Earthquakes Flashcards by Emma Schmidt

What is the definition of a earthquake

the vibration generated by the
sudden release of energy associated
with the rapid movement of rock
along a fault

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Define a fault

*A fracture (or series of fractures) in the Earth’s crust
*Can occur at locations in the crust where rocks are
under stress and break
*Can also describe the boundary between two plates

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What are the features of faults

Epicenter, Fault surface, Focus, Seismic waves, Footwall, hanging wall

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What is an epicenter

a location on
the Earth’s surface
directly above the focus.

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What is a fault surface

the
fracture surface between
one block and another
along which movement
occurs

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What is the focus

‘origin’ of the
earthquake. The point
within the Earth’s crust
where movement first
occurred

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What are seismic waves

waves
of energy that travel
like shock waves from
the focus to the
surrounding area

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What are the two most important kinds of seismic waves

P-waves and S-waves

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Describe the motion of a P-wave

This is a type of compression wave. Imagine a slinky and your hand is motion it left and right, so the slinky becomes compressed. The wave travels in the same path of motion as your hand does.

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Describe the motion of a S-wave

This is a shear wave. The hand motion travels up and down and the wave travels left with it looking like a sine wave.

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What are the three main kinds of faults + one that is another variation of the reverse fault.

Strike-slip fault, Normal Fault, Reverse Fault
Thrust fault are low-angle reverse faults

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Is the strike slip tension or compression?

Shearing tension - pulling in opposite directions along a plane

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Is the Normal fault tension or compression and where would we expect to see it

Tension
occurs mainly at divergent plate boundaries

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Is a thrust fault tension or compression and where would we expect to see it

Compression
Convergent plate boundary

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Is a reverse fault tension or compression and where would we expect to see it

Compression
Convergent plate boundary

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How do we measure earthquakes

Seismometers and seismographs

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________ ________ are detected by an instrument called a seismometer and recorded as a paper or electronic trace known as a ____________

Seismic waves
Seismogram

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Earthqaukes often occur in clusters.
What is the name to describe each of these definitions
1. Biggest earthquake in the cluster
2. occurs before the main shock
3. occurs after the main shock

Main shock
Foreshock
Aftershock

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Prior to the earthquake the _____________ foci are close to the focus.
After the earthquake the _____________ foci travel away from the focus

Foreshock
aftershock

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What are the scales we use to measure earthquakes

Moment magnitude scale (Mw)
Logarithmic scale

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What scale did the moment magnitude scale replace

Richter scale

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Identify each of the scales as quantitative and qualitative
Richter scale
Moment magnitude
Modified Mercalli intensity scale
Peak ground acceleration

Richter Scale: the oldest and best known, quantitative

Moment Magnitude (Mw
): used by seismologists, quantitative

Modified Mercalli Intensity Scale: qualitative

Peak ground acceleration: not a scale technically, used by
engineers, quantitative, site specific

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What is the Richter magnitude calculations based on

difference between P and S wave arrival times
maximum seismic wave amplitude on a seismograph

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Limitations of Richter Magnitude

Not accurate for describing large earthquakes (8 or greater)
Not accurate for deep earthquakes or earthquakes a long way
away from the seismograph station

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The moment magnitude is based on _______ ________

energy released

The moment magnitude is similar values to ______ _______ for small to large earthquakes. However, the Moment magnitude is a more precise scale for measuring magnitude larger than __

Richter Magnitudes 8

What are the measurements used to determine the moment magnitude

based on seismograph measurements and measurements of fault displacement

How is peak ground acceleration measured and what do the measurements depend on

Using an accelerogram the maximum ground acceleration during an earthquake, in horizontal and vertical directions measures ground shaking at a specific location - not magnitude of the earthquake These measurements depend on the local geology (sand shakes more than solid rock)

What does PGA represent

Peak Ground Acceleration

Seismic risk maps present what?

Seismic risk maps present expected PGA values for a region if an earthquake were to occur

What is the modified Mercalli intensity scale based on

This scale is based on observations and perceptions of people who felt the earthquake, therefore it is subjective (based on personal experience) and qualitative.

