental plate. Built up pressure from the plate melting due to friction can cause a volcano. The movement of plates can cause earthquakes
Transform Plate Boundaries
Two plates are sliding past each other, often at different speeds which causes a build up of friction as they drag against eachother
Volcanic Hotspot
A volcanic hotspot is an area in the mantle from which heat rises as a hot thermal plume from deep in the Earth
How do volcanoes form at hotspots?
Heat melts through the lithosphere, rising through the cracks to form active volcanoes on the Earth’s surface. As the tectonic plate moves over the hotspot like a conveyer belt, a series chain of volcanoes forms called archipelagos (e.g. Hawaii)
Oceanic Crust
Thinner, denser, mainly made of basalt
Continental Crust
Thicker, less dense, mainly made of granite
What drives plate movement?
Convection currents
How does slab pull drive plate movement?
The force of an oceanic plate plunging into the mantle due to it’s own weight drives the movement of the plate
How does ridge push drive plate movement?
Rigid lithosphere slides down the hot, raised asthenosphere below mid ocean ridges, pushing plates away from each other
Sea Floor Spreading
Continuous input of magma forming a mid ocean ridge such as the Mid Atlantic Ridge
Paleomagnetism
Record of the Earth’s magnetic field in rocks, sediment and archaeological materials
How does paleomagnetism help the study of plate tectonics?
Rocks that contain minerals align with the magnetic field preserving the direction of the magnetic field at the time of their formation which allows geologists to age the rock and map the position of the field for that date.
Locked Fault
A fault that is not slipping because the frictional resistance on the fault is greater than the shear stress across it.
Why are locked faults a cause for concern?
Locked faults can hold for hundreds of years that is eventually released in a high magnitude earthquake
Benioff Zone
Area of seismicity corresponding with the slab being thrust downwards in a subduction zone
3 Types of Seismic Waves
P Waves
S Waves
L Waves
P Waves
-Caused by compression
-Spread quickly from the fault
S Waves
-Vibrate at right angles to the direction of travel
-Can’t travel through liquids
-More destructive than P Waves
-Slower than P Waves
L Waves
-Surface waves
-Vibrations in the horizontal plane
-High amplitude
Hypocentre
Point within the Earth where the earthquake ruptures
Soil Liquefaction
Water-saturated material temporarily loses normal strength and behave like a liquid under the pressure of strong shaking
Epicentre
Point on Earth’s surface directly above the hypocentre
Landslides
Secondary earthquake hazard where slopes weaken and fall
How are tsunamis generated?
-Series of waves caused by sea bed displacement
-Often caused by submarine earthquakes at subduction zones
-Leads to the displacement of a water column
How is and earthquake generated?
-Gradual build up of tectonic strain
-When pressure exceeds strength of fault, the rock fractures
-Produces a sudden release of energy, creating seismic waves radiating from point of fracture
-Brittle crust then rebounds either side of fracture (ground shaking)
Secondary Hazards of Earthquakes(2)
-Liquefaction
-Landslides
Primary Hazards of Volcanic Eruptions (5)
-Pyroclastic flows
-Tephra
-Lava flows
-Volcanic gases
-Ash falls
Primary Hazards of Earthquakes(2)
-Crustal fracturing
-Ground shaking
Lahars
Volcanic mudflows generally composed of fine sand and silt material
Secondary Hazards of Volcanoes(2)
-Lahars
-Jokulhaup
Jokulhlaups
Glacial outburst flood which have a very quick onset and rapid discharge of large volumes of water, ice and debris from a glacial source that has been melted
Volcanic Eruptions at Convergent (conservative) Boundaries
Larger magnitude due to subduction of old oceanic lithosphere producing andesitic lava
Volcanic Eruptions at Divergent (destructive) Boundaries
Smaller magnitude due to rising magma being basic in nature
