Understanding Earthquakes and Faults

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Questions and Answers

What is the primary reason that fault motion is stopped?

Irregularities on the fault surface (correct)

Excessive heat in the Earth's crust

The surrounding rock is too weak

Increased pressure on the fault

What term describes the behavior where friction prevents motion followed by a sudden slip?

Motion-resist behavior

Slip-stick behavior

Stick-slip behavior (correct)

Friction-slip behavior

Which type of seismic wave travels through the Earth's interior?

Love waves

Rayleigh waves

P-waves (correct)

Surface waves

Why do larger earthquakes tend to have larger areas of slip?

They release more accumulated stress Signup and view all the answers

What typically follows a major earthquake and indicates ongoing movement in the crust?

Aftershocks Signup and view all the answers

Which wave is characterized as the slowest and most destructive among seismic waves?

L-waves Signup and view all the answers

How does a fault slip change with distance from the hypocenter?

Displacement diminishes Signup and view all the answers

P-waves are distinguished from S-waves by which characteristic?

P-waves travel faster than S-waves Signup and view all the answers

What type of motion do S-waves produce as they travel through materials?

Back and forth motion Signup and view all the answers

Which type of wave is the fastest?

P-waves Signup and view all the answers

What is a seismometer primarily used for?

To measure ground motion Signup and view all the answers

Which wave is described as causing the ground to ripple like water?

R-waves Signup and view all the answers

What is the significance of the time separation between P-wave and S-wave arrivals?

It helps determine the distance to the epicenter Signup and view all the answers

Which type of seismic waves can travel through liquids?

P-waves Signup and view all the answers

How are the epicenter and distance from a seismic station determined?

By triangulating distances from three or more stations Signup and view all the answers

Which type of waves are the most destructive during an earthquake?

R-waves Signup and view all the answers

What measurement describes the severity of damage during an earthquake?

Mercalli Scale Signup and view all the answers

How is the intensity of earthquake damage designated on the Mercalli Scale?

Using Roman numerals Signup and view all the answers

What is the energy released during a magnitude 6.0 earthquake comparable to?

Hiroshima atomic bomb Signup and view all the answers

How many times greater is a magnitude 8.0 earthquake compared to a magnitude 4.0 earthquake?

At which type of plate boundary do most shallow earthquakes predominantly occur?

Divergent and transform boundaries Signup and view all the answers

Which magnitude scale is most accurate for measuring earthquake size?

Moment Magnitude Scale Signup and view all the answers

What type of faulting is associated with divergent plate boundaries?

Normal faulting Signup and view all the answers

What characterizes the ground motion measurement of an earthquake's magnitude?

It is a uniform logarithmic measurement Signup and view all the answers

What is the most common cause of earthquakes?

Sudden slip along a fault Signup and view all the answers

Where does the hypocenter of an earthquake occur?

On the fault surface where slip occurs Signup and view all the answers

Which of the following statements about faults is true?

Active faults show motion due to ongoing stresses Signup and view all the answers

What is meant by 'fault scarp'?

The visible part of the fault at the surface Signup and view all the answers

What happens to rocks under continued tectonic stress?

They crack eventually leading to a fault Signup and view all the answers

Which force resists motion along a fault?

Friction Signup and view all the answers

How often do detectable earthquakes occur on Earth?

Over a million times per year Signup and view all the answers

What occurs at the epicenter of an earthquake?

It is the location on the land surface above the hypocenter Signup and view all the answers

Study Notes

What Causes Earthquakes?

Earthquakes are caused by the rapid release of energy, often from tectonic plate movement.
Earthquakes occur daily, with over a million detectable events annually.
Other causes of earthquakes include:
- Sudden slip along a new or existing fault.
- Movement of magma in a volcano.
- Giant landslides.
- Nuclear detonations.

Components of Earthquakes

The hypocenter (focus) is where fault slip occurs, typically on a fault surface.
Earthquake waves expand outward from the hypocenter.
The epicenter is the point on the Earth's surface directly above the hypocenter.

Faults in the Crust

Faults are breaks or fractures in the Earth's crust.
Active faults are those where ongoing stress produces motion.
Inactive faults experienced motion in the geological past.
A fault trace represents the intersection of a fault with the ground surface.
Displacement at the surface creates a fault scarp.
Some faults, known as blind faults, do not extend to the surface.

Generating Earthquake Energy

Tectonic forces apply stress (push, pull, or shear) to rocks.
Rocks bend slightly without breaking due to their elastic properties.
Continued stress leads to crack development and growth within rocks.
Eventually, cracking leads to failure (faults = brittle deformation), releasing stored elastic energy at once.
Stick-slip behavior describes the cyclical process of fault movement:
- Stick phase: friction prevents motion.
- Slip phase: Friction is briefly overcome by motion.

Seismic Waves

Seismic waves are energy waves emanating from the focus of an earthquake.
Body waves travel through Earth's interior:
- P-waves (primary or compressional waves):
  - Travel by compressing and expanding material.
  - Material moves back and forth parallel to wave direction.
  - Fastest seismic waves, traveling through solids, liquids, and gases.
- S-waves (secondary or shear waves):
  - Travel by moving material back and forth.
  - Material moves perpendicular to wave travel direction.
  - Slower than P-waves, traveling only through solids.
Surface waves travel along Earth's exterior:
- L-waves (Love waves):
  - S-waves intersecting the land surface.
  - Move the ground back and forth like a snake.
  - Slowest, but most destructive, surface waves.
- R-waves (Rayleigh waves):
  - P-waves intersecting the land surface.
  - Cause the ground to ripple up and down like water.

How Do We Measure Earthquakes?

Seismometer: instrument that records ground motion.
A weighted pen on a spring traces the movement of the frame.
- Vertical motion: Records up-and-down movement.
- Horizontal motion: Records back-and-forth movement.
Seismogram: Data recording earthquake wave behavior.
- Earthquake waves arrive at a station in a specific order:
  - P-waves first.
  - S-waves second.
  - Surface waves last.
- Arrival times determine the distance to the epicenter.

Finding the Epicenter

P-waves consistently arrive before S-waves.
The time separation between P-wave and S-wave arrivals increases with distance from the epicenter.
Triangulation: Data from three or more seismic stations pinpoints the epicenter by intersecting circles.

Earthquake Size

Earthquake size is described using two measurements:
Intensity (Mercalli Scale):
- Measures the severity of damage.
- Damage is assigned Roman numerals (I = low, XII = high).
- Damage occurs in zones and diminishes with distance.
Magnitude (Moment Magnitude Scale):
- Most accurate measure of earthquake size.
- Measures the maximum amplitude of ground motion.
- Magnitude scales are logarithmic:
  - M6.0 is 10 times larger than M5.0.
  - M6.0 is 100 times larger than M4.0.
  - M8.0 is 10,000 times larger than M4.0.

Earthquake Occurrence

Earthquakes are concentrated along plate tectonic boundaries.
Divergent boundaries:
- Shallow earthquakes (mid-ocean ridges).
Transform boundaries:
- Shallow earthquakes.
Convergent boundaries:
- Shallow, intermediate, and deep earthquakes.

Earthquakes at Plate Boundaries

Divergent plate boundaries (mid-ocean ridges):
- Two types of faulting occur.

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Description

This quiz explores the causes and components of earthquakes, including the role of faults in the Earth's crust. Test your knowledge on how tectonic movements, volcanic activity, and other factors contribute to seismic events, as well as key terminology like hypocenter and epicenter.