How many degrees of intensity does the modified Mercalli intensity scale have? What do they depend on?

12 The degree of intensity will vary depending on where the earthquake occurs

For these descriptions, which is a 1 on the modified Mercalli intensity scale and which is a 12 Detected only by seismic instruments; causes no damage Earthquake waves cause visible undulations of the ground surface; objects are thrown up off the ground; there is complete destruction of buildings and bridges of all types

The first definition would be a 1, the second description is a 12

What are two websites you can report your expirince of a earthquake to then build a MMI map

Canada - NRCan website World - USGS website

What kind of sediments/rock shake more in an earthquake? Order these from Hard(least seismic wave amplification) to soft(most seismic wave amplification) Stiff soil(mud), Hard rock(igneous rock), Very dense soil and soft rock(sandstone), soils requiring site-specific evaluation(peat, some clays), Soft soil(artificial fill), Rock(volcanic rock)

Hard Rock Rock very dense soil and soft rock stiff soil soft soil soils requiring site-specific evluations

The softer the geological media (soil, rock, or sediment) under a building or structure, the _______ likely there will be a failure in an earthquake

Worldwide, _______ earthquakes happen more than once per month. _________ earthquakes, such as magnitude 2 earthquakes, occur several hundred times a day. To create a mountain system might take several million _________ sized earthquakes over tens of millions of years.

Strong Smaller Medium

What are natural causes for earthquakes

* creation of a new fault by rock fractures along a fault plane * movement along an old fault * movement of magma below the surface or a volcanic explosion * huge landslide

What are anthropogenic causes of earthquakes

*underground nuclear explosive tests *fracking - injections of water and sand *wastewater injection water pressure increases in inactive faults and pushes them apart btw, anthropogenic means human-made

Where are earthquakes concentrated in Canada

Along the west coast - plate tectonic boundaries several in Ontario and Quebec along old fault zones, a weakness in the crust

Why would earthquakes occur in northern Canada

Northern Canada may relate to retreat of glaciers 1000s of years ago - land slowly rising (was depressed by the glaciers)

What are the magnitude of earthquakes in Estevan and Radville

M4-M5, Iv - V Mercalli Due to rocks slowly dissolving at depth, shifting along faults.

Describe elastic rebound theory

* Energy is stored in the form of elastically deformed rock. * When strain exceeds rock strength, the rock fractures and energy is released

Stages of elastic rebound theory occurring

1. Curst at rest (no strain) 2. Crust deformed, strain accumulates (strain build up) 3. Ruptured crust causing earthquake (rupture with elastic rebound) 4. Fractured crust, Fault zone (strain released)

What is the elastic limit?

The breaking point

What occurs when you exceed the breaking point during an earthquake

The material will fracture

Earthquakes happen when the _______ _______ of the rock along a fault with accumulated stresses is __________

Elastic limit exceeded

The sudden release of energy, as the rock ‘snaps’ or fails, generates a series of ‘shock waves’ called ______ _______, that move through the rock

Seismic waves

Which of these statements are true: Stress - Force/area - elastic bending Strain - Force/area - elastic bending rupture - Force/area - elastic bending Stress - deformation - rupture formation Strain - deformation - rupture formation Rupture - deformation - rupture formation Strain - slip and vibration Stress - slip and vibration Rupture - slip and vibration

Stress - Force/area - elastic bending Strain - deformation - rupture formation Rupture - slip and vibration

Which type of waves travel through the earths interior and consist of P-waves and S-waves

Body waves

Which type of wave travels along the surface of the lithosphere and consist of love waves and Rayleigh waves

Surface waves

Seismic waves are detected by an instrument called a ____________. They contain several instruments that detect motion in different directions.

seismometer

The results are recorded as a paper or electronic trace known as a ______________. _____ waves arrive first, then ______ waves, then ______ waves.

seismogram P S Surface

How fast the waves travel depends on the rock they are travelling through – ________ materials, faster travel!

