final exam written q examples Flashcards
EARTH’S STRUCTURE & TECTONICS
How is it that the compositions of certain types of meteorite represent the bulk composition of planet Earth?
Approximately what age are these meteorites?
Draw two diagrams, each depicting a cross section through the solid Earth’s interior.
(a) On one diagram, label the major rheological layers stating the basic rheology of each one.
(b) On the other diagram, label the Earth’s main compositional layers, stating the basic chemical composition of each one
(a) Describe the major differences between oceanic crust and continental crust in terms of their composition and physical properties.
(b) Show how these differences explain the contrast in deformation observed at ocean-continent convergent plate boundaries (subduction zones), versus continent-continent convergent plate boundaries (continental collisions)?
What are coronal mass ejections, and how do they cause geomagnetic storms?
Describe a few of the human impacts of these event
Describe one piece of geological evidence in support of the theory of continental drift and one piece of geophysical evidence used to develop the theory of plate tectonic
Which bathymetric features (bathymetry = sea floor topography), mapped using sonar initially during the Second World War, were later used in the development of the theory of Plate Tectonics?
Illustrate by drawing a schematic cross-section of an ocean-ocean divergent plate boundary and an ocean-continent convergent plate boundary.
MC
What is the difference between continental and oceanic crust in terms of density?
Continental crust is denser than oceanic crust.
They have, on average, the same density.
Oceanic crust is denser than continental crust.
What is the typical geothermal gradient in Earth’s lithosphere?
2.5ºC per kilometer
25ºC per kilometer
250ºC per kilometer
2500ºC per kilometer
How long do coronal mass ejections take to travel from the Sun to the Earth?
From ∼1 second up to a few seconds
From ∼1 minute up to a few minutes
From ∼1 hour up to a few hours
From ∼1 day up to a few days
What are the origins of the Earth’s internal heat?
Accretion of material forming the proto-Earth.
Frictional heating during Earth’s differentiation.
Radioactive decay of radioactive elements within the Earth.
All of the above.
What are the main mechanisms for heat transfer through (a) the lithosphere and (b) the asthenosphere/mesosphere?
(a) Convection; (b) Convection
(a) Conduction; (b) Convection.
(a) Conduction; (b) Conduction.
(a) Convection; (b) Conduction.
How do the Earth’s crust and lithosphere relate to one another?
The crust contains the lithosphere plus part of the asthenosphere.
Crust and lithosphere are compositional and rheological terms for exactly the same part of the Earth.
The lithosphere contains the crust plus part of the upper mantle.
What was the Tunguska event?
The most recent reversal of Earth’s geomagnetic poles
An intense geomagnetic storm caused by a massive coronal mass ejection
An air burst due to a large meteor exploding in the atmosphere
A cratering impact event
What rock type is the upper mantle made of?
Basalt
Granite
Sedimentary rock
Peridotite
Which class of meteorite describes undifferentiated planetary material?
Chondrites
Iron meteorites
Achondrites
Stony-iron meteorites.
How is Earth’s age of 4.56 billion years known?
From radiometric dating of chondrite meteorites.
From radiometric dating of the oldest known continental crust.
From radiometric dating of the oldest known oceanic crust.
From calculating the time needed for Earth to cool to its present temperature from an initial molten state.
From counting tree rings at the time of the dinosaurs
MC
Why does melting occur at mid-ocean ridges?
Due to higher water content of the mantle.
Due to structural weakness of the crust.
Due to lower mantle pressure.
Due to higher mantle temperatures.
The Yellowstone hot spot track suggests that the North America plate is moving in which direction?
Towards the north-east.
Towards the south-west.
Towards the north-west.
No direction - it implies that the North America plate is stationary.
How can hot spots be used as evidence for plate tectonics?
They indicate how the plate has moved over the stationary mantle plume.
Hot spots are evidence against plate tectonics.
They explain why volcanoes occur above subduction zones.
They indicate how the mantle plume has moved beneath the plate
What is a passive continental margin?
A tectonically inactive plate boundary.
A transition from oceanic to continental crust within the same plate.
An ancient rift attempt that failed to establish a sustained spreading centre.
Any transition from oceanic to continental crust whether or not it is a plate boundary.
How do you envisage the seismic risk changing in Victoria, BC, over the next fifty years?
