Exam 1 Review Flashcards
What are the compositional layers of the earth?
Crust Upper Mantle (includes transition zone) Lower Mantle (includes D'') Outer Core Inner Core
Crust
- thicknesses
- chemical composition
Continental Crust
~20-70 km thick
-mainly granitoid
Oceanic Crust
~7 km thick
-gabbro (basalt)
Upper Mantle
- thicknesses
- chemical composition
70-660 km
Peridotite (~75% olivine (olivine structure), ~25% pyroxine)
Transition Zone
- thicknesses
- chemical composition
410-660 km
Mg2SiO4 (spinel structure)
Lower Mantle
- thicknesses
- chemical composition
660-2891 km
Solid - perovskite
D’’
- thicknesses
- chemical composition
~2741-2541 - 2891 km
Solid - Denser post-perovskite
Outer Core
- thicknesses
- chemical composition
2891-5150 km
Liquid - Fe, some lighter elements (S , Ni)
Inner Core
- thicknesses
- chemical composition
5150 - 6371 km
Solid - Mostly Fe, Some Ni
What are the mechanical layers of the earth?
Lithosphere Asthenosphere Mesosphere Outer Core Inner Core
Lithosphere
- thickness
- Mechanical Behavior
- Includes what compositional layers?
Upper 100 km
Hard Solid
Crust and some of the upper mantle
Asthenosphere
- thickness
- Mechanical Behavior
- Includes what compositional layers?
100-350 km
Soft Solid
In the upper mantle
Mesosphere
- thickness
- Mechanical Behavior
- Includes what compositional layers?
350 - 2891 km
Hard Solid
Some of the upper mantle, transition zone, and lower mantle including the D’’ layer.
Outer Core
- thickness
- Mechanical Behavior
- Includes what compositional layers?
2891 - 5150 km
Liquid
Outer Core
Inner Core
- thickness
- Mechanical Behavior
- Includes what compositional layers?
5150 - 6371 km
Hard Solid
Inner Core
What are the boundaries within the earth?
- MOHO
- D’’ discontinuity
- Core mantle boundary
- Inner core boundary
MOHO
- type of boundary
- location
compositional
Between crust and mantle
D’’ discontinuity
- type of boundary
- location
compositional
Between ‘lower mantle’ and D’’
Core mantle boundary
- type of boundary
- location
compositional and mechanical
Between mantle and core
Inner core boundary
- type of boundary
- location
compositional and mechanical
Between outer core and inner core
What are the types of seismic waves?
Body waves and Surface Waves
Define Seismic Wave
Disturbances in the Earth, propagate as waves
Define Body Wave
Propagate within a medium (travel through body of the earth)
Define Surface Wave
Propagate along the surficial boundary of a medium (confined to surface of earth, created by constructive interference of body waves at the surface)
What are the types of body waves?
P-waves and S-waves
What is a P-wave?
Primary (P or compressional waves)
Why are they called P-waves?
They are called primary because they arrive first.
How do P-waves propagate?
They propagate by a series of compressions or dilations of a material.
What is the particle motion of a P-wave?
The particle displacement is parallel to the direction of propagation.
What can P-waves travel through?
Both Solids and Liquids
DRAW A DIAGRAM FOR P-WAVE PARTICLE MOTION
SEE HANDOUT L04
Give an analogy as to how P-waves move
Like a slinky
What is the equation for the velocity of a P-wave?
Vp = sqrt((k + 4u/3)/p) (see study guide)
Fill in the blank: The more incompressible or rigid the material is, then the __________ the P-wave will travel through it.
FASTER
What is an S-wave?
Secondary (S or shear) wave
Why are they called S-waves?
These are called secondary because they arrive behind the P-waves.
How do S-waves propagate?
These propagate by shearing the material back and forth.
What is the particle motion of an S-wave?
Particle displacement is perpendicular to the direction of propagation.
What can S-waves travel through?
only solids
Why don’t S-waves travel through liquids?
S waves are dependent on shear modulus and in liquids the shear modulus is zero.
Why can S-waves be divided into two components? What are they?
Because particle motion is perpendicular to the propagation direction.
SH-motion
SV-motion
What is SH-motion?
Parallel to the horizontal axis
What is SV-motion?
Perpendicular to SH-motion.
DRAW A DIAGRAM FOR S-WAVE PARTICLE MOTION
See handout L04
What is the equation for S-wave velocity?
Vs=sqrt(u/p) see study guide handout
What happens to the velocity of P and S waves with increasing depth?
With increasing depth, the pressure increases and most materials become more compact.
As this happens generally k and u increase, which implies that Vp and Vs also increase.
BUT an increase in depth usually is accompanied by an increase in density.
This causes Vp and Vs to decrease.
In general, the increase in k and u is much greater than the decrease in p.
So we get an overall INCREASE in Vp and Vs.
What are the two types of surface waves?
Rayleigh Waves (ground roll) Love Waves
What creates Rayleigh Waves?
Created by a combination of P- and Sv- wave motion (created by constructive interference of P and SV waves at the surface)
What is the particle motion of Rayleigh Waves?
Particle displacement is retrograde elliptical.
DRAW A DIAGRAM FOR RAYLEIGH WAVE MOTION
See L04 and class review notes
What is the velocity of Rayleigh Waves?
Vr=0.9Vs