GEOL 200: Earth’s Fury – Midterm #2 Review Sheet

A comprehensive set of flashcards based on the lecture notes for the GEOL 200 course, covering key concepts about faults, earthquakes, seismic waves, and tsunami.

What is the definition of a fault?

A fracture or zone of fractures between two blocks of rock.

What is a fault scarp?

A steep slope or cliff formed by vertical displacement on a fault.

What is stress in geology?

The force applied per unit area on a material.

What are the two main types of stress?

Tensile stress and compressive stress.

What is strain?

The deformation resulting from stress.

What is ductile deformation?

The ability of a material to deform plastically without fracturing.

What is brittle deformation?

When a material breaks or fractures under stress.

How does the mode of deformation vary with depth?

Deformation tends to be ductile at greater depths and brittle at shallower depths.

What are strike and dip of a planar fault?

Strike is the direction of the line formed by the intersection of a fault plane and a horizontal surface; dip is the angle of the fault plane relative to the horizontal.

What is the difference between strike-slip and dip-slip faults?

Strike-slip faults involve horizontal movement, while dip-slip faults involve vertical movement.

What are the two types of strike-slip faults?

Right-lateral and left-lateral faults.

What are the two types of dip-slip faults?

Normal faults and reverse (thrust) faults.

What is the hanging wall?

The block of rock that lies above the fault plane.

What is the foot wall?

The block of rock that lies below the fault plane.

What is a blind thrust fault?

A fault that does not have a surface expression and can be dangerous due to its hidden nature.

Name an example of a deadly earthquake on a blind thrust fault.

The Northridge earthquake in 1994

How do faults manifest in surface topography?

Faults can create features such as scarps, offset rivers, and changes in elevation.

Which types of faults are found at divergent, convergent, and transform boundaries?

Divergent boundaries have normal faults, convergent boundaries have reverse faults, and transform boundaries have strike-slip faults.

What kinds of faults created the Basin and Range?

Normal faults

What is a megathrust earthquake?

A large subduction zone earthquake.

What happens to the overriding and subducting plates during a megathrust earthquake?

The subducting plate is forced downward while the overriding plate is uplifted.

Name two famous strike slip faults.

The San Andreas Fault and the North Anatolian Fault.

Are they right- or left-lateral?

The San Andreas Fault is right-lateral, and the North Anatolian Fault is left-lateral.

What are the ways that earthquakes can affect the chances of quakes occurring on other faults?

Earthquakes can change stress on adjacent faults, potentially triggering more quakes.

What is illustrated by the progression of seismicity on the North Anatolian Fault?

It illustrates the concept of seismic waves propagating and stress transfer.

What is elastic rebound?

The process where deformed rocks return to their original shape after an earthquake.

What is the pattern of displacement across a fault in a strike slip earthquake?

it is horizontal in strike-slip earthquakes.

How about between earthquakes?

Between earthquakes, stress builds up gradually.

How do we measure displacements that result from earthquakes?

By using GPS and surveying techniques.

What is the characteristic earthquake model?

It is a model that predicts the timing and magnitude of earthquakes based on previous activity.

How do stress and displacement vary with time in the characteristic earthquake model?

Stress increases over time until it is released during an earthquake.

How would you use the characteristic earthquake model to predict earthquake occurrence rate?

You would estimate the recurrence interval based on slip rate and past events.

What does the characteristic earthquake model predict for the timing of the 1906 San Francisco and 1857 Fort Tejon quakes?

These quakes are expected to repeat every 150 years.

What is the Parkfield experiment?

An experiment to observe and predict earthquakes on the San Andreas Fault.

Were precursors observed at Parkfield?

Yes, some precursors were observed.

Was the Parkfield prediction successful?

No, the prediction was not entirely successful.

What is the meaning of the term 'recurrence interval'?

The average time between successive earthquakes at a given location.

What is a time-predictable earthquake model?

It assumes earthquakes occur after a certain time interval based on stress accumulation.

How do stress and displacement vary with time in the time-predictable model?

Stress increases consistently over time until a rupture occurs.

What is a slip-predictable earthquake model?

It assumes earthquake recurrence depends on the amount of slip on the fault.

How do stress and displacement vary with time in the slip-predictable model?

Stress can build up, but displacement determines when an earthquake will occur.

How does variable loading affect the evolution of stress and displacement with time?

It can cause changes in how stress accumulates and is released.

What are seismic gaps?

Segments of a fault that have not experienced recent earthquakes.

What might seismic gaps tell us about a fault?

They may indicate areas where stress is building and earthquakes may occur.

Was the Tohoku earthquake predicted?

No, the Tohoku earthquake was not predicted.

What was surprising about the Tohoku earthquake?

The magnitude and the extent of damage caused were surprising.

What are amplitude, wavelength, period, and frequency of a wave?

Amplitude is height, wavelength is distance between waves, period is time between waves, frequency is the number of waves per unit time.

Is matter, energy, or both carried by a seismic wave?

