Exam 2 Study Guide: Earthquakes, Tsunamis, and Volcanic Activity

Vocabulary flashcards covering core geological terminology, natural hazard classifications, and mechanics for earthquakes, tsunamis, and volcanic activity from Chapters 6 through 8.

Stress

Force exerted per unit area within rock or other Earth material.

Strain

Deformation in a rock's size, shape, or orientation caused by stress.

Rock strength

How much stress rock can withstand before it fails.

Earthquake

Sudden release of stored energy caused by rock failure and movement, commonly along a fault.

Focus (hypocenter)

Point below Earth's surface where rupture begins.

Epicenter

Point on Earth's surface directly above the focus.

Fault

Fracture in rock along which movement occurs.

Seismograph / seismometer

Instrument that detects and records seismic waves.

Seismogram

The record produced by a seismograph.

Paleoseismology

Study of prehistoric earthquakes using evidence preserved in the geologic record.

Magnitude

Measure of earthquake size and energy released at the source.

Intensity

Description of observed shaking and damage at a particular location.

Moment magnitude ($M_w$)

A magnitude scale widely applicable across a broad range of earthquake sizes.

Richter magnitude

A magnitude scale based on seismic-wave amplitude that is less useful across the full range of very large events.

Modified Mercalli Intensity (MMI)

A $12$-level qualitative scale based on observed shaking and damage at a particular location.

Intraplate earthquake

An earthquake that occurs within a plate, away from its boundaries.

P wave (primary)

Compressional / push-pull seismic wave; fastest; travels through solids, liquids, and gases, arriving first.

S wave (secondary)

Shear motion seismic wave; slower than P waves; travels through solids but not liquids.

Surface waves

Seismic waves that travel along Earth's surface; generally slowest and often cause the most damage at the surface.

Material amplification

A phenomenon where ground shaking is stronger in loose, unconsolidated sediment than in dense, solid rock because seismic waves behave differently in different materials.

Ground acceleration

A measurement of how rapidly ground velocity changes, often expressed relative to gravitational acceleration ($g$).

Supershear rupture

Rupture that propagates faster than the relevant seismic shear-wave speed, creating strong shock-like ground motion, especially in some long strike-slip ruptures.

Elastic-rebound concept

Concept describing rocks deforming as stress builds and then suddenly slipping/rebounding when a fault ruptures.

Seismic gap

A section of a fault that has not ruptured recently compared with nearby sections.

Earthquake early-warning systems

Systems that detect the first arriving waves and send alerts before stronger shaking arrives.

Tsunami

Japanese term meaning 'large harbor waves'; a series of waves produced by sudden displacement of ocean or lake water.

Local tsunami

A tsunami that travels toward a nearby coast and can arrive very quickly after the triggering event, leaving little time for official warnings.

Distant tsunami

A tsunami that crosses the deep ocean for thousands of kilometers and may strike remote coasts.

Tsunami runup maps

Maps that show how far inland water has traveled or could travel and help identify areas likely to be inundated.

Tsunami watch

An advisory issued when a potentially tsunami-generating earthquake has occurred and a tsunami may be possible.

Tsunami warning

An alert issued when a tsunami has been detected or is expected to affect the area, requiring immediate protective action.

Viscosity

A liquid's resistance to flow.

Shield volcano

A volcano with a broad shape and gentle slopes built mainly from repeated basaltic lava flows.

Composite volcano / stratovolcano

A steep, cone-shaped volcano with intermediate-silica magma that alternates explosive activity and lava flows.

Volcanic dome

A feature formed from very viscous, often silica-rich lava that piles up near the vent; rhyolite is a common rock type.

Cinder cone

A relatively small volcano built from tephra, including volcanic ash and larger fragments such as bombs.

Caldera

A large collapse depression, typically associated with major eruptions and collapse after magma withdrawal.

Fissure eruption

An eruption where lava emerges through a long crack rather than a single central vent, potentially producing extensive basaltic flows.

Pahoehoe lava

Lava with a relatively smooth, ropy surface that is typically hotter and less viscous.

Aa lava

Lava with a rough, blocky surface that is typically more viscous and cooler than pahoehoe.

Pyroclastic flow

Fast-moving, extremely hot mixture of gas, ash, and rock fragments; among the deadliest volcanic hazards.

Ash fall

Fine volcanic fragments carried through the air and deposited over broad areas.

Lahar

A rapid, fast-moving flow of water mixed with volcanic debris down valleys and river channels.

Vog

Volcanic smog produced by volcanic gases that can contribute to acid rain and contamination.