Flashcards in Chapter 4 Layers, Convection and Buoyancy Deck (21)
changes reflect variations in density and composition
Seismic waves can change speed, frequency, and intensity depending upon the medium in which they travel. These changes reflect variations in density and composition throughout the interior of the Earth.
that travel along an interface or surface between two layers
that travel uninterrupted through the Earth
P-waves or primary waves
that are compressional waves where particles move in the direction that the energy is traveling
S-waves or secondary waves
that are shear waves where particle motion is perpendicular to the direction of energy. In addition, S-waves do not travel through liquid.
Composition of the rocks
When discussing the composition of rocks throughout the Earth, we are referring to the chemistry of the rocks to distinguish different layers.
a solid mass mostly made of iron and nickel.
Outer core and geodynamo
liquid iron and nickel from which the magnetic field is derived due to the motion of fluids, otherwise known as the geodynamo. The core also contains sulfur, silicon, oxygen, and carbon.
this can be broken into a couple of layers, the upper being more solid than the lower more viscous and pliable layer
the uppermost layer of the Earth that varies in thickness, the oceanic crust being thinner than the continental crust
Properties of rocks
When discussing the properties of rocks subject to different temperatures or pressure, we use the lithosphere and asthenosphere.
behaves rigidly and includes the crust and the upper mantle.
behaves in a ductile fashion and flows over time. This part of the mantle roughly corresponds to the middle of the mantle
is the mantle region below the asthenosphere but above the outer core
is the force that drives plate tectonics
is the heat engine to convection.
(or ridge push) – rising magma will push up against an ocean ridge to elevate it slightly over the surrounding oceanic plate. The elevated material acts to push the plate away from the center of the ridge. This is only a small contribution (5-10%) of the total force acting to move the plate.
the weight of the subducting portion of the oceanic plate acts to drag the remaining portion of the plate down with it. This is the greatest force acting on moving a plate.
the horizontal force of the continental plate that is driven by convection pushes against the subducting slab and acts to push it down the subduction zone. This is a complex force and depends on the nature of the contact between the plates. It is the smallest of the three forces.
is a force that opposes gravity and describes how well something floats when placed in a fluid.