ESCI 1001 Midterm (Lecture 5)

What is an earthquake?

Earth shaking caused by a rapid release of energy; happens due to rocks breaking from tectonic plate stress.

What is seismicity?

Earthquake activity/frequency.

What is a fault?

An extended break in a body of rock, marked by the relative displacement and discontinuity of strata on either side of a particular surface.

What are Love (L) waves?

Secondary waves that intersect the surface.

What are Rayleigh waves?

Primary waves that intersect the surface.

What is the footwall?

The block below the fault.

What is the hanging wall?

The block above the fault.

What is a thrust fault?

A reverse fault with a dip of 45 degrees or less.

A special type of reverse fault where the slope (dip) of the fault surface is not steep.

What is an oblique-slip fault?

Fault that moves parallel to the dip of the fault plane.

A combination of 'dip' fault and strike-slip displacement, most faults display some sort of oblique-slip character, pure 'dip' or strike-slip faults are rare

What is stick-slip?

Rupture along a fault occurs by fits and starts, usually in a sporadic motion.

What are body waves?

Waves that can travel through the Earth's inner layers.

What are surface waves?

Waves that can travel along the Earth's surface. They are also the third waves to arrive during an earthquake, causing extensive damage.

What is seismology?

Study of earthquakes and earthquake waves.

What are seismographs?

Instruments/tools used to measure and record details of earthquakes (seismicity).

What is the Mercalli Intensity Scale?

A scale that measures the intensity of earthquakes by considering its effects on the people, objects, and buildings.

What is magnitude?

The amount of energy released during an earthquake.

What is liquefaction?

When waves cause water-filled sediment to become liquefied.

When earthquake waves liquefy water-filled sediment, causing it to flow as a slurry.

What is a tsunami?

a long high sea wave caused by an earthquake, submarine landslide, or other disturbance.

What are wind waves?

Waves that break in shallow water and expend all stored energy.

What does long-term refer to in the context of earthquakes?

The probability of a certain magnitude earthquake occurring on a timescale of a certain amount of time, preferably a large amount of time.

What causes earthquakes?

Earthquakes are caused by a rapid release of energy due to tectonic stresses that cause rocks to break.

How does energy move during an earthquake?

Energy moves outwards as an expanding sphere of waves.

What are some causes of seismicity (earthquake activity)?

Motion along a crustal fracture (fault), sudden change in mineral structure, inflation of a magma chamber, volcanic eruption, landslide, meteorite impact, nuclear detonation.

What is the hypocenter (or focus) of an earthquake?

The spot within the Earth where earthquake waves originate, usually occurring on a fault surface.

What is the epicenter of an earthquake?

The land surface above the hypocenter.

Where do most earthquakes occur?

Most earthquakes occur along faults.

What is displacement?

The amount of movement along a fault.

What are faults?

Planar breaks in blocks of crust.

What are the two classifications of crustal blocks on a sloping fault?

Footwall (block below the fault) and hanging wall (block above the fault).

What is a normal fault?

A fault where the hanging wall moves down relative to the footwall, resulting from extension (stretching).

What is a reverse fault?

A fault where the hanging wall moves up relative to the footwall, resulting from compression (squeezing or shortening).

What is a strike-slip fault?

Blocks slide laterally past one another, no vertical block motion, fault surface is nearly vertical

What is fault initiation?

Tectonic forces add stress to unbroken rocks, the rock deforms slightly (elastic strain), continued stress will cause growth of cracks, eventually cracks grow to the point of failure, when a rock breaks, elastic strain transforms into brittle deformation, releasing earthquake energy

How do faults move?

Faults move in jumps, once movement starts, it quickly stops due to friction, eventually strain builds up again causing failure, termed 'stick-slip' behavior

What are seismic waves?

Body waves: pass through the Earth's interior, compressional or primary (P) waves: push-pull (compress-expand) motion, travel through solids, liquids, and gases, fastest of the seismic waves, shear or secondary (S) waves: 'shaking' motion, travel through solids, not liquids, slower than P waves, surface waves: travel along the Earth's surface, Love (L) waves: S waves that intersect the surface, move back and forth like a writhing snake, Rayleigh waves: P waves that intersect the surface, move like ripples on a pond

How does a seismograph work?

Waves always arrive in sequence, P waves first, S waves second, surface waves after that; third, the seismograph captures wave arrival

How is the epicenter of an earthquake located?

P & S waves travel at different velocities, first arrival of each depends on distance from source

What does a travel-time graph plot?

Distance from each station to the epicenter

How many stations are needed to pinpoint the epicenter?

3 or more stations

What is the radius of the circles drawn around each station?

Equal to the distance to the epicenter

What happens when circles around 3 or more stations intersect?

The point of intersection is the epicenter

How is earthquake size described?

By intensity or magnitude

How is damage described on the Mercalli Intensity Scale?

Using Roman numerals assigned to different levels of damage

Where does damage occur in relation to an earthquake?

In zones

How does damage intensity change with distance from the epicenter?

It diminishes

What does magnitude measure?

The amount of energy released

What is the maximum seismograph motion used to measure?