Make reference both to the expected rapid population growth, and also to the potential to improve earthquake mitigation and/or preparedness.
What type of plate boundary does the San Andreas fault represent?
A continental strike-slip boundary.
A continental rift.
A continental collision.
A subduction zone.
Victoria is situated closest to the boundary between which tectonic plates?
The triple junction between the North American, Pacific, and Juan de Fuca plates.
The boundary between the North American and Juan de Fuca plates.
The boundary between the North American and Pacific plates.
The boundary between the Pacific and Juan de Fuca plates.
Which ocean is characterized by passive continental margins on both sides?
The Indian Ocean.
The Atlantic Ocean.
The Pacific Ocean.
Why does melting occur at subduction zones?
Due to lower mantle pressure.
Due to structural weakness of the crust.
Due to higher mantle temperatures.
Due to higher water content of the mantle.
Why does melting occur at hot-spots?
Due to higher mantle temperatures.
Due to lower mantle pressure.
Due to higher water content of the mantle.
Due to structural weakness of the crust.
What is the relationship between the theories of continental drift and plate tectonics?
Continental drift provides the physical mechanism to explain plate tectonics.
Plate tectonics and continental drift are rival theories that are mutually exclusive.
Continental drift and plate tectonics are different terms for the same thing.
Plate tectonics provides the physical mechanism to explain continental drift.
EARTHQUAKES
(a) What are the three basic types of fault, and how do they differ?
(b) Which type of fault is responsible for the largest (Mw>8) great earthquakes?
(c) What tectonic setting are these great earthquakes restricted to, and why?
What are the main types of seismic wave?
Discuss the basic characteristics of each, in terms of their path, velocity, particle motion, and potential to cause damage.
Explain in principle (no need to include any math) how the difference in seismic wave speeds can be:
(a) used to locate an earthquake?
(b) used to provide early warning of imminent ground shaking (“Earthquake Early Warning”)
What are the basic differences between the earthquake magnitude and intensity scales?
Use a real earthquake case study to illustrate one of the major factors that determines intensity.
List some of the factors which control the peak intensity felt during an earthquake.
Why are seismic risks increasing through time, even as our understanding of earthquakes improves?
Briefly, what accounts for the large number of devastating earthquakes in the country of Iran (for example, the 2003 Mw 6.6 Bam earthquake)?
Briefly explain why in some earthquakes, buildings of a certain height are destroyed, whereas buildings that are shorter or taller withstand the shaking.
You may like to use a recent case study to illustrate.
(a) Briefly explain on what kind of geological structures intraplate earthquakes are found.
(b) What are some of the possible driving forces behind intraplate earthquakes.
(a) Below is a map of the tectonics of Cascadia. Sketch a simple diagram (not to scale) showing a cross-section of the structure along the line A-A’ indicating oceanic and continental crust, man- tle, lithosphere and asthenosphere; labelling tectonic plates and plate boundaries; and indicating directions of motion.
(b) With reference to your cross-section, what are the three major sources of seismic hazard in this region? How do they differ in terms of the likely earthquake magnitude, depth, and distance from population centres?
MC
How do earthquake seismograms recorded at larger epicentral distances differ from those recorded at shorter epicentral distances?
At larger epicentral distances, the S waves will arrive on the seismogram before the P waves do.
At larger epicentral distances, the P wave, S wave and surface wave arrivals will be more separated on the seismogram.
At larger epicentral distances, the P wave, S wave and surface wave arrivals will be more closely spaced on the seismogram.
At larger epicentral distances, no surface waves will appear on the seismogram.
The photo below shows a surface rupture from a recent earthquake in Taiwan (crossing the athletics track in the middle of the photo). What was the mechanism of this earthquake?
Reverse
Normal
Right-lateral strike-slip
Left-lateral strike-slip
What is the earthquake cycle?
The cyclic build-up and release of stress and strain on a fault.
The life cycle of an oceanic normal fault, from when it is formed at a mid-ocean ridge to when it is destroyed through subduction.
The duration of a single earthquake rupture, from when it starts to slip to when it stops slipping.
The return period between large earthquakes as felt at a given location.
At which of the following types of plate boundary are reverse/thrust faults most common?
Subduction zones and continental collision zones.
Mid-ocean ridges and continental rifts.
Continental shear zones.
