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Earthquake Flashcards

(132 cards)

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1
Q

Where do 95% of earthquakes occur?

A

Along tectonic plate boundaries

This indicates the regions where tectonic activity is most prevalent.

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2
Q

What is the point inside the crust from which pressure is released during an earthquake called?

A

Focus or hypocentre

This is the origin point of the seismic waves.

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3
Q

What is the point on the surface directly above the focus called?

A

Epicentre

This location typically experiences the most shaking and damage.

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4
Q

What are seismic waves?

A

Energy released during an earthquake that radiates from the focus like ripples

They are the means by which the energy of an earthquake travels.

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5
Q

What are primary and secondary waves classified as?

A

Body waves

They travel through the Earth’s body.

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6
Q

What type of waves are Love waves?

A

Surface waves

They travel along the Earth’s surface.

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7
Q

What device is used to measure seismic waves?

A

Seismometer

It detects and measures ground movement caused by seismic waves.

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8
Q

What two measurements do scientists use to assess earthquakes?

A

Magnitude and intensity

These measurements help evaluate the earthquake’s effects and energy.

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9
Q

What does magnitude measure in relation to earthquakes?

A

The amount of energy released at the epicentre

This quantifies the earthquake’s strength.

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10
Q

What is the preferred way to measure magnitude of earthquakes?

A

MMS (Moment Magnitude Scale)

It is preferred because it is accurate and better at measuring large earthquakes.

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11
Q

What does MMS measure?

A

Total energy released by an earthquake at the moment it occurs

This is called the seismic moment.

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12
Q

What are the factors that MMS uses to measure seismic moment?

A

Factors include:
* Size of seismic waves
* Amount of slippage or rock movement
* Area of the fault surface broken by the earthquake
* Resistance of the affected rocks

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13
Q

What is intensity in the context of earthquakes?

A

An earthquake’s effect on people, structures, and the natural environment

Intensity is often measured using the Modified Mercalli Intensity Scale.

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14
Q

What are intra plate earthquakes?

A

Earthquakes that occur in the middle of tectonic plates, far from margins.

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15
Q

Name a historical example of intra plate earthquakes.

A

The 1811-1812 earthquakes in central USA (New Madrid, Missouri) with a magnitude of 7.5.

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16
Q

Why do scientists believe intra plate earthquakes occur?

A

They occur as stresses are built upon ancient faults, causing them to become active again.

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17
Q

What are primary effects of an earthquake?

A

Effects that happen as a direct result of an earthquake such as:
* Ground shaking
* Crustal fracturing

Ground shaking causes buildings, bridges, roads, and infrastructure to collapse, leading to casualties. Crustal fracturing occurs when energy released causes the earth’s crust to crack.

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18
Q

What is ground shaking?

A

The shaking of the ground caused by an earthquake, leading to the collapse of structures and infrastructure

Ground shaking can result in injuries or fatalities for those nearby.

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19
Q

What is crustal fracturing?

A

When energy released during an earthquake causes the earth’s crust to crack, leaving gaps on the earth’s surface

This can lead to significant geological changes in the affected area.

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20
Q

What are secondary effects of an earthquake?

A

Effects that can cause as much or more damage than the initial shaking, including:
* Liquefaction
* Landslides and avalanches

Secondary effects often complicate recovery efforts and can lead to further destruction.

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21
Q

Define liquefaction in the context of earthquakes.

A

The violent shaking during an earthquake causes surface rocks to lose strength and become more liquid than solid

This affects the ability of subsoil to support building foundations, leading to structural instability.

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22
Q

What happens to buildings during liquefaction?

A

Buildings and roads can tilt or sink due to the loss of support from the subsoil

This can complicate rescue efforts and disrupt underground utilities.

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23
Q

What causes landslides and avalanches during an earthquake?

A

The ground shaking places stress on slopes, causing them to fail

This can lead to significant geological hazards following an earthquake.

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24
Q

What notable event occurred during the 2011 aftershock in Christchurch, New Zealand?