Magnitude

How are magnitude scales normalized?

For distance from the epicenter

What are some examples of magnitude scales?

Richter, Moment

How are magnitude scales measured?

Logarithmically

What does an increase of 1 unit on a magnitude scale represent?

A 10-fold increase in magnitude

How can earthquake energy release be calculated?

By determining the magnitude

What is the energy equivalent of a magnitude 6 earthquake?

The energy of the Hiroshima bomb

Are small or large earthquakes more frequent?

Small earthquakes

How many magnitude 3 earthquakes occur per year?

Approximately 100,000

Are large earthquakes common or rare?

Rare

How many magnitude 7 earthquakes occur per year?

Approximately 32

What are earthquakes linked to?

Plate tectonic boundaries

What types of earthquakes occur at shallow plate boundaries?

Divergent and transform boundaries

Where do intermediate and deep earthquakes occur?

Convergent boundaries

Which type of plate boundary is associated with frequent earthquakes near subduction zones?

Convergent boundaries

What are most earthquakes in continental crust associated with?

Continental transform faults, continental rifts, collision zones, or intraplate settings

What is the San Andreas Fault?

A very active strike-slip fault where the Pacific Plate meets the North American Plate

How often does the San Andreas Fault experience earthquakes?

Hundreds of earthquakes a year

What major event occurred in San Francisco in 1906?

San Francisco was destroyed by an earthquake

What percentage of earthquakes are not near plate boundaries?

5%

What are intraplate earthquakes?

Earthquakes that occur within the interior of a tectonic plate

Are intraplate earthquakes well understood?

No, they are not well understood

What are some possible causes of intraplate earthquakes?

Remnant crustal weaknesses, failed rifts, or shear zones

What is stress transmitted abroad?

The transfer of stress from one region to another.

What are isostatic adjustments?

Vertical movements of the Earth's crust in response to changes in surface loads.

What are clusters?

Groups of earthquakes that occur closely together in time and space.

What is earthquake damage?

The destruction caused by an earthquake.

What is ground shaking and displacement?

The movement and shaking of the ground during an earthquake.

How do earthquake waves arrive?

In a distinct sequence.

What causes different motion during an earthquake?

Different waves.

What are P waves?

The first waves to arrive during an earthquake, producing rapid up and down motion. They can also move through solids, liquids, and gases

What are S waves?

The second waves to arrive during an earthquake, producing back and forth motion. They can only move through solids

What is the severity of shaking and damage dependent on?

Magnitude, distance from hypocenter, intensity and duration of vibrations, and the nature of the subsurface material.

What happens during landslides and avalanches?

Slopes fail and rockslides and avalanches occur following earthquakes in uplands.

What happens during tsunamis?

The sea floor changes due to an earthquake, displacing water and creating waves that race rapidly away.

How are tsunamis different from wind waves?

Tsunamis are caused by earthquakes and have a larger scale and greater destructive potential compared to wind waves.

What is the wavelength of tsunamis?

The wavelength of tsunamis is measured in kilometers.

How are wave height and speed of tsunamis different from wind?

Wave height and speed of tsunamis are not determined by wind.

What is the speed of tsunamis?

The speed of tsunamis can reach hundreds of kilometers per hour.

How do tsunamis come ashore?

Tsunamis come ashore as a raised plateau of water that pours onto land.

What were the impacts of the Indian Ocean Tsunami in 2004?

The Indian Ocean Tsunami in 2004 destroyed coastlines around the Indian Ocean and caused complete devastation below the 'run-up' elevation.

Which area was hardest hit by the Indian Ocean Tsunami in 2004?

Banda Aceh, with its dense coastal development, was the hardest hit by the Indian Ocean Tsunami in 2004.

What happened to entire communities during the Indian Ocean Tsunami in 2004?

Entire communities were erased by the Indian Ocean Tsunami in 2004.

What can Earthquake prediction help do?

Earthquake prediction can help reduce catastrophic losses.

Can earthquakes be predicted?

Yes and no. Earthquakes can be predicted in the long term, but not for the short term.

What is the purpose of mapping seismic hazards?

Mapping seismic hazards helps assess risk and is useful for developing building codes, land-use planning, and disaster planning.

What does long-term earthquake prediction involve?

Long-term earthquake prediction involves estimating the probability of a certain magnitude earthquake occurring on a timescale of 30-100 years or more.

What is the premise of long-term earthquake prediction?

Long-term earthquake prediction is based on the premise that earthquakes are repetitive.

What are the types of faults?

normal, reverse, thrust, strike-slip, oblique-slip, stick-slip

What is the Richter scale?

A scale that rates an earthquake's magnitude based on the size of its seismic waves.

Where do you send FEMA after an earthquake?

the epicenter

3 MULTIPLE CHOICE OPTIONS

True or False: In a thrust fault, the headwall moves down relative to the footwall.

False

1 MULTIPLE CHOICE OPTION

Which of the following are body waves?

P waves and S waves

Which scale describes the amount of energy released during an earthquake?

Richter Scale

3 MULTIPLE CHOICE OPTIONS