What type of strain do normal faults accommodate?
Simple shear
Contraction (shortening)
Extension
What best describes earthquake body waves, which travel through the Earth’s interior, in relation to surface waves, which travel around the Earth’s surface?
Body waves are faster and larger amplitude.
Body waves are faster and smaller amplitude.
They travel at the same velocity, but body waves are larger amplitude.
Body waves are slower and larger amplitude.
Body waves are slower and smaller amplitude.
What is the name given to faults that accommodate both vertical and lateral slip?
Oblique slip faults
Mixed mode faults
Splay faults
Bilateral faults
What best describes particle motion during the passage of a P-wave?
Compression/tension in the direction that the P-wave travels.
Compression/tension perpendicular to the direction that the P-wave travels.
Shear in the direction that the P-wave travels.
Shear perpendicular to the direction that the P-wave travels.
The photo below shows a surface rupture from a recent earthquake in Italy. What was the mechanism of this earthquake?
Reverse
Normal
Right-lateral strike-slip
Left-lateral strike-slip
What type of faulting results in crustal thickening?
Normal faulting.
Left-lateral and right-lateral strike slip faulting.
Reverse/thrust faulting.
Left-lateral strike slip faulting.
Right-lateral strike-slip faulting.
MC - prt 2
What factors could influence the shaking intensity felt during an earthquake at a given location?
The magnitude of the earthquake.
The type of rock in that location (e.g. soft sediment, hard bedrock)
The depth of the earthquake.
The distance to the earthquake epicenter.
All of these factors would influence the felt intensity.
The photo shows fracturing of a road caused by a large earthquake in Alaska. Which phenomenon explains why road damage seems to be restricted to the causeway across a low-lying marshy area?
The rupture directivity effect
Earthquake surface rupturing
The basin amplification effect
Liquefaction of water-saturated sediment
Given two earthquakes of the same magnitude and depth, one in western North America and one in eastern North America, which will likely be felt over a wider area and why?
Neither will be felt over a wider area, since two earthquakes of the same magnitude and depth will always produce identical patterns of ground shaking
The earthquake in western North America will be felt over a wider area because the western half of the continent contains a much greater density of active faults
The earthquake in eastern North America will be felt over a wider area because of thick sediments underlying the eastern North American passive margin
The earthquake in eastern North America will be felt over a wider area because of the stronger (less fractured) geology underlying the eastern half of the continent
The largest magnitude earthquakes are:
Strike-slip earthquakes.
Subduction megathrust earthquakes.
Normal fault earthquakes at mid ocean ridges.
Reverse fault earthquakes in continental collisions.
How can the dip angle of the fault influence the magnitude of an earthquake?
Shallow-dipping faults rupture more slowly than steeply-dipping faults, generating smaller magnitude earthquakes.
Shallow-dipping faults have a larger surface area within the brittle upper crust than steeply-dipping faults, giving them greater potential for larger magnitude earthquakes.
Shallow-dipping faults naturally slip more than steeply-dipping faults, generating larger magnitude earthquakes.
Shallow-dipping faults naturally slip less than steeply-dipping faults, generating smaller magnitude earthquakes.
In the equation for seismic moment, what does the shear modulus describe?
It describes a material’s resistance to deformation by shear stress — or put more simply, its stiffness.
It describes the area of fault that ruptures in an earthquake.
It describes the average slip in an earthquake.
Why do sedimentary basins amplify incoming seismic waves (basin amplification)?
Because seismic waves slow down as they pass into loose sedimentary rocks.
Because seismic waves speed up as they pass into loose sedimentary rocks.
Because water-saturated sedimentary rocks liquefy during ground shaking.
Which statement best describes earthquake frequency-magnitude relations?
For each unit increase in moment magnitude, there are about ten times more earthquakes.
For each unit increase in moment magnitude, there are about twice as many earthquakes.
For each unit increase in moment magnitude, there are about half as many earthquakes.
For each unit increase in moment magnitude, there are about ten times fewer earthquakes.
How much more seismic moment is there in a Mw 6.0 earthquake than in a Mw 5.0 earthquake?
6/5 = 1.2 times as much.
10 times as much.
(6/5) x 10 = 12 times as much.
101.5 = 32 times as much.
What is the truest measure of the energy released by an earthquake?
