ch17 flashcards
(22 cards)
nature of waves (propagation, velocity)
Seismic waves travel outward from their source, with velocities influenced by the density, elasticity, and composition of Earth materials. Dense, rigid rocks transmit waves faster; less dense or partially molten materials slow them down
seismic reflection
The bouncing back of seismic waves when they encounter boundaries between materials with differing densities and velocities, helping to map subsurface layers
seismic refraction
The bending of seismic waves as they pass into materials of different densities and velocities, altering their direction and speed
Mohorovicic discontinuity (Moho)
The boundary between Earth’s crust and mantle, marked by a sudden increase in seismic wave velocities due to the transition to denser mantle rocks
Gutenberg discontinuity
The boundary between the mantle and the outer core, where P waves slow dramatically and S waves are blocked, creating a P-wave shadow zone
Lehmann discontinuity
A boundary within the core, marking the transition between the liquid outer core and the solid inner core, detected by changes in seismic wave behavior
P wave shadow zone
A region on Earth’s surface (approximately 103° to 142° from an earthquake’s epicenter) where direct P waves do not arrive, caused by refraction at the core-mantle boundary
S wave shadow zone
A region beyond about 103° from an earthquake’s epicenter where no S waves are recorded, indicating that the outer core is liquid and does not transmit shear waves
Benioff zones (subduction zones)
Inclined zones of earthquake foci beneath trenches at convergent plate boundaries, tracing the descent of a subducting slab into the mantle
low velocity layer (top of asthenosphere)
A region in the upper mantle, just below the lithosphere, where partially molten rock slows seismic wave velocities, indicating a weaker, more ductile layer
magnetic field
Earth’s magnetic shield, generated by the fluid motion in the outer core, which helps protect the planet from solar radiation and can be recorded in rocks
paleomagnetism
The study of Earth’s ancient magnetic field preserved in rocks, which helps reconstruct past plate movements and changes in Earth’s magnetic poles
asthenosphere
A weak, plastic layer in the upper mantle beneath the lithosphere that flows slowly, allowing tectonic plates to move above it
convection
Heat-driven circulation within the mantle; rising hot, buoyant material and sinking cool, dense material drive plate tectonics and influence Earth’s internal processes
core
Earth’s innermost layer, composed mainly of iron and nickel, divided into a liquid outer core and a solid inner core, generating Earth’s magnetic field
crust
Earth’s outermost, thinnest layer composed of continental and oceanic types, overlying the denser mantle
crustal rebound
The slow uplift of crust formerly depressed by the weight of ice sheets or other loads, as the load is removed and isostatic balance is restored
isostasy
The equilibrium state of Earth’s crust “floating” on the denser mantle, with crustal thickness and density variations compensating to maintain gravitational balance
isostatic adjustment (readjustment)
The vertical movement of Earth’s crust in response to changes in load, such as melting ice sheets or erosion of mountains, restoring isostatic equilibrium
lithosphere
The rigid, outermost layer of Earth, including the crust and uppermost mantle, broken into tectonic plates that move atop the asthenosphere
mantle
The thick layer of Earth between the crust and core, composed of solid but plastically flowing rock, where convection drives plate tectonics
seismic tomography
A method that uses seismic wave data from earthquakes to create three-dimensional images of Earth’s interior, revealing temperature and composition variations
