Key Concepts in Seismology and Earthquake Dynamics

Tectonic Boundaries

Most earthquakes occur along plate boundaries, particularly at convergent (subduction zones), transform, and divergent boundaries.

Ring of Fire

The Pacific Ring of Fire has the highest earthquake activity, especially around Japan, Indonesia, Chile, and the west coast of North America.

Intraplate Earthquakes

Less common but still significant, occurring within a tectonic plate rather than at the edges (e.g., the New Madrid Seismic Zone in the central U.S.).

Subduction Zones

The largest earthquakes (magnitude 8-9+) occur at megathrust faults where one plate is forced under another (e.g., Chile 1960, Sumatra 2004, Japan 2011).

Focus (Hypocenter)

The exact point inside the Earth where the earthquake originates.

Epicenter

The point directly above the focus on the Earth's surface.

Elastic Rebound Theory

Stress builds up along a fault until it overcomes friction, causing a sudden release of energy.

P-Waves (Primary Waves)

Fastest seismic waves that are compressional (push-pull motion) and travel through solids, liquids, and gases.

S-Waves (Secondary Waves)

Slower than P-waves, they exhibit shear motion (side-to-side) and travel only through solids (not liquids).

Love Waves

Surface waves that cause side-to-side motion and the most damage to buildings.

Rayleigh Waves

Surface waves that exhibit rolling motion (like ocean waves) and cause the ground to ripple.

Triangulation

Requires at least three seismic stations measuring the time difference between P- and S-wave arrivals to find an earthquake's epicenter.

Intensity

Damage and effects of an earthquake, which depend on distance, depth, and local geology.

Magnitude

Energy released by an earthquake, which is an objective measure.

Mercalli Scale

An intensity scale ranging from I-XII based on human perception and damage.

Richter Scale

Measures small to mid-size quakes based on seismic wave amplitude.

Moment Magnitude (Mw)

A scale that is more accurate for mid to large earthquakes, considering total energy released.

Liquefaction

Occurs when loose, water-saturated soil behaves like a liquid due to shaking, causing buildings and infrastructure to sink or topple.

Tsunamis

Caused by underwater earthquakes (especially subduction zones), landslides, or volcanic eruptions.

Deep ocean Tsunami

Characterized by low height and fast-moving speeds of ~500-600 mph.

Near shore Tsunami

Slows down and increases in height as it approaches the shore.

Earthquake Forecasting

The process of looking at past seismic events to identify patterns.

Paleoseismology

The study of prehistoric earthquakes through geologic records.

Seismic Gaps

Areas along a fault that haven't had an earthquake in a while and may be due for one.