Its maximum intensity on the Mercalli scale.
Its seismic moment.
Its Richter scale magnitude.
Its rupture velocity (the speed at which the earthquake propagates along the fault).
MC. - prt 3 (case studies)
Which aspects of the 2011 Mw 9.0 2011 Tohoku earthquake took scientists by surprise?
Its rupture area, average slip, and moment magnitude were all much greater than expected.
It generated a larger tsunami than was anticipated.
It slipped all the way to the surface (the sea-floor at the trench).
All of the above.
During the interseismic period preceding the 2011 Mw 9.0 Tohoku earthquake, in which direction did the eastern coastline of the main Japanese island of Honshu move?
Westwards and upwards (uplift).
Eastwards and downwards (subsidence).
Eastwards and upwards (uplift).
Northwards and downwards (subsidence).
Intraplate earthquakes in eastern Canada are mostly associated with which geological feature(s)?
The Canadian Shield.
Failed rifts and the North Atlantic passive margin.
Faults and folds of the Appalachian mountain belt.
The Sudbury and Manicouagan impact craters.
What is a postglacial earthquake?
An earthquake caused by bending stresses following the melting of ice sheets and glaciers.
Any earthquake that occurred during the Holocene (i.e., since the end of the last Ice Age).
A fracture caused by thawing of the ground surface following the melting of ice sheets and glaciers.
An earthquake caused by shearing stresses from the flow of glaciers over the Earth surface.
Which of the following statements about the Iranian capital city of Tehran is true?
Tehran was badly damaged in the 2003 Mw 6.6 Bam earthquake.
Fortunately, Tehran lies within an area of Iran that is not thought to be at risk from earthquakes.
Tehran has no historic record of earthquakes, but modern seismic instrumentation detects abundant seismicity there.
Tehran has experienced several large earthquakes in its recorded history, but none since it grew into a large metropolis.
Which of the following regions within Cascadia is most closely associated with intermediate depth “intraslab” earthquakes?
Northern Vancouver Island.
The Lower Mainland region of BC.
Southern Vancouver Island.
The Puget Sound region in Washington State.
Which of the following U.S. States is closely associated with induced seismicity?
Oklahoma.
California.
Florida.
Alaska.
Hawaii.
Along some parts of some faults, the two sides move past each other slowly, and continuously, without the stick-slip behaviour associated with earthquakes. What is the name given to this slow and steady fault motion?
Fault creep.
Poro-elastic rebound.
Visco-elastic relaxation.
Interseismic deformation.
Iran occupies the boundary zone between which two tectonic plates?
Africa and Eurasia.
Arabia and Africa.
Arabia and Eurasia.
India and Eurasia.
During the 2011 Mw 9.0 Tohoku earthquake, in which direction did the eastern coastline of the main Japanese island of Honshu move?
Eastwards and downwards (subsidence).
Northwards and upwards (uplift).
Westwards and downwards (subsidence).
Westwards and upwards (uplift).
MC - more case studies
What is the engineering term for decoupling/disconnecting a building from the ground, in order to reduce its vibration in an earthquake?
Base isolation.
Seismic retrofitting.
Surface wave reduction.
Resonance.
Complete the sentence: earthquake prediction is…
… currently impossible.
… currently possible, but only for earthquakes with foreshocks.
… currently possible, but only in certain parts of the world.
… currently possible, but only for the largest earthquakes.
‘There is a ~12% to ~33% chance of a megathrust earthquake on the Cascadia subduction zone in the next fifty years.’ This statement is an example of what?
An earthquake early warning.
An earthquake forecast.
A seismic retrofit.
An earthquake prediction.
What is the central aim of the U.S. Geological Survey’s PAGER program?
To map damage in each major earthquake from across the United States using satellite radar measurements
To map damage in each major earthquake from around the world using satellite radar measurements
To issue to users (e.g. scientists, emergency responders) a rapid alert to each earthquake above a threshold magnitude of 3 from across the United States
To issue to users (e.g. scientists, emergency responders) a rapid alert to each earthquake above a threshold magnitude of 4 from around the world
To estimate very rapidly the damage (in terms of both fatalities and economic costs) caused by each major earthquake from across the United States
To estimate very rapidly the damage (in terms of both fatalities and economic costs) caused by each major earthquake from around the world
