Earth Science Chapter 8 Definitions Flashcards

Earthquake Concepts

• Earthquake: A vibration of Earth from the rapid release of energy.
• Focus: The origin point of an earthquake beneath the Earth's surface.
• Faults: Fractures in Earth where movement has occurred.

Seismic Mechanics

• Elastic Rebound: Rocks deform and, upon breaking, release stored energy leading to an earthquake’s vibrations.
• Aftershock: A smaller earthquake that occurs following the main earthquake event.
• Foreshock: A smaller earthquake that typically occurs before a more significant earthquake.

Seismology and Measurement

• Seismology: The scientific study of earthquakes and seismic waves.
• Seismograph: An instrument used to record the vibrations produced by seismic waves.
• Seismogram: The output or the record generated by a seismograph.

Types of Seismic Waves

• Surface Waves: Seismic waves that travel along Earth’s surface, often causing the most damage.
• Body Waves: Seismic waves that move through the Earth's interior.
• Primary (P) Waves: Compression waves that push and pull rocks in line with their direction.
• Secondary (S) Waves: Waves that cause particles to shake perpendicular to their direction of travel.

Earthquake Location and Impact

• Epicenter: The surface point directly above the earthquake's focus.
• Circum-Pacific Belt: The major zone where most earthquakes occur globally.
• Intensity: A measure of shaking at a specific location based on damage.
• Magnitude: The total energy released during an earthquake.

Measurement Scales

• Modified Mercalli Intensity Scale: Rates shaking and damage variances across locations.
• Richter Scale: A logarithmic scale from 1 to 10 used to quantify earthquake energy release.
• Moment Magnitude Scale: A more precise measure based on fault displacement and energy estimation.

Geological Effects

• Liquefaction: A phenomenon where shaking causes wet soil to act like a liquid.
• Seismic Sea Waves (Tsunami): Water waves generated by seismic events, volcanic activity, or landslides.

Earth Layers

• Crust: The thin outer layer of Earth.
• Mantle: The rocky layer beneath the crust, approximately 2900 kilometers thick.
• Lithosphere: The cool and rigid layer that includes the crust and uppermost mantle.
• Asthenosphere: The soft layer under the lithosphere where lithospheric plates move.

Core Structure

• Lower Mantle (Mesosphere): Rigid and brittle layer constituting 80% of Earth’s material, located between 670-2900 km depth.
• Core: The central part of Earth made up of iron and nickel.
• Outer Core: A liquid layer within the core, characterized by mobile properties.
• Inner Core: A solid metallic sphere made primarily of nickel and iron.

Geophysical Boundaries

• Moho: The boundary separating the crust from the mantle.
• Refracted Waves: Waves in shallow water that slow down, bend, and align with underwater contours.
• Shadow Zone: An area between 105 and 140 degrees from an earthquake epicenter where direct P waves are absent due to refraction through the Earth's core.