2.3 C: Geology = the Changing Earth 2.3 Earthquakes Flashcards
What do geologists believe about ancient earthquakes and volcanoes in Alberta?
Intense earthquakes and volcanoes frequently occurred in Alberta hundreds of millions of years ago.
This suggests that the geological history of Alberta is shaped by significant tectonic activity.
What is necessary to understand the effects of earthquakes?
Observing the effects of earthquakes in modern times is necessary.
Historical data can provide context, but contemporary observations are crucial for understanding current seismic activity.
When did the second-largest earthquake ever recorded occur?
March 27, 1964, at 5:36 p.m.
This earthquake is known as the 1964 Alaska earthquake and had a magnitude of 9.2.
What was happening in Alaska around the time of the 1964 earthquake?
Most people were home from work or on their way home, and many businesses had closed early due to Good Friday.
This likely reduced the number of casualties during the earthquake.
What was the significance of the timing of the 1964 earthquake?
The timing coincided with Good Friday and the start of the Easter holiday, leading to fewer people being present in high-rise buildings.
This timing contributed to the lower impact on human life compared to what might have occurred on a regular weekday.
Fill in the blank: The 1964 Alaska earthquake is the _______ largest earthquake ever recorded.
second
The largest earthquake recorded was the 1960 Valdivia earthquake in Chile.
True or False: The 1964 Alaska earthquake occurred during a typical weekday with many people at work.
False
The holiday timing meant fewer people were in workplaces, which likely saved lives.
What natural phenomenon can create seismic waves that are recorded by a seismograph?
Man-made explosions
What event caused a seismograph in Alaska to go off the chart?
The Alaska Earthquake of 1964
What intense effect did the 1964 Alaska Earthquake have on the Earth?
Earth vibrated like a gigantic planetary bell
What changes were noticed by farmers in Alberta and Saskatchewan the day after the Alaska Earthquake?
Changes in the height of their well water
Where was the most property damage caused by the 1964 Alaska Earthquake?
Coastal areas of Alaska
Which city suffered the greatest amount of property damage during the 1964 Alaska Earthquake?
Anchorage
How many blocks of office and apartment buildings were destroyed in Anchorage due to the earthquake?
About 30 blocks
What type of school was completely destroyed by landslides during the Alaska Earthquake?
Government Hill Grade School
What type of landslides were particularly devastating as a result of the Alaska Earthquake?
Underwater landslides
The violent ground shaking during the Alaska Earthquake lasted for how long?
Three minutes
True or False: The effects of the 1964 Alaska Earthquake were only felt locally in Alaska.
False
What caused the Alaska Earthquake of 1964?
The motion of the Pacific Plate relative to the North American Plate
What is the boundary between the Pacific Plate and the North American Plate called?
Fault
What type of crust is the Pacific Plate made of?
Dense oceanic crust
What process occurs when the Pacific Plate is pushed under the North American Plate?
Subduction
What happens to the continental crust of southern Alaska due to subduction?
It is compressed and warped
What is stored in the deformed areas of rock during the subduction process?
Elastic potential energy
When does a break occur in the fault during the earthquake process?
When the stress becomes greater than the breaking strength of the rock
On what date did the Alaska Earthquake occur?
March 27, 1964
Define ‘crustal plate’
A large section of Earth’s crust that moves and interacts with other plates
Define ‘plate tectonics’
The theory explaining the movement of Earth’s crustal plates and their interactions
Define ‘seismic wave’
A wave of energy that travels through the Earth’s layers as a result of an earthquake
Why do urban areas usually suffer the greatest loss of life as a result of earthquakes?
Higher population density and infrastructure vulnerability
Fill in the blank: The _____ is a crack in Earth’s crust due to the motion of one tectonic plate relative to another.
fault
Fill in the blank: _____ is the downturning of oceanic crust under another crustal plate.
Subduction
What is the process called when one tectonic plate moves under another?