Harder

_________ is used to determine the layers inside the earth such as the crust, Mantle, and core

Seismology

The more consolidated / cemented the rock, or the denser the minerals in the rock, the ______ the speed of a wave

Faster

What is rarefraction

“bending” of the seismic waves as they move from one material to another of different density

Why is wave refraction used

is used to identify a discontinuity (change) e.g. a discontinuity in the rock density and/or composition

What is wave reflection

waves “bounce” off surfaces

If a wave travels from a less dense rock to a more dense rock, will the refracted wave be bent down or up?

Refracted wave bent up

If a wave travels from a more dense rock to a less dense rock, will the refracted wave be bent down or up?

Refracted wave bent down

Can S-waves and P-waves travel through solids and/or liquids?

S-waves travel through solids but not liquids P-waves travel through solids and liquids

Are s-waves or P-waves detected first at a seismic station?

P-waves

Are P-waves or S-waves analogous to sound waves?

P-waves

Are P-waves or S-waves faster?

P-waves

How many degrees is the P-wave shadow zone?

150 - 103 = 47 degrees

How many degrees is the S-waves shadow zone?

It begins at 103 degrees on both sides, waves cannot travel through the core of the earth.

Do P-waves or S-waves cause the most damage?

S-waves

_______ ________ confirm the existence of discontinuities in Earth’s interior

Seismic data

How can we tell there are discontinuities in the earths interior using seismic data

S waves are attenuated (stopped) by liquid outer core layer * P waves refract when they go from one layer to another and there is a change in composition * By studying seismic data at seismograph stations around the world, we can see the evidence for the Earth’s layers!

Describe the movement of love waves

cause horizontal shifting at the surface of the earth

Describe the movement of Rayleigh waves

rotating waves along surfaces, create vertical displacement (movement), like ripples on water

Divergent Boundaries: _______ earthquakes within ocean basins, foci are located: Along _______ _______ Along ________ ______

Shallow mid-ocean ridges transform faults

Transform-Fault boundaries: Transform faults along plate boundaries have _______ earthquakes _______ _______ mechanism due to shearing forces from tectonic plate movement. Can produce ______, _________ earthquakes

many strike-slip fault large, destructive

Convergent Boundaries: Largest earthquakes occur at __________ zones. -called __________ earthquakes -Overriding plate thrust _______ relative to the subducting plate The three _______ earthquakes ever measured by seismometers were of this type

Subduction megathrust upward largest

*Zone of seismicity along the plane of the subducting plate is called

the Wadati-Benioff Zone

The size or magnitude of an earthquake is related to

depth

___% of earthquakes occur at a depth less than 100 km

____ severe earthquakes are shallow earthquakes (focus is in the upper 70km)

Most

Are the focus depths off the west coast of BC shallow or deep?

Shallow

The subducting juan de fuca plate is at a very shallow angle. This creates a weak or strong earthquake?

Strong

Intense __________ of the plates where they collide, causes folding and faulting, thrust faults

compression

Earthquakes at ________-_________ __________ plate boundaries are generally shallow, spread over a wide area in the region compressed by the collision

continent-continent convergent

What is an example of a continent-continent convergence

Himalayas

What are the ways earthquakes cause damage

Faulting and shaking – primary hazards *Landslides *Liquefaction *Tsunamis *Fires

What does liquefaction mean

*Shaking causes water-saturated sediment to temporarily behave like a fluid *Friction decreases as water moves between particles *Particles consolidate and pore waters are expelled

Fill in the blanks for these characteristics of tsunamis: * Undersea megathrust earthquakes often generate __________ waves * Thrust faulting leads to ______ seawater displacement, forms water wave * Waves travel ________ from epicenter, when reach shore slow down and amplify vertically

destructive vertical outward

A tsunami is only a few _________ high in the deep ocean but can _________ to _______ _______ high close to shore

centimeters increase many meters

The more consolidated/cemented the rock, the ______ the speed of a wave

faster

As speed decreases, wave amplitude _________ and so does the potential for damage

increases

Where is seismic risk higher

*Delta sediments *Floodplain sediments *Mountain slopes *Saturated materials *Thicker sediments

anthropogenic causes of earthquakes

mining, injecting water, oilfield activity

Earthquakes Flashcards

(92 cards)