Earth’s Interior
How we know what’s inside.
1. Astronomy - calculated density of the Earth does not correspond to the density of rocks at the surface. The Earth must be layered.
2. Drilling through the crust – not possible.
3. Earth’s delivery service
-Kimberlite Pipes - occurs in the Earth's crust in vertical structures, pipes. They are formed deep within the mantle, at
between 150 and 450 kilometers depth, from anomalously enriched exotic mantle compositions, and are erupted rapidly and
violently, often with considerable carbon dioxide and other volatile components. They deliver rocks from throughout the
crust to the surface where they can be studied.
-Ophiolites - a section of the Earth's oceanic crust and the underlying upper mantle that has been uplifted or emplaced to be
exposed within continental crustal rocks.
4. Seismic data
- Elastic rebound theory - Describe the release of stored energy as two tectonic plate move past each other. The plates
rebound to their original shape.
- Seismograph - work on the principle of inertia. A weight which is secured to the ground and suspended over a paper stays
motionless and the paper is mover during an earthquake.
Types of Seismic Waves
Body Waves - travel thru the Earth
- P waves
- primary waves
- result from alternating compression and expansion of material
- also known as a compressional wave
- highest velocity seismic wave (4mi/s)
- travel through solids, liquids, and gases
- S waves
- also known as secondary waves or shear waves
- slower than P waves (2mi/s)
- greater amplitude (more shaking) than P waves
- can only pass through solids, not liquid or gas
- cause most of the damage during earthquakes
Travel of Seismic Waves
When seismic waves encounter a boundary between two layers of the Earth, they will reflect and refract.
Reflection – return of wave off a boundary (bounce back)
Refraction – change in direction and velocity of the wave
Seismic Shadow Zones - Area of the Earth that cannot record an earthquake because of the way seismic waves are reflected and
refracted and because the S wave dies off in liquid layers and provide us a glimpse of the internal layering of the earth.
Earthquake magnitude
Richter scale – (1-10, logrithmic) measure of the
amplitude (amount of energy released) during an
earthquake.
Mercalli scale – (I – XII) measure of the destruction.
Locating the epicenter of an earthquake
Because the P wave travels 2 miles per second faster than the S wave, the farther they travel the farther apart they become.
The distance the earthquake occurred from any locating station can be calculated and a radius drawn around the locating
station. If THREE locating stations do this, the circles will intersect when the earthquake occurred.
On the left are layers of the Earth defined by chemical
properties.
On the right are layers defined by seismic data.
The parts of the Earth's interior
Crust – solid
Asthenosphere – liquid
Mantle – solid
Outer Care – liquid
Inner Core – solid
S-wave shadow zones form as wave meet the boundary between
the mantle and the outer core at a shallow angle and get reflected
away. Those waves that meet the boundaries at a sharp enough
angle to penetrate die out in the liquid of the outer core.
P-wave shadow zones form as wave meet the boundary between
the mantle and the outer core at a shallow angle and get reflected
away. Those waves that meet at a sharp enough angle to enter are
refracted (bent) as they pass into and out of the cores. There are
regions of the Earth that cannot receive the P-waves.
Structural Geology - Faults
Stress – the force acting on a surface.
Strain – deformation resulting from stress.
Deformation –change in shape or volume of a rock in response to stress.
Stresses
Uniform – Compressional, same in all directions
Differential – applied force is greater in one direction. For faults or folds to occur, the stress must be diferential.
Compressional, pushing together
Tensional, pulling apart
Shear, acts parallel to a surface
Deformation
1. Elastic – nonpermanent, rock returns to original shape
Elastic limit – the point beyond which permanent deformation occurs.
2. Ductile – permanent change in the shape by bending or flowing
3. Brittle – permanent change in the shape when the material fractures or cracks.
Factors affecting deformation
1. Temperature – as the temperature increases, materials become more ductile.
2. Confining pressure – as pressure increases (weight if overlying rock), materials become more ductile.
3. Rate of deformation – if stress is applied rapidly, rocks will tend to be brittle.
4. Composition of the rock – at the same temperature and pressure, some rocks will be more brittle than others.
Strike – the orientation of a line of intersection between a rock layer and a horizontal plane.
Dip – the angle between a tilted surface and a horizontal plane.
Faults
1. Dip – Slip
a. Normal fault – tensional forces (pulling apart), hanging wall moves down relative to footwall.
b. Reverse fault – compressional forces (pushing together), hanging wall moves up relative to footwall.
2. Strike – Slip – both of these are caused by shear stress.
a. right – lateral
b. left - lateral
Folds
1.