Seismic waves carry energy.

What are seismic body waves?

Seismic waves that travel through the Earth's interior.

What are seismic surface waves?

Seismic waves that travel along the Earth's surface.

What are the two types of body waves?

P-waves (primary waves) and S-waves (secondary waves).

How fast do body waves travel?

Both high speeds with P-waves (6-8km/s) travelling faster than S-waves(3-5km/s).

What kind of particle motions do body waves have?

P-waves have compressional particle motion, while S-waves have shear particle motion.

What are the two types of surface waves?

Love waves and Rayleigh waves.

How fast do surface waves travel?

Surface waves travel slower than body waves. (2-5km/s)

What kind of particle motions do surface waves have?

Love waves involve horizontal motion, while Rayleigh waves involve elliptical motion.

Which waves are least destructive?

P-waves are least destructive.

Which waves are most destructive close to an earthquake?

Surface waves are most destructive close to an earthquake.

And far away from earthquakes?

Still surface waves since they lose energy slower. Body waves are less destructive but still measure the earthquake's nature.

What is a seismometer?

An instrument that detects and measures ground motion.

What is a seismograph?

An instrument that records the motion of a seismic wave.

What is a seismogram?

The output record produced by a seismograph.

On what principle do seismometers function?

Seismometers function based on inertia and the relative motion between a mass and the ground.

What is the seismoscope?

An ancient device that detects earthquakes.

What was its limitation?

It could only provide a simple indication of earthquake occurrence.

What is EarthScope USArray?

A program designed to study the structure and dynamics of the North American continent.

What can GPS and InSAR be used for?

They are used to characterize an earthquake cycle and measure co-seismic displacement.

What can seismometers detect?

Seismic waves produced by earthquakes or explosions.

What is an earthquake hypocenter?

The point within the earth where an earthquake starts.

What is the focus?

The exact location where the earthquake rupture begins.

What is the epicenter?

The point on the earth's surface directly above the hypocenter.

How do we locate earthquakes using P and S travel times?

By measuring the difference in travel times between P-waves and S-waves.

What is the earthquake (seismic) moment?

It's a measure of the size of an earthquake based on the area of the fault slip.

How is seismic moment calculated?

It is calculated by multiplying the area of the fault that slipped by the average slip.

What are the body wave (mb), surface wave (MS), and local magnitudes (ML)?

These are scales used to measure the magnitude of earthquakes.

What is the Richter magnitude?

A logarithmic scale used to measure the size of earthquakes based on seismic waves.

Which geographic region is the Richter magnitude designed for?

It was primarily designed for local earthquakes in Southern California.

What is magnitude saturation, and why does it happen?

When magnitude estimates become inaccurate for very large events.

How does it affect mb(body waves) and MS(surface waves) vs. MW (moment magnitude)?

It causes discrepancies between local and moment magnitudes.

What is the moment magnitude (MW)?

A more accurate measure of an earthquake's size based on seismic moment.

What physical quantity is it related to?

It is related to the total amount of energy released during an earthquake.

How much does earthquake energy increase with each increment of moment magnitude?

Energy increases by a factor of approximately 32 for each whole number increase in magnitude.

How much more energy does a Mw = 6 quake release compared to a Mw = 5 one?

A Mw = 6 quake releases approximately 32 times more energy than a Mw = 5 quake.

How do rupture length and average displacement (slip on a fault) vary with increasing moment?

Both rupture length and average displacement increase with greater moment magnitude.

What is the Gutenberg-Richter relation?

It describes the relationship between the frequency and magnitude of earthquakes.

What is typically the slope of the best-fit line to the frequency-magnitude plot?

The slope is typically about -1.

How does the frequency of occurrence of earthquakes depend on magnitude?

Larger magnitude earthquakes occur less frequently than smaller ones.

Why does the observed number of quakes always fall below the Gutenberg-Richter prediction?

Because some earthquakes are too small to be detected.

What is this critical magnitude called?

The detection threshold.

Why does the observed number of quakes deviate from the Gutenberg-Richter prediction for very large earthquakes?

Due to the complexity and variability of fault behavior.

What fraction of total energy released by earthquakes is released by the largest events?

around 75-90%

What is the relationship between rupture length and average displacement on a fault?

Generally, longer ruptures correspond to greater average displacements.

What is the relationship between rupture length and earthquake magnitude?

Larger magnitude earthquakes tend to have longer ruptures.

How much slip do you expect in an Mw = 7 quake?

1-7 meters

How much slip do you expect in an Mw = 6 quake?

Estimated slip can be about 1 meter.

How long is the rupture expected for an Mw = 7 quake?

tens to hundreds of kilometers

How long is the rupture expected for an Mw = 6 quake?

6-20km

Why do aftershocks occur?

Aftershocks occur due to the readjustment of the fault after the main shock.

What is Omori’s Law?

It describes the decay rate of aftershocks over time.

What does Omori’s Law tell us?

Aftershocks decrease logarithmically in frequency over time.