Earthquakes and Faults

Fault

A fault is a fracture or zone of fractures in the Earth's crust where blocks of rock have moved relative to each other.

Normal Fault

Occur in regions experiencing extensional forces. The hanging wall block moves downward relative to the footwall block.

Reverse Fault

Occur in regions experiencing compressional forces. The hanging wall moves upward relative to the footwall.

Thrust Fault

A type of reverse fault that has a low-angle dip compared to regular reverse faults.

Strike-Slip Fault

Occur when two blocks of rock slide past each other horizontally.

Left-lateral Fault

A type of strike-slip fault where the opposite block moves to the left.

Right-lateral Fault

A type of strike-slip fault where the opposite block moves to the right.

Tension

Forces that pull rocks apart, leading to normal faults.

Compression

Forces that push rocks together, leading to reverse faults.

Shear

Forces that cause sliding along a fault, leading to strike-slip faults.

Earthquake

An earthquake is the shaking of the Earth's surface caused by the sudden release of energy in the Earth's lithosphere, creating seismic waves.

P-Waves

Longitudinal waves that compress and expand the material they travel through, traveling at about 6 km/s in the Earth.

S-Waves

Transverse waves that move material up and down or side to side, traveling at about 3.5 km/s.

Surface Waves

Waves that travel along the Earth's surface and cause most of the destruction during an earthquake.

Love Waves

A type of surface wave that moves horizontally, causing horizontal shaking.

Rayleigh Waves

A type of surface wave that moves in a rolling motion, causing both vertical and horizontal movement.

Magnitude

Measures the energy released at the source of the earthquake (e.g., Richter scale, Moment Magnitude scale).

Intensity

Measures the effects of an earthquake at specific locations (e.g., Modified Mercalli Intensity scale).

Triangulation

A method used to determine the location of an earthquake's epicenter by analyzing the arrival times of seismic waves at multiple seismic stations.

Data Collection

Seismic stations record the arrival times of P-waves and S-waves.

Calculate Distances

The time difference between the arrival of P-waves and S-waves is used to calculate the distance from each station to the epicenter.

Draw Circles

Each distance is represented as a circle around the station.

Intersection Point

The epicenter is located at the point where all circles intersect.

Example Calculation

If a station records the arrival of a P-wave at 2 seconds and an S-wave at 5 seconds, the difference (3 seconds) helps calculate the distance based on known wave speeds.

Intensity Scales

Intensity scales measure the effects and damage caused by an earthquake at specific locations, rather than measuring the energy released.

Modified Mercalli Intensity Scale (MMI)

Scale: Ranges from I (not felt) to XII (total destruction). Basis: Based on observations, reports from people, and damage assessments.

Mercalli Scale

Similar to MMI: Measures effects but less commonly used in modern research.

Importance of Intensity Scales

Intensity scales help in assessing the impact of earthquakes on structures and populations.

Shadow Zones

Areas on the Earth's surface where seismic waves are not detected after an earthquake, indicating different materials in the Earth's interior.

P-Wave Shadow Zone

Cause: P-waves are refracted by the liquid outer core, creating a zone where they cannot be detected. Location: Typically found between 104° and 140° from the earthquake's epicenter.

S-Wave Shadow Zone

Cause: S-waves cannot travel through liquids, so there is a larger shadow zone indicating the presence of the liquid outer core. Location: Generally extends from the epicenter to about 104°.

Significance of Shadow Zones

Shadow zones provide crucial information about the Earth's internal structure and composition.

Key Concepts to Remember

Understand the different types of faults and the forces that cause them.

Seismic Wave Types

Familiarize yourself with seismic wave types and their characteristics.

Practice Triangulation

Practice triangulation methods for locating an earthquake epicenter.

Learn Intensity Scales

Learn how intensity scales measure the effects of earthquakes.

Recognize Shadow Zones

Recognize the significance of shadow zones in understanding Earth's interior.

Study Tips

Use diagrams to visualize fault types and wave movements.

Create Flashcards

Create flashcards for key terms and definitions.

Practice Calculating Distances

Practice calculating distances using triangulation with example problems.

Discuss Real-World Examples

Discuss real-world examples of earthquakes to understand impacts and recovery.