A

The magnitude 6.3 aftershock caused more damage and loss of life than the initial 2010 earthquake

This highlights the potential severity of aftershocks following major seismic events.

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25
What are aftershocks?
Aftershocks are smaller earthquakes that occur in the general area of the original earthquake as a result of the earth's settling down or readjusting along the fault that slipped during the main earthquake.
26
How does the size of the original earthquake relate to aftershocks?
In general, the larger the earthquake, the larger and more numerous the aftershocks.
27
What additional damage can aftershocks cause?
Aftershocks can cause additional damage, such as collapsing structures that were weakened by the initial earthquake.
28
Which aftershock caused more damage and loss of life than its initial earthquake?
The 2011 magnitude 6.3 aftershock that struck Christchurch caused more damage and loss of life than the initial 2010 earthquake.
29
Why did the 2011 aftershock in Christchurch cause more ground shaking?
The 2011 aftershock was shallow focused and was centered closer to the city.
30
Is it possible to accurately predict when or where an earthquake will strike?
No, there is no method to accurately predict when or where an earthquake will strike.
31
Where do most earthquakes occur?
Most earthquakes occur at plate boundaries.
32
What is the likelihood of another serious earthquake striking San Francisco in the next 30 years according to the US Geological Survey?
The US Geological Survey forecasts a 67% chance of another serious earthquake striking San Francisco in the next 30 years.
33
What do geologists focus on today to predict earthquakes?
Research today focuses on 'warning signs' called precursors which suggest a major earthquake is about to happen.
34
What is a precursor in the context of earthquakes?
A precursor is a warning sign, such as foreshocks, that suggests a major earthquake is about to happen.
35
What are foreshocks?
Foreshocks are small earthquakes that happen before a big one.
36
Have foreshocks been proven to reliably predict larger earthquakes?
No, none have proved to reliably predict larger earthquakes.
37
When did the 2015 Nepal earthquake occur?
At midday
38
What was the effect of the timing of the 2015 Nepal earthquake on the death toll?
Helped to reduce the death toll considerably
39
What was the population density situation in most of Nepal during the earthquake?
Fairly low population density
40
Which area experienced the worst damage during the 2015 Nepal earthquake?
Rural areas
41
Why is Nepal considered a vulnerable country?
One of the world's poorest countries
42
What was Nepal's GDP per capita ranking in 2016?
197th out of 229 countries
43
What type of infrastructure was severely damaged or destroyed during the earthquake?
Roads, bridges, and safe water supplies
44
Why did many buildings in Kathmandu collapse during the earthquake?
Not built to withstand earthquakes
45
What occurred after the initial earthquake that caused further destruction?
Many large aftershocks and nearly 100 smaller ones
46
What natural disaster was triggered by the earthquake that affected rural areas?
Landslides
47
How did the mountainous terrain of Nepal affect rescue efforts?
Created landslides that cut off rural areas
48
What challenges did Nepal's emergency services face after the earthquake?
Unable to cope with the level of destruction
49
Who did Nepal rely on for help after the earthquake?
International aid agencies
50
Fill in the blank: The earthquake created _______ that devastated many rural areas.
landslides
51
True or False: Most of Kathmandu's buildings were designed to withstand earthquakes.
False
52
What significant event caused a decline in tourism in Nepal?
The earthquake
53
How much did Nepal's economy lose after the earthquake?
US$5 billion
54
What percentage of Nepal's GDP was lost due to the earthquake?
About 25%
55
How much funding was needed for rebuilding work in Nepal?
US$6.6 billion
56
What was the primary source of funding needed for the rebuilding work in Nepal?
Almost all for foreign aid
57
What is the distance to the center of the Earth's core?
About 6500 km
58
What is the estimated temperature near the Earth's core?
Over 6000°C
59
How do scientists map the structure of the Earth?
Using evidence from seismic waves
60
What is the lithosphere split into?
7 major and 7 minor tectonic plates
61
What do tectonic plates move over?
The asthenosphere
62
What is the range of movement speed for tectonic plates?
