Earthquakes: A Concise Visual Study Guide

Comprehensive vocabulary flashcards reviewing the concepts, seismic waves, measurement scales, hazards, damage factors, monitoring techniques, and mitigation strategies of earthquakes.

Earthquake

The sudden release of energy along a fault line caused by movement in tectonic plates, which results in the shaking of the Earth's crust.

Focus

The point deep in the Earth's crust where an earthquake begins.

Epicentre

The point on the Earth's surface directly above the focus, which is often the area that experiences the most damage.

Fault Line

The break in the Earth's crust along which energy is suddenly released during an earthquake.

Seismic Waves

Tremors that spread out from the focus deep in the crust following the release of energy.

Subduction Zones

Plate boundaries where higher-magnitude earthquakes typically occur, exemplified by the Pacific Ring of Fire.

Transform Plate Boundaries

Plate boundaries where tectonic plates slide past each other, exemplified by the San Andreas Fault.

Divergent Plate Boundaries

Plate boundaries where tectonic plates pull apart from one another, exemplified by the Mid-Atlantic Ridge.

Shallow Focus Earthquakes

The most common and most dangerous earthquakes, having a focus close to the surface (less than $70\,\text{km}$) and occurring at plate boundaries when a plate sinks and becomes stuck.

Deep Focus Earthquakes

Earthquakes occurring at subduction zones at depths deeper than $300\,\text{km}$ as one plate moves beneath another; surface damage is rare because of their great depth.

Seismograph

An instrument designed to detect, measure, and record seismic waves released from earthquakes.

Primary Waves (P-waves)

The fastest seismic body waves and the first to arrive; they are capable of traveling through molten (magma) material.

Secondary Waves (S-waves)

Slower-moving body waves that are second to arrive; they travel through solid rock.

Surface Waves

The slowest of all seismic waves and the last to arrive; they cause the ground to move up and down.

Richter Scale

A scale measuring ground movement caused by earthquakes, where each point represents a $10\text{-fold}$ increase in power (with Moment Magnitude often used now).

Mercalli Scale

A $12\text{-point}$ scale ($\text{I}$ to $\text{XII}$) that measures earthquake damage, ranging from $1$ (no damage) to $\text{XII}$ (complete desolation).

Infrastructure Damage

Direct physical destruction caused by an earthquake, including structural failure of buildings and bridges, falling debris, and the need for rescue workers to search rubble.

Tsunami

A series of ocean waves generated when plate movement displaces water, creating a hump of water that collapses, spreads outward, and slows while rising near the shore before crashing into the coastline.

Liquefaction

A phenomenon where ground shaking causes solid soil to temporarily behave like a liquid, leading to soil instability, building collapses, and broken gas and sewage pipes.

Long-Term Effects (Earthquakes)

Prolonged consequences following an earthquake, including outward migration, spread of disease due to compromised water and shelter, and economic slowdown.

Focus Depth (Damage Factor)

A factor determining the severity of shaking, where shallow focus earthquakes cause significantly more surface destruction than deep focus earthquakes.

Geology (Damage Factor)

A geological condition affecting shaking severity, where loose soil and boggy ground significantly elevate the likelihood of liquefaction.

Global North vs. Global South (Damage Factor)

Socioeconomic disparity influencing earthquake impact, where the Global North possesses more money, resources, and services to prepare for and respond to disasters.

Tiltmeters

Monitoring instruments that measure bulges in the land surface to reveal changes in land levels along fault lines.

Lasers (Earthquake Monitoring)

Instruments used to monitor subtle changes and shifts in ground or rock movement along fault zones.

Seismic Gap

A period of inactivity or the time gap between earthquakes along an active fault line, during which tiltmeters record changes occurring across land levels.

Early Warning Systems (EWS)

Tools and processes used to identify, monitor, forecast, and communicate potential earthquake hazards to save lives and alert people via seismographs, as utilized in Japan.

Earthquake-Resistant Buildings

Structures engineered with strict regulations using steel frames, shock absorbers to reduce seismic shock, deep foundations to avoid liquefaction, and slightly elastic elements that sway.

Urban Planning (Earthquake Mitigation)

The deliberate design of settlements to ensure functionality, sustainability, and liveability, including positioning open spaces away from fault lines.