Plate Tectonics and Seismology Lecture Notes

Vocabulary practice flashcards covering plate tectonic boundary types, earthquake terminology, wave propagation, seismological measurement tools, and earthquake scaling systems.

Oceanic Divergent Plate Boundary

A boundary where rifted oceanic plates move away from each other, characterized by features such as rift valleys, volcanoes, and oceanic ridges (e.g., the Mid-Atlantic Ridge between the N. American and Eurasian plates).

Continental Divergent Plate Boundary

A boundary where rifted continental plates pull apart, creating rift valleys and volcanoes (e.g., the East African Rift Zone, Gulf of Aden rift, and Rift Lakes).

Oceanic-Continental Convergent Plate Boundary

A boundary where an oceanic plate collides with and subducts beneath a continental plate, forming a subduction zone, deep-sea trench, and volcanic arc (e.g., the Nazca Plate subducting beneath South America near Ecuador to create the Andes Mountains).

Oceanic-Oceanic Convergent Plate Boundary

A boundary where two oceanic plates come together, producing a subduction zone, an oceanic trench, and a volcanic island arc (e.g., the Aleutian Islands where the Pacific Plate subducts near Alaska).

Continental-Continental Convergent Plate Boundary

A boundary where two continental plates collide, pushing rock upward to form folded mountains (e.g., the Himalaya Mountains formed by the collision of the Indian Plate and Eurasian Plate).

Continental-Continental Transform Plate Boundary

A boundary where plates slide laterally past one another along a strike-slip or lateral fault (e.g., the San Andreas Fault in California).

Earthquake

A vibration of the Earth caused by a rapid release of energy, typically occurring along tectonic plate boundaries, subduction zones, and faults, or produced by volcanic activity.

Focus (Hypocenter)

The subsurface area inside the Earth where an earthquake actually originates and from which shock waves radiate outward.

Epicenter

The point on the Earth's surface located directly above the earthquake's focus (derived from the prefix 'epi' meaning outer skin).

Stick-Slip Motion

A mechanism in which two rock masses attempting to slide past each other stick due to friction and surface irregularities, bend under accumulating stress, and then violently slip when the stress exceeds friction, releasing stored energy as seismic waves.

Body Waves

Seismic shock waves that travel through the interior of the Earth, divided into primary waves ($P$-waves) and secondary waves ($S$-waves).

Surface Waves

Seismic waves that spread across the Earth's surface; they travel the slowest of all seismic waves and arrive last at recording stations.

Primary Waves (P-waves)

Compressional body waves that travel through both solids and liquids; they travel about $1.7$ times faster than secondary waves, making them the fastest to travel and the first to arrive at distant locations.

Secondary Waves (S-waves)

Shear body waves that travel only through solids; they move slower than primary waves and arrive second at seismograph stations.

Seismograph

An instrument designed to detect, measure, and record seismic waves generated by earthquakes.

Seismogram

A paper or digital record produced by a seismograph displaying the arrival times, types, and intensity of seismic waves.

P-S Interval

The measured time difference between the arrival of the first primary wave ($P$-wave) and the first secondary wave ($S$-wave) at a seismic station, used on a Travel-Time Graph to find distance to an epicenter.

Travel-Time Graph

A reference graph used by seismologists to translate the elapsed time between the arrival of $P$-waves and $S$-waves ($P\text{-}S$ interval) into the physical distance to an earthquake's epicenter.

Triangulation

The method of determining the exact location of an earthquake's epicenter by drawing distance-radius circles around at least three separate seismographic stations and identifying their point of intersection.

Magnitude

A quantitative measure of the strength of an earthquake determined from seismographic data.

Richter Scale

A well-known earthquake magnitude scale based on actual ground shaking, where every whole-number increase represents a 10-fold increase in ground shaking; the highest earthquake recorded on this scale was $8.9$.

Moment-Magnitude Scale (M.M.S.)

The most commonly used and accurate scale among seismologists for measuring earthquake magnitude; ranked the strongest recorded earthquake (in Chile) at $9.5$.

Intensity

A qualitative measure of an earthquake's strength based on its observed effects on people, human-made structures, and the natural environment.

Modified Mercalli Scale

An intensity scale used in the United States that rates earthquakes from imperceptible shaking to catastrophic destruction based on effects and damage observed near the epicenter.

Circum-Pacific Belt

Commonly known as the 'Ring of Fire', a zone of volcanic arcs and volcanic island arcs encircling the Pacific Ocean basin where multiple plates subduct, producing the vast majority of global earthquakes.