Subduction
Subduction leads to geological changes such as earthquakes and volcanic activity.
What happens to the continental crust during subduction?
It is compressed and warped by pressures between tectonic plates
This deformation can cause significant geological transformations.
What type of energy is stored in deformed rock during tectonic stress?
Elastic potential energy
Similar to energy stored in a compressed spring, this energy can be released suddenly.
What occurs when stress on rock exceeds its breaking strength?
A break occurs in the fault
This results in the sudden release of stored energy.
On what date did the stress between the tectonic plates in Alaska get relieved?
March 27, 1964
This date marks the occurrence of the Alaska Earthquake.
What was the average distance that portions of southern coastal Alaska moved during the 1964 earthquake?
About 9 m
This movement was a result of the tectonic shift during the earthquake.
What are seismic waves?
Energy waves sent out from the lurching crust during an earthquake
Seismic waves transfer energy to other points on Earth’s surface.
What is the focus of an earthquake?
The region that first breaks along a fault during an earthquake
It is located below the Earth’s surface.
What is the epicenter of an earthquake?
The point on Earth’s surface directly above the earthquake’s focus
The epicenter is crucial for locating the earthquake’s effects on the surface.
How deep is the focus of the 1964 Alaska Earthquake?
25 km below Earth’s surface
This depth indicates the location where the earthquake initiated.
What geographical features are associated with the tectonic plates involved in the Alaska Earthquake?
Pacific Plate, North American Plate, Aleutian Trench
These features are significant in understanding the tectonic activity in the region.
What is the role of technology in understanding subduction and earthquakes?
It allows visualization of the process and its effects
Educational tools and simulations can enhance comprehension of geological phenomena.
What are primary waves also known as?
P-Waves
P-Waves are the first seismic waves to arrive and travel the fastest.
How do primary waves (P-Waves) travel through materials?
By alternately compressing and expanding the matter
P-Waves are similar to low-frequency sound waves.
What types of materials can P-Waves travel through?
Solids, liquids, and gases
This ability allows them to reach the surface from the focus.
What are secondary waves also known as?
S-Waves
S-Waves are slower than P-Waves and are termed secondary waves.
What is the primary difference in movement between P-Waves and S-Waves?
P-Waves compress and expand; S-Waves vibrate up and down or left and right
This difference affects how they travel through different materials.
What types of materials can S-Waves travel through?
Only solids
S-Waves cannot pass through liquids and gases.
How do S-Waves affect the shape of rock?
They change the shape without changing the volume
This is due to the nature of how S-Waves vibrate the rock.
Which type of seismic wave has a larger amplitude?
S-Waves
S-Waves transfer more energy than P-Waves due to their larger amplitude.
Define amplitude in the context of seismic waves.
The maximum displacement of a wave from the rest position
Amplitude is a key factor in determining the energy transferred by a wave.
Fill in the blank: A primary wave is a seismic wave that travels through _______.
solids, liquids, and gases
P-Waves are known for their ability to pass through all three states of matter.
True or False: S-Waves can pass through liquids.
False
S-Waves cannot pass through liquids or gases due to their inability to resist shape change.
What type of wave is classified as a longitudinal wave?
P-wave
A P-wave is characterized by particle vibration parallel to wave direction.
How are S-waves classified in terms of wave type?
Transverse wave
An S-wave has particle vibration perpendicular to wave direction.
In a longitudinal wave, the vibration of the particles is _______ to the direction the wave is travelling.
parallel
This is the defining characteristic of longitudinal waves.
In a transverse wave, the vibration of the particles is _______ to the direction the wave is travelling.
perpendicular
This describes the motion of particles in transverse waves.
What hand motion models the creation of P-waves?
Moving hand parallel to wave direction
This simulates the compressions and expansions of P-waves.
What hand motion is used to model S-waves?
Moving hand perpendicular to wave direction
This illustrates the shear motion of S-waves.
What is the key difference between P-waves and S-waves?
Particle motion direction
P-waves have parallel motion; S-waves have perpendicular motion.
What influences the speed of a wave that travels through a spring?
Changing properties like tension in the spring
This concept is analogous to how seismic waves behave in Earth’s layers.
What layers comprise the Earth?
Crust, mantle, outer core, inner core
Each layer has different properties such as density, temperature, and pressure.
How do seismic waves behave as they pass through different layers of Earth’s interior?
They travel at different speeds
This is supported by evidence found by geologists.
What happens to the speed of P-waves and S-waves as depth increases?
The speed increases
This is due to changes in rock properties.
What causes waves to quickly change direction as they travel through the Earth?
Sudden changes in rock properties
This is similar to light waves bending as they enter a lens.
What is the region called where P-waves from an earthquake cannot be detected?
P-wave shadow zone
This phenomenon occurs due to the change in material composition at Earth’s center.
What conclusion did researchers reach regarding the P-wave shadow zone?
Earth’s center is composed of different material than the mantle
This conclusion is based on the behavior of seismic waves.
True or False: As seismic waves travel deeper into the Earth, they always travel faster.
True
This is generally observed in both P-waves and S-waves.
Fill in the blank: Sudden changes in rock properties cause waves to quickly change _______.
direction
This change in direction leads to phenomena such as the P-wave shadow zone.
What is a key characteristic of S-waves in relation to the Earth’s core?
S-waves do not move through liquids
This indicates that the outer portion of the Earth’s core must be liquid, as S-waves are not detected in that region.
What is the S-wave shadow zone?
A larger region where no direct S-waves are received
This occurs because S-waves cannot travel through the liquid outer core.
What would happen if Earth had a uniformly solid composition?
Both P-waves and S-waves would move in straight lines at a constant speed
There would be no bending and no shadow zones.
How do surface waves differ from P-waves and S-waves?
Surface waves do not travel through the interior of Earth
They move along the surface of Earth’s crust.
What type of motion do surface waves cause in the ground?
They cause the ground to move up and down and from side to side
This is similar to the motion of water waves affecting a boat.
What is the travel distance of surface waves compared to S-waves?
Surface waves do not travel far from the epicentre
They also travel slower than S-waves.
Fill in the blank: Surface waves move along the _______ of Earth’s crust.
surface
True or False: Surface waves travel faster than S-waves.
False
What is a primary feature of the motion of surface waves?
More complex than P-waves or S-waves
The complexity includes both vertical and horizontal ground movement.
What is a key characteristic of S-waves in relation to the Earth’s core?
S-waves do not move through liquids
This indicates that the outer portion of the Earth’s core must be liquid, as S-waves are not detected in that region.
What is the S-wave shadow zone?
A larger region where no direct S-waves are received
This occurs because S-waves cannot travel through the liquid outer core.
What would happen if Earth had a uniformly solid composition?
Both P-waves and S-waves would move in straight lines at a constant speed
There would be no bending and no shadow zones.
How do surface waves differ from P-waves and S-waves?
Surface waves do not travel through the interior of Earth
They move along the surface of Earth’s crust.
What type of motion do surface waves cause in the ground?
They cause the ground to move up and down and from side to side
This is similar to the motion of water waves affecting a boat.
What is the travel distance of surface waves compared to S-waves?
Surface waves do not travel far from the epicentre
They also travel slower than S-waves.
Fill in the blank: Surface waves move along the _______ of Earth’s crust.
surface
True or False: Surface waves travel faster than S-waves.
False
What is a primary feature of the motion of surface waves?
More complex than P-waves or S-waves
The complexity includes both vertical and horizontal ground movement.
What type of waves produce the most damage in an earthquake?
Surface waves
Surface waves are the waves that travel along the Earth’s surface and are responsible for the most destruction during an earthquake.
What are the two types of seismic waves that geologists are particularly interested in?
P-waves and S-waves
P-waves (primary waves) can travel through the Earth and are used for subsurface exploration, while S-waves (secondary waves) provide information about the Earth’s internal structure.
What is a common application of P-waves and S-waves?
Locating an earthquake’s epicenter
The difference in arrival times between P-waves and S-waves helps determine the distance to the epicenter.
Why do S-waves lag behind P-waves?
Due to the lower speed of S-waves
S-waves travel slower than P-waves, resulting in a time difference in their arrival at seismographs.
What does the time difference between the arrival of P-waves and S-waves indicate?
The distance between the seismograph and the epicenter
A greater time difference indicates that the seismograph is further from the epicenter.
How can the time interval between P-waves and S-waves be used in earthquake analysis?
To determine the Richter magnitude of an earthquake
The time interval, along with other values, aids in calculating the earthquake’s magnitude.
What is the Richter magnitude scale used for?
Categorizing and comparing earthquakes
The Richter scale quantifies the amount of energy released by an earthquake.
What Richter magnitude is considered barely detectable by people?
0
Earthquakes with a magnitude of 0 are typically not felt by humans.
What was the Richter magnitude of the Alaska Earthquake of 1964?
9.2
This earthquake was one of the most powerful recorded in history, second only to the Chilean earthquake of 1960.
What was the magnitude of the Chilean earthquake of 1960?
9.5
This earthquake is the most powerful ever recorded.
True or False: Earthquakes with larger magnitudes may have occurred before the development of the Richter scale.
True
The Richter scale was developed in the 20th century, so significant earthquakes prior to this time are not accurately measured on this scale.
Fill in the blank: The Richter magnitude measures the amount of _______ at its epicenter.
vertical ground motion
The Richter scale quantifies how much the ground moves vertically during an earthquake.
What is the definition of an earthquake’s epicenter?
The point on the Earth’s surface directly above the location where seismic activity originates.
What caused the damage to the fishing boat in Kodiak during the 1964 Alaska Earthquake?
A tsunami, not by ground movement.
True or False: Tsunamis are sometimes incorrectly referred to as tidal waves.
True
What geological event triggered the series of enormous seismic waves during the 1964 Alaska Earthquake?
The sudden movement of the sea as the Pacific Plate moved under the North American Plate.
What historical event do the oral traditions of First Nations people on Vancouver Island recall?
An earthquake that occurred on January 26, 1700.
Fill in the blank: The arrival of the resulting tsunami from the 1700 earthquake was accurately recorded in the historical records of _______.
[fishing villages along the east coast]
How do geologists suspect the 1700 earthquake originated?
Off the coast of Vancouver Island.
What time did the earthquake on January 26, 1700, reportedly occur?
About 9:00 p.m.
What do many geologists regard the oral accounts of First Nations people as?
Accurate oral accounts of an earthquake.
What is the Cascadia Megathrust Earthquake?
A significant earthquake event that geologists study, particularly related to the 1700 earthquake.
What causes earthquakes?
The sudden release of stored energy due to the motion of crustal plates.
This energy builds up over time and is released when one plate moves relative to another.
What are seismic waves?
Waves that travel through surrounding rock after the release of energy in an earthquake.
Seismic waves are a result of the sudden movement of tectonic plates.
What type of seismic wave travels the fastest?
Primary waves (P-waves).
P-waves are the first to arrive at a point on the Earth’s crust.
Which seismic waves tend to cause more damage?
Secondary waves (S-waves).
S-waves arrive after P-waves and can cause significant destruction.
What type of waves generally cause the greatest damage during an earthquake?
Surface waves.
Although they travel slower than P-waves, surface waves tend to have the most destructive impact.
How is the location of the epicenter determined?
Using data from at least three seismographs.
The information from these seismographs can be combined to pinpoint the epicenter.
Fill in the blank: The _____ measures the magnitude of an earthquake.
Richter scale
The Richter scale quantifies the size of earthquakes based on seismic activity.
