Earth's Interior & Geophysical Properties

Flashcards reviewing Earth's interior structure, seismic waves, and geophysical properties, including the crust, mantle, core, isostasy, gravity, magnetic fields, temperature, and heat flow.

Geophysics

The branch of geology that studies the interior of the Earth.

Seismic waves

Vibrations from a large earthquake that will pass through the entire Earth.

Seismic reflection

The return of some waves to the surface after bouncing off a rock layer boundary.

Seismic refraction

Bending of seismic waves as they pass from one material to another having different seismic wave velocities.

The Crust

The outer layer of rock that forms a thin skin on Earth’s surface

The Mantle

A thick shell of dense rock that separates the crust above from the core below

The Core

The metallic central zone of the Earth

Oceanic Crust

Composed of mafic rocks (basalt); seismic waves travel about 7km/sec through it.

Continental Crust

Composed of felsic rocks (granite); seismic waves travel about 6 km/sec through it.

Lithosphere

Crust and upper mantle together, the brittle outer shell of the Earth that makes up the tectonic plates.

Asthenosphere

A plastic low–velocity zone where seismic wave speeds abruptly decrease.

Seismic shadow zones

Specific areas on the opposite side of the Earth from large earthquakes that do not receive seismic waves.

P–wave shadow zone

Explained by refraction of waves encountering core-mantle boundary (103–142° from epicenter).

S–wave shadow zone

Suggests outer core is a liquid (≥103° from epicenter)

Composition of the Core

Iron–Nickel alloy mixed with small amounts of lighter elements.

D” layer

Layer at the base of the mantle, marked by great changes in seismic velocity, density and temperature.

Ultralow–velocity zone (ULVZ)

Hot, molten metal pressed against solid rock at the core-mantle boundary.

Isostasy

Equilibrium of adjacent blocks of brittle crust “floating” on upper mantle.

Isostatic adjustment

Rising or sinking of crustal blocks to achieve isostatic balance.

Crustal rebound

Rise of crust after ice sheet removal

Gravitational force

Determined by the mass and the distance between objects

Gravity meters

Detect tiny changes in gravity at Earth’s surface related to total mass beneath any given point

Magnetic field

A region of magnetic force that has north and south magnetic poles.

Magnetic reversals

Times when the poles of Earth’s magnetic field switch, recorded in magnetic minerals

Paleomagnetism

The study of ancient magnetic fields in rocks allows reconstruction of plate motions over time

Magnetic Anomalies

Local increases or decreases in the Earth's magnetic field strength.

Magnetometers

Instruments used to measure local magnetic field strength; can detect metallic ore deposits, igneous rocks, and thick layers of non–magnetic sediments beneath Earth’s surface.

Geothermal Gradient

Temperature increase with depth into the Earth which tapers off sharply beneath lithosphere.

Heat flow

The gradual loss of heat through Earth’s surface