Plate Tectonics (GLY 326) Practice Flashcards

A comprehensive set of vocabulary flashcards covering the basic definitions of plate tectonics, Earth's internal layers, plate boundary types, faults, and seismic terminology.

Plate tectonics (theory)

The theory that Earth's outer shell is divided into several plates that glide over the mantle, acting like a hard and rigid shell compared to the rocky inner layer above the core.

Core

The center of the Earth, divided into a solid inner core of $1,216\,km$ thickness and a molten outer core of $2,270\,km$ thickness.

Mantle

The layer surrounding the core with a thickness of $2,900\,km$, made mostly of silicates of magnesium and iron; its uppermost section behaves like melted plastic.

Lithosphere

The rigid outermost layer of the Earth that combines the crust and the uppermost solid mantle.

Asthenosphere

The partially molten part of the upper mantle where the tectonic plates are able to move.

Inner Core properties

Solid Iron and Nickel with a density of $17\,g/cm^3$ and temperatures between $4,000-4,700^\circ\text{C}$ generated by radioactive decay.

Outer Core properties

Molten Iron and Nickel with a density of $12\,g/cm^3$ and temperatures between $3,500-4,000^\circ\text{C}$.

Oceanic crust

A thin layer ($7-8\,km$) composed of dense (mafic) iron magnesium silicate igneous rocks, such as basalt, with a density of $3.3\,g/cm^3$.

Continental crust

A layer ($35-90\,km$) composed of less dense (felsic) sodium potassium aluminium silicate rocks, such as granite, with a density of $2.67\,g/cm^3$.

Faults

Planar rock fractures along which movement has occurred.

Normal Faults

Rock fractures where the hanging wall block moves down relative to the footwall block.

Reverse Fault

A dip-slip fault, particularly along convergent boundaries, associated with powerful earthquakes of magnitude $8$ or more.

Convergent boundary

A plate margin formed when two plates collide with each other, such as the Indo-Australian Plate colliding with the Eurasian Plate to form the Himalayas.

Divergent boundary

A plate margin formed when plates separate from each other, leading to features like sea-floor spreading at the Mid-Atlantic Ridge.

Transform boundary

A plate margin where plates slide alongside each other, exemplified by the San Andreas Fault in California.

Triple junction

A point where three plates are pulling away from one another, such as the Afar Triangle where the Arabian Plate meets two others in East Africa.

Seismicity

The worldwide or local distribution and measure of the frequency of earthquakes in space, time, and magnitude.

Earthquake

The result of a sudden release of energy in the Earth's core that creates seismic waves, often due to movements within the crust or volcanic action.

Richter Magnitude Scale

A scale that gives a single numerical value to quantify the amount of energy released during an earthquake.

Modified Mercalli Intensity Scale

A scale ranging from I to XII used to measure the severity of an earthquake based on its effects on the earth's surface and humans.

Seismograph

A sensitive pendulum instrument used to detect and record the shaking of the Earth.

Seismogram

The output of a seismograph, which can be produced on paper or recorded digitally by computers.

Epicenter

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

Focus (Hypocenter)

The point within the earth where an earthquake rupture starts.

Aftershock

An earthquake that occurs after a mainshock in the same region, representing the crust adjusting to the effects of the initial displacement.

Earthquake swarms

Sequences of earthquakes striking a specific area in a short period where no single earthquake is clearly the mainshock.

Soil liquefaction

A secondary effect of shaking where water-saturated granular material temporarily loses strength and transforms from a solid to a liquid.

Tsunami

Long-wavelength sea waves produced by abrupt water movement, typically traveling at $600-800\,km/h$ and caused by subduction earthquakes of magnitude $7.5$ or higher.