2-15 cm/year
63
What drives the movement of plate tectonics?
Several processes including mantle convection and slab pull
64
What happens in mantle convection?
Heat from radioactive decay heats the lower mantle, creating convection currents
65
What do the convection currents in the asthenosphere cause?
The movement of tectonic plates
66
What happens to newly formed oceanic crust at mid-ocean ridges?
It becomes denser and thicker as it cools
67
What causes the oceanic crust to sink into the mantle?
Its own weight
68
Fill in the blank: The Earth's core is estimated to be about _______ km from the surface.
6500
69
True or False: Tectonic plates move at a constant speed.
False
70
What is subduction?
The process where one tectonic plate slides under another into the mantle, where it melts.
71
What question does sea floor spreading raise?
If new crust is being created, then the Earth should be expanding.
72
Why isn't the Earth expanding despite the creation of new crust?
Because new crust is being destroyed by subduction in another area.
73
What happens when two oceanic plates move towards each other?
One plate slides under the other into the mantle.
74
What is a subduction zone?
An area where one tectonic plate slides under another and melts in the mantle.
75
What are mid-ocean ridges?
Huge underwater mountain ranges formed at the middle of many oceans.
76
How are mid-ocean ridges formed?
When hot magma is forced up to the asthenosphere and hardens.
77
What does the new oceanic crust do during sea floor spreading?
It pushes the tectonic plates apart.
78
Fill in the blank: The process of creating new oceanic crust is called _______.
sea floor spreading
79
What are the three main layers of the Earth?
Core, mantle, crust ## Footnote The core consists of the inner and outer core, the mantle surrounds the core, and the crust includes oceanic and continental types.
80
What are the two parts of the core?
Inner core, outer core ## Footnote The inner core is solid and mostly consists of iron, while the outer core is semi-molten and consists of liquid iron and nickel.
81
Where is the inner core located?
At the very centre of the Earth ## Footnote The inner core is the hottest part of the Earth at about 6000°C.
82
What is the temperature range of the outer core?
4500°C - 6000°C ## Footnote The outer core is semi-molten and mostly consists of liquid iron and nickel.
83
Describe the mantle.
Surrounds the core; widest layer of the Earth; upper part solid, lower part semi-molten ## Footnote The semi-molten part of the mantle is referred to as the asthenosphere.
84
What are the two types of crust?
Oceanic crust, continental crust ## Footnote Oceanic crust is thinner and denser, while continental crust is older and thicker.
85
What is the thickness range of oceanic crust?
6-10 km thick ## Footnote Oceanic crust lies on ocean floors.
86
What is the typical thickness of continental crust?
45-50 km thick ## Footnote Continental crust makes up the Earth's landmasses and is less dense than oceanic crust.
87
What do the crust and mantle together form?
Lithosphere ## Footnote The lithosphere is a solid layer that forms the tectonic plates.
88
True or False: The inner core is liquid.
False ## Footnote The inner core is solid and consists mostly of iron.
89
Fill in the blank: The outer core consists mostly of _______.
Liquid iron and nickel ## Footnote The outer core is semi-molten, contributing to the Earth's magnetic field.
90
What is palaeomagnetism?
The study of past changes in the earth's magnetic field ## Footnote Palaeomagnetism helps in understanding the history of the Earth's magnetic field and plate tectonics.
91
What occurs at a convergent boundary?
When 2 plates collide, also known as destructive margins ## Footnote Convergent boundaries can lead to the formation of mountains, earthquakes, and volcanic activity.
92
What is a divergent boundary?
Where 2 plates move apart, also known as constructive margins ## Footnote Divergent boundaries are typically associated with mid-ocean ridges and seafloor spreading.
93
What characterizes a conservative boundary?
Where 2 plates slide past each other, known as transform margins ## Footnote Conservative boundaries can cause earthquakes but do not typically result in volcanic activity.
94
What are convergent boundaries also known as?
Destructive plate margins
95
What occurs at a convergent boundary where an oceanic plate meets a continental plate?
The oceanic plate slides beneath the continental plate until it melts in the mantle