Rules for folds (causes for each)
a. Anticline (compression)
1. Age - oldest rocks at axis
2. Dip - beds dip away from axis
3. Plunge - fold plunges toward the closed end of the outcrop
b. Syncline (compression)
1. Age - youngest rocks at axis
2. Dip - beds dip toward the axis
3. Plunge - fold plunges toward the open end of the outcrop
c. Monocline (basement block faulting)
1. has only one dipping limb.
d. Dome (intrusions)
1. Age - oldest rocks at center
2. Dip - beds dip away from center
e. Basin (subsidence)
1. Age - youngest rocks at center
2. Dip - beds dip toward the center
Surface Water
Water Storage Reservoirs
Oceans
Icecaps and Glaciers
97 %
2%
Running Water - (stream flow)
1. Laminar Flow - particles flow in a straight-line path, parallel to the stream channel
2. Turbulent Flow - water moves in an erratic fashions characterized by swirling, whirlpool-like eddies.
Controlling Factors
1. velocity of flow
2. roughness of the channel bottom
Discharge - the amount (volume) of water pasting a certain point in a given amount of time. (m3/sec, MGD, cfs, gal/min.)
Gradient - the vertical drop of a stream over a fixed distance. Streams typically have a higher gradient (steeper) at their head (the
region where the stream begins), and have a lower gradient (less steep) at their mouth (the area where they empty into a larger body of
water.
Stream Erosion
Cut-bank - Water moves fastest around the outside of a meander (bend in the river). This is where material is eroded.
Point bar - Water moves slow around the inside of a meander. This is where material is deposited
Transport and Deposition of Sediments
Transported Loads
1. Suspended load – silt and clay
2. Saltation – sand-sized particles
3. Bed loads – larger gravels
Saltation – particle transport by jumping or skipping along the bottom.
Deposits within the stream valley
Bars - temporary channel deposits of sand, gravel, and coarser components of the stream’s load.
Point Bars - bars which occur on the inside of a bend.
Alluvium – all material deposited my streams. This is sort material.
Braided stream – interwoven stream channels caused by accumulated sediments choking off the channel and the stream splitting into
several smaller streams. This occurs when the load supplied to a stream exceeds its capacity to transport it and the material settles to
bed of the stream.
Floodplains
Natural Levee – built by successive floods which deposit the coarser fraction of their load as water velocity decreases when it leaves
the channel and enters the floodplain.
Backswamps – the poorly drained area behind the levee.
Yazoo Tributaties – rivers within the floodplain which drain the backswamp and which parallel the main channel.
Deltas and Alluvial Fans
Distributaries occur where the main channel divides into several smaller ones.
Delta forms when a stream enters an ocean or lake and velocity decreases.
Alluvial Fans develop where a high-gradient stream leaves a narrow mountainous valley.
Drainage Patterns
1.
2.
3.
Dendritic - Horizontal strata
Radial – around a topographic high
Rectangular – a heavily jointed area
Stages of stream development
1. Youthful – characterized by downcutting and a V-shaped valley.
2. Maturity – once the stream has sufficiently lowered its gradient, it begins to erode laterally, producing a
wide valley.
3.Old Age – the valley is cut several times wider than the depth of the meander belt.
Groundwater
Zone of aeration - the area above the water table where openings are in the material are filled with air.
Capillary fringe – narrow zone just above the water table where water is pulled upward.
Water table – the upper level of the saturated zone. Separates the zone of aeration from the zone of saturation.
Zone of saturation – the zone where all opening are filled with water.
Porosity – the volume of open spaces in rock or soil.
o pore spaces`
o fractures (joints)
o vesicles
o cavities
Permeability – a measure of a material’s ability to transmit water.
Aquifer – a region in the subsurface which stores and transmits water in a quantity and quality great enough to be useful. This region
of the subsurface must have both POROSITY and PERMEABILITY to qualify as an aquifer.
Aquitard – a layer of the subsurface which retards drastically slow down) the flow of water.
Aquiclude – a layer of the subsurface which excludes (stops) the flow of water.
Unconfined Aquifer – is a region in the subsurface into which any rain or surface water can directly infiltrate and recharge the
aquifer.
Confined aquifer – a layer in the subsurface which meets the criteria for being an aquifer and which is sandwiched between two
aquicludes. This creates pressure in the aquifer.
Artesian well – a well drilled into the pressurized region of a confined aquifer. The water flows freely from this well and does
not need to be pumped.
Effluent Stream – water moves from the ground up into the river.
Influent Stream – water sinks from the river into the ground.
Cone of Depression – a cone-shaped depression of the water table surrounding a well after
Karst – geologic features created by the dissolution of limestone bedrock.
 Dissolution cavities
 Caves
 Sink holes
 Sinking streams
pumping.