Earthquakes Lecture Review

Flashcards covering key vocabulary terms related to earthquakes, including their causes, measurements, effects, and risk management strategies based on lecture notes.

Elastic Rebound Theory

Explains why earthquakes happen, involving cold, brittle, and elastic rocks that bend under stress until stress exceeds strength, causing them to break and release stored energy as seismic waves.

Fault Rupture

The crack in the ground along which rocks slide during an earthquake.

Earthquake Cycle

A process involving a long period of stress accumulation and elastic deformation, followed by stress/energy release when the fault slips, and then the process repeats.

Earthquakes at Divergent Plate Boundaries

Typically weak and shallow earthquakes because rocks are weak when subjected to tension, breaking before large elastic deformation can occur, and becoming plastic below about 15 km depth.

Earthquakes at Transform Plate Boundaries

Can range from weak to strong because rocks are strong when subjected to shear stress, occurring at depths less than 20 km.

Earthquakes at Convergent Plate Boundaries (Subduction Zones)

Can range from weak to very strong, with depths ranging from shallow to deep, due to rocks being very strong when subjected to compression.

Seismometer

A device used to study seismic waves, measuring ground motion either with a pen on a rotating drum or using digital accelerometers.

P-waves

Primary, fastest seismic waves that cause a tiny amount of ground motion, moving material back and forth in the direction of travel as compression waves.

S-waves

Secondary seismic waves that have more motion than P-waves and medium speed, moving material up and down perpendicular to the direction of travel as shear waves.

Surface Waves

Slowest seismic waves that create the most ground motion, causing material to move in all three directions, including some rotational motion.

Locating the Epicenter

Determined by using the time gap between P and S wave arrivals at multiple seismic stations (at least three) to triangulate the earthquake's origin.

Earthquake Intensity

Refers to the degree of ground shaking and the impacts experienced at a particular location.

Earthquake Magnitude

Can refer to the amplitude of ground shaking or the energy released by the earthquake.

Modified Mercalli Intensity Scale

A semi-quantitative scale used to describe the intensity of historical earthquakes, particularly those before seismometers were developed.

Richter Magnitude (M)

Measures the maximum amplitude of ground shaking on a logarithmic scale, where an M7 is ten times as much shaking as an M6.

Moment Magnitude (Mw)

Measures the amount of energy released during a quake on a logarithmic scale, where a 7 is much more powerful than a 6.

Earthquake Prediction

Currently impossible to achieve, with scientists only able to estimate approximate earthquake frequency based on historical activity.

Seismic Hazard

Refers to the potential for ground shaking in a given area.

Seismic Risk

Refers to the potential for damage, including lives lost and structures damaged, from an earthquake.

Liquefaction of Sediment

A seismic risk where wet clay layers or loose, saturated sediments lose strength and behave like a liquid during ground shaking, causing structures to sink or tip.

Tsunami

A seismic risk initiated by the uplift of the seafloor during an earthquake, pushing up a wide area of ocean water that creates powerful waves.

Earthquake Engineering

Designing buildings and structures to better withstand ground shaking, often demanding at least 'crawl out' survivability.

Better Land-Use Planning

A strategy to reduce seismic risk by preventing construction on fault lines or in high-susceptibility areas.

Real-Time Warning System

A system that detects fast-traveling P-waves to provide 10-100 seconds of warning before damaging S-waves and surface waves arrive, allowing for automated safety measures and evacuations.

Effective Disaster Response

A measure to reduce seismic risk involving organized efforts by government (firefighters, rescue) and citizens (emergency supplies, first aid) to manage the aftermath of an earthquake.