What is an earthquake
Vibrations (waves) produced by sudden energy releases within the earth
Elastic rebound theory
Stress - applied on either side of a fault
Strain (bending) - begins to build up
Rupture (breakage) - Strain is greater than the rock's internal strength (break)
Focus
The underground location where breaking rocks generate an earthquake
Epicenter
The earth's surface directly above the focus
Rebound
the rock snap back, which generates wave energy called an earthquake
Fault
large cracks in the earth that have measurable movement
Normal fault
One side moves down as it pulled by gravity. Prevail tension
Reverse Fault
one side of the fault moves over the other side. Prevail compression
Thrust Fault
low angle reverse fault (less than 45 degrees)
Strike slip faults
lateral slip faults
Right lateral slip fault
objects on the other side of the fault move to the right
Left lateral slip fault
objects on the other side of the fault move to the left
Active Fault
a fault that has broken the earth's surface within the last 11,000 years
measuring waves using a seismograph
recording drum to record.drum attached to the earth drum shakes. pen attached to hanging weight inertia
Body waves
they move through the body of the earth
P waves (primary waves) body waves
push-pull or compression waves
travel through solid, liquids, and gases
they bounce back when released
Fastest waves
S Waves (secondary waves) body waves
transverse or side to side waves
move at the right angles to the direction of travel
transmit only though solids
Second fastest waves
Surface waves
S waves that move side to side (Love waves) and up and down (Raleigh waves) Most destructive waves.
least fastest waves have the strongest shaking.
Ritchter scale magnitude
measure the wave amplitude (maximum pen movement on seismogram on log 10 graph
One Richter magnitude height of wave
is a 10 times increase in wave height/amplitude of s waves
One Richter magnitude in shaking energy
is a 32 times increase in shaking energy
Seismic hazards: destruction form earthquakes
Shaking hazards
Landslide hazards
liquefaction hazards
surface faulting hazards
Tsunami hazards
Shaking hazards
STRUCTURE DAMAGE
shaking intensity
duration of shaking
site geology
design of structure
FIRE
Landslide hazards
Upland Hