Chapter 3 Flashcards
What type of earth material is prone to liquefaction?
- artificial fill
- poorly consolidated sentiment
The second type of seismic wave to reach a recording station after an earthquake is called a ____ wave.
- shear
A seismometer must be installed in contact with ____.
- bedrock
P wave velocity depends upon the material through which the wave passes. Rank these materials from the fastest P velocity at the top
- 1) granite rock
- 2) packed sand
- 3) loose sand
- 4) water
- 5) air
To determine the _____ of an earthquake, seismologists use a nomograph, which compares the distance from the hypocentre and the amplitude of the seismic waves.
- magnitude
Seismic waves that pass through the interior of the planet are called ____ waves, whereas those that travel across the surface are called ____ waves.
- body
- surface
What phenomenon can cause liquefaction?
- earthquake vibrations
- rapid loading with excess weight
An earthquake occurs from the release of ____ when stress on a fault builds high enough for the rocks to fracture and move suddenly.
- energy
Which of the following describes a primary (P) wave?
- moves in a push-pull fashion
- the first to reach a recording station
- can travel through any material
Which of these correctly describe the nature of surface waves?
- slow moving
- low frequency
In which techtonic environment do deep earthquakes occur?
- subduction zones
What is a fault?
- a fracture in bedrock along which sliding has occurred.
The velocity of P waves depends on the ____ and ____ of the material through which they pass.
- density, compressibility
Because of their low frequency and slow speed, surface waves carry ____ amounts of energy away from the epicenter.
- large
What phenomenon can cause liquefaction?
- earthquake vibrations
- rapid loading with excdess weight
An earthquake of Richter magnitude 3 had a S wave amplitude of 1.2mm. What is the Richter magnitude of an earthquake with a S wave amplitude of 12mm, recorded at the same seismograph station?
- 4
The two types of body waves are ____ waves and _____ waves.
- primary
- secondary
The epicenter of an earthquake can be ____.
- underwater
Why does the difference in arrival times between P and S waves increase with epicentral distance?
- P waves travel faster than S waves
Place the four types of seismic waves in order of decreasing velocity, with the fastest at the top.
- P waves
- S waves
- Love waves
- Rayleigh waves
What might people have experiences during an earthquake of intensity IV?
- light sleepers woke up
In which techtonic environment do megathrust earthquakes occur?
- subduction zones
The acceleration due to gravity is ____, which is referred to as 1.0 g.
- 9.8 m/sec2
Because their motion is up and down and side to side, ____ waves are the type of body wave that can do severe damage to buildings.
- secondary
Love waves are a type of surface wave. They are similar to S waves in that they _____.
- cannot travel through fluids but can travel through solid material.
- travel with a shearing motion at right angles to their direction of advance.
Why was the 2010 Port-au-Prince earthquake so deadly?
- the general population and decision-makers lacked awareness of earthquake risk
- several buildings were poorly constructed
The rate of change in velocity of the ground as it is moved by seismic waves is called
- acceleration
What is the main cause of earthquakes?
- movements along faults
Which sections of the San Andreas fault have the highest seismic risk?
- locked zones
A ____ is a planar feature where the two rock blocks on either side move past each other.
- fault
If, during an earthquake, you feel like you’re being rocked in a boat at sea, you are most likely feeling the passage of ____ waves.
- Rayleigh
An earthquake occurring in which of the following geological environment will have the largest felt area?
- in the continental interior of North America.
Earthquakes are caused by a sudden fault rupture occuring
- at the hypocentre
P waves can travel through air, where they take the form of ____ waves.
- sound waves
How can you identify an aftershock?
- an aftershock has the same hypocentre as the main shock.
Acceleration during an earthquake is usually measured relative to ____.
- acceleration due to gravity
How many seismograms are required to locate the epicenter of an earthquake?
- a minimum of 3 seismograms from different stations
Charles Richter based his earthquake magnitude scale on the idea that _____.
- the bigger the earthquake, the greater the shaking of the earth.
What is the dominant deformation force associated with megathrust faults?
- shear
If a wave has a frequency of 20 Hz, what is its period?
- 0.05 s
What was the cause of the 2015 Nepal earthquake?
- the collision between the Indian and Eurasian Plates
Why are brace frames added to buildings?
- to reinforce the building against horizontal motions
Place the four types of seismic waves in order of decreasing velocity, with the fastest at the top.
- P waves
- S waves
- Love waves
- Rayleigh waves
Why don’t the rocks on either side of a fault simply slide past each other when stress is applied?
- friction holds the rocks together
If ten waves are recorded by a seismometer in one second, their frequency is:
- 10 Hz
The acceleration due to gravity is ____, which is referred to as 1.0g.
- 9.8m/sec2
What is a fault?
- a fracture in bedrock along which sliding has occured.
The San Andreas fault is ____.
- a complex system of subparallel transform faults.
How can you identify an aftershock?
- an aftershock has the same hypocentre as the main shock.
If local soil conditions were the same everywhere, how would the intensity contours look like on an isoseismal map?
- concentric circles
P waves travel through air, where they take the form of ___ waves.
- sound
In the pendulum seismograph, the pen ___.
- remains static with respect to the base
An isoseismal map displays contours of ____.
- intensity reported by eye witness.
Can you estimate the depth of the main magma chamber beneath Kilauea Volcano, Hawaii?
- 10 km
acceleration
- the rate of change of motion
aftershocks
- smaller earthquakes following a mainshock on the same section of the fault. Aftershocks can continue for years following a mainshock.
amplitude
- the maximum displacement above or below the undisturbed position; for example, the height of a wave crest or depth of a trough.
arrival time
- the time at which a seismic wave is detected by a seismograph
base isolation
- a system protecting buildings from earthquakes by isolating the base of the structure from the shaking ground via rollers, shock absorbers, etc.
body waves
- seismic waves that travels through the Earth. Primary (P) waves and secondary (S) waves are body waves.
creeping zone
- a section of fault where seismic energy is released frequently in small to moderate earthquakes.
felt area
- an area of perceptible earthquake ground motion.
foreshocks
- smaller earthquakes that precedes a mainshock on the same section as a fault.
fractures
- a general term for any breaks in rock
hertz (Hz)
- a unit of frequency. One hertz (Hz) equals one cycle per second.
inertia
- the property by which matter will remain at rest unless acted on by an external force.
isoseismal maps
- maps that uses contour lines to represent areas of equal Mercalli intensity.
liquefaction
- the temporary transformation of water-saturated loose sediment into a fluid typically caused by strong earthquake shaking
locked zone
- a section of a fault that has not released seismic energy for along time
mainshock
- the largest earthquake in a sequence.
megathrust earthquakes
- very large earthquakes that occur when stress accumulates at the contact between a subducting plate and overriding plate.
natural frequency
- the frequency at which a mechanical system (e.g. a soil, a building) vibrates when disturbed.
period
- the length of time for a complete cycle of waves to pass; period = 1/frequency
primary (P) wave
- the first seismic wave to reach a seismometer. movement is by alternating push-pull pulses that travel through solids, liquids, and gas.
resonance
- a vibrating body moves with maximum amplitude when the frequency of an imposed external forcing function is the same as its natural frequency
retrofitting
- reinforcing or strengthening an existing building or other structure.
secondary (S) wave
- the second seismic wave to reach a seismometer. Movement occurs by shearing particles at right angles to the directing of propogation. S waves move through solids only.
seism
- an earthquake
seismic waves
- a general term for all vibrations generated by earthquakes
seismic-gap method
- a theory that states that earthquakes are expected next along those fault segments that have not moved for the longest time.
seismograms
- the records made by a seismograph
seismology
- the study of earthquakes and the Earth’s interior, based on the analysis of seismic data.
seismometers
- instruments hat detect Earth motions
surface waves
- seismic waves that travel along the Earth’s surface only. Love and Rayleigh waves are surface waves.
