Tectonic Processes and Hazards Flashcards
What are Intra-Plate Earthquakes?
These occur in the middle or interior of tectonic plates and are much rarer than boundary earthquake. Scientists think that they occur when stress builds up in ancient faults -> causing them to become active again.
They are harder to predict as they don’t occur in well-defined patters.
What are Volcanic Hazards?
Associated with eruption events.
What is a Volcano?
A landform that develop around a weakness in the Earth’s crust from which molten magma, volcanic rock and gases are ejected and extruded.
What are Seismic Hazards?
Generated when rocks within 700km of the Earth’s crust surface come under such stress that they break and become displaced.
What are Tectonic Hazards?
These include earthquakes and volcanic eruptions as well as secondary hazards such as tsunamis and represent a significant risk in some parts of the world in terms of loss of life, livelihoods and economic impact.
What Percentage of earthquakes are found along Plate Boundaries?
95%
What Percentage of earthquakes are found in the Pacific Ring of Fire?
70%
What is the Oceanic Fracture Zone (OFZ)?
Activity found in mid-ocean ranges e.g. the mid-atlantic ridge.
What is the Continental Fracture Zone (CFZ)?
Activity found in mountain ranges e.g. across the himalayas.
What are earthquakes Scattered in Continental Interiors?
Found along fault lines e.g. the Church Stretton Fault in Shropshire.
How many Active Volcanoes are there Globally?
Around 500
How many Volcanoes Erupt each year?
50
Where can Volcanoes form?
-Majority on plate boundaries -> the type of plate boundary can determine whether a volcano exists and what type it is.
-Some on Hotspots.
What is a Volcanic Hotspot?
An area in the mantle from which heat rises as a hot plume from deep within the earth, often called a ‘mantle-plume’.
High heat and low pressure at the base of the lithosphere enable melting of the rock.
What is Sea Floor Spreading?
-This is the process of new crust pushing tectonic plates apart.
-In the middle of many oceans there are mid-ocean ranges or under water ranges, formed when magma is forced up from the asthenosphere and hardens forming new ocean crust.
What is Subduction?
The process of a plate being destroyed as two oceanic plates or an oceanic and continental plate move towards each other, one slides under the other into the mantle, where it melts into an area called the Subduction Zone.
What is Slab Pull?
Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it cools -> this causes it to sink into mantle under its own weight - pulling the rest of the plate down with it.
What is Mantle Convection?
Heat produced by the decay of radioactive elements in the earth’s core heats the lower mantle -> Creating convection currents.
-These hot, liquid magma currents ae thought to move in circles in the asthenosphere - thus causing the plates to move.
What is Palaeomagnetism?
-In the 1950s, studies of palaeomagnetism confirmed that sea floor was spreading. Every 400,000 years or so, the earth’s magnetic fields change direction i.e. the magnetic north and south pole.
-When lava cools and becomes rock, minerals inside the rock line up with the earth’s magnetic direction (polarity) at the time.
What is the Earth’s Crust?
-It is made of Oxygen, Silicon, Aluminium, Iron, Calcium, Sodium, Potassium and Magnesium.
-Beneath continents the earth’s crust can be 30-70 km and under oceans it is 5-7 km.
-The crust is solid and is 1000°c at the base.
What is the Lithosphere?
-It is made of rocks and minerals.
-The lithosphere includes the crust and the upper mantle so it’s about 100-300 km.
-The lithosphere is solid and is 300-500°c including the crust and upper mantle.
What is the Asthenosphere?
-It is the section of the mantle directly underneath the lithosphere.
-It is made of periodtite which is a rock containing mostly minerals olivine and pyroxene.
-It is about 200 km thick.
-It is solid that can behave like liquid and is 1,500°c.
What is the Mantle?
-It is made of mostly Iron, Magnesium, and Silicon.
-It is 3000 km thick, making it the thickest layer.
-It is a dense, semi-solid layer with temperatures of 1,000°c to 3,700°c.
What is the Outer Core?
-It is made of Iron and Nickle.
-It is about 2,200 km thick.
-It is liquid and ranges from 4,500-5,000°c
-It is mainly heated by radioactive decay of the element Uranium and Thorium which churns turbulent currents. This generates electrical currents which generate earth’s magnetic field.
What is the Inner Core?
-It is mostly made of Iron and Nickle making it extremely dense.
-It is about 1,200 km thick.
-It is solid and is about 5,200°c.
-The pressure is also well over 5 million times greater than the earth’s surface.
What is a Plate Boundary?
When two tectonic plates meet, plate boundaries are formed.
What are Plate Margins?
The areas adjacent (next to) the plate boundaries are plate margins.
What is an example of a Divergent Plate Boundary with continental crust?
The east-African rift valley.
What are Mid-Ocean Ridges?
A mid-ocean ridge is a seafloor mountain system formed by plate tectonics.
-New islands are formed
-Two oceanic crusts
-Submarine volcanoes
-Can extend for over 60,000 km
What are Rift Valleys?
-Two continental crusts
-Land collapses
-The crust stretches
-Faults form
What is the Subduction Zone?
Broad areas where two plates are moving together. Often the thinner, more dense oceanic plate descends beneath the continental plate.
What is a Locked Fault?
In a subduction zone, as plates move tigether they can get stuck due to frictional resistance. Such faults may store strain for extended periods, that is eventually released in a large magnitude earthquake.
What is the Benioff Zone?
An area of seismicity corresponding with the slab being thrust downwards in a subduction zone.
Describe the San Andreas Fault.
-It is located in California.
-The fault is 1,300 km long and is 25km deep.
-It makes the junction between the North American and Pacific Plates.
-It has a north west - south east trend in movement.
-Both plates are moving north west, the pacific plate is being moved north west due to the sea floor spreading -> the pacific plate is moving faster than the North American Plate, so the relative movement of the North Americna plate is to the south east.
Why is the San Andreas Fault a particular threat to the area?
-It has caused many large scale earthquake before and California is a very built up place with a large population meaning if there was an earthquake it would cause damage to a lot of infrastructure and so would costs a lot to repair or rebuild and so could cause a loss of jobs which would be bad for the local economy.
-It could also put lots of lives at risk and may cause people to have to re-house.
-It could also cause lots of disruption to wildlife and famous places like Santa Monica and San Diego.
How is the San Andreas Fault monitored and when do scientists predict the next big earthquake will occur?
In 2004 the National Science Foundation and the USGS started to drill a deep hole to install instruments within the fault zone. The instruments are 2-8 km below the earth’s surface.
->This will provide information on the composition and mechanical properties of rocks in the fault one, the nature of the stress responsible for the earthwuakes, the role of fluids in controlling faulting and earthquake recurrence and the physics of earthquake initiation and rupture.
What does Sinistral mean?
Movement to the left.
What does Dextral mean?
Movement to the right.
What is the Focus or Hypocentre of an Earthquake?
The point inside the crust from which the pressure is released.
What is the Epicentre of an Earthquake?
The point on the surface directly above Focus or Hypocentre.
What are Primary Waves?
-P waves are body waves (they travel through the Earth’s body).
-They are the fastest and the first to reach the surface (8km/sec).
-They travel through both solids and liquids.
-They move in a backwards and forwards motion.
-They are only damaging in the most powerful earthquakes.