96
What marks the location where oceanic plates start to sink beneath continental plates?
Deep ocean trenches
97
What geological feature is formed from the convergence of oceanic and continental plates?
Fold mountains
98
What happens to the continental plate as two plates converge?
It is folded and pushed up, forming chains of fold mountains
99
What zone is associated with the friction created between colliding plates?
Benioff zone
100
What type of earthquakes occur in the Benioff zone?
Intermediate and deep earthquakes
101
What geological activity is generated by the melting oceanic plate?
Volcanic eruptions
102
What type of boundary occurs when two oceanic plates collide?
Subduction zone
103
What happens to the denser or faster oceanic plate during a collision of two oceanic plates?
It is subducted beneath the other
104
What forms where two oceanic plates collide and one is subducted?
Deep ocean trenches
105
What geological feature is formed from the rising magma after subduction of oceanic plates?
Underwater volcanoes
106
What are the separate island volcanoes formed from underwater volcanoes called?
Island arcs
107
What type of earthquakes are produced by subduction of oceanic plates?
Shallow and deep focus earthquakes
108
What event was caused by an earthquake resulting from the convergence of two oceanic plates in 2004?
The Indian Ocean tsunami
109
Fill in the blank: When oceanic plate meets continental plate, the oceanic plate is _______.
denser than continental
110
What occurs when two continental plates meet?
A collision margin occurs
111
Why are neither of the continental plates subducted when they collide?
Both plates have about the same density and are less dense than the asthenosphere beneath them
112
What geological features are formed as a result of continental plate collision?
High fold mountains, like the Himalayas
113
What type of earthquake focus is likely when continental plates collide?
Shallow focus
114
What are divergent boundaries also known as?
Constructive plate margins
115
What happens at divergent boundaries?
Two plates move apart, leading to the formation of new crust
116
What geological features do divergent boundaries form in oceans?
Mid ocean ridges
117
What geological features do divergent boundaries form on continents?
Rift valleys
118
What are mid ocean ridges?
Underwater mountains that extend for over 60,000km across the world's ocean floors
119
What are transform faults?
Regular breaks that cut across mid ocean ridges as they spread at different rates
120
What geological activity occurs along mid ocean ridges?
Regular volcanic eruptions create submarine volcanoes
121
What is an example of a new island formed by volcanic activity along a mid ocean ridge?
Iceland on the mid Atlantic ridge
122
What happens to the crust when plates move apart on continents?
The crust stretches and breaks into sets of parallel cracks (faults)
123
What are rift valleys?
Steep sided valleys formed when land between faults collapses
124
What occurs at conservative plate margins?
Two plates slide past each other ## Footnote This movement forms a conservative plate margin.
125
What is the result of the movement of plates at a conservative boundary?
A major break in the crust ## Footnote This break is known as a fault.
126
What is a fault?
The break itself where two plates move past each other ## Footnote A fault can occur on a larger scale, known as a transform fault.
127
What is a transform fault?
A fault that affects a wider area ## Footnote Transform faults are related to conservative plate margins.
128
What happens when the two plates at a conservative boundary stick?
Stress and pressure build up ## Footnote This buildup can lead to a sudden release of energy.
129
What is released when stress and pressure are suddenly released at conservative plate margins?
Seismic waves ## Footnote This release can cause shallow focus earthquakes.
130
Name one of the most famous conservative plate margins.
San Andreas Fault ## Footnote The San Andreas Fault is located in California and has generated significant earthquakes.
131
True or False: Conservative plate margins are associated with the creation of new crust.
False ## Footnote Conservative plate margins do not create new crust; they involve sliding past each other.
132
Fill in the blank: The major break in the crust caused by plate movement is called a _______.
fault ## Footnote Faults can lead to significant geological activity.

Tectonics (6 decks)

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