Earth's Interior and Seismic Telemetry

Definition of key layers, seismic wave types, and geophysical concepts based on Earth's interior telemetry data.

Seismic Telemetry

The method of decoding Earth's interior by tracking the travel and reflection of seismic waves through the planet.

Crust

The thin, rigid outer shell of the Earth, ranging from $5-70\,km$ in thickness, composed of low-density solid silicate rocks.

Mantle

A thick layer of approximately $2,900\,km$ composed of solid iron and magnesium silicates that behaves plastically over geological timeframes.

Outer Core

A fully liquid layer approximately $2,200\,km$ thick composed of high-density iron and nickel.

Inner Core

The solid center of the Earth with a radius of approximately $1,220\,km$, characterized by very high-density iron and nickel under extreme pressure.

Thermal Gradient

The approximate rate of temperature increase with depth in the Earth's crust, noted as $+25^\circ\text{C/km}$.

Earth's Radius

The distance from the surface to the center of the Earth, measuring approximately $6,371\,km$.

Mantle Paradox

The state where the mantle is classified as solid rock but flows like a viscous fluid at a rate of $\text{cm/year}$ due to temperatures between $1000^\circ\text{C} - 3700^\circ\text{C}$ and $1.4\,\text{Million Atm}$ of pressure.

Plasticity Zone

The region within the mantle where solid rock undergoes plastic deformation, allowing it to morph and flow over millions of years.

P-wave (Primary)

A compressional wave with back-and-forth particle motion that arrives first (primary) and can travel through both solids and liquids.

S-wave (Secondary)

A shear wave with up-and-down particle motion that arrives second (secondary) and can only travel through solids.

103° Dead Zone

The seismic shadow zone beyond $103^\circ$ from an epicenter where S-waves completely disappear, providing direct evidence of a liquid outer core.

Shadow Zones

Specific regions on the Earth's surface where P-waves or S-waves fail to register, revealing internal boundaries such as the liquid outer core.

Core Refraction

The sharp bending of P-waves as they enter the liquid outer core, caused by a sudden shift in material density.

Seismic Discontinuity

A boundary within the Earth where seismic wave velocity changes abruptly, such as at the Outer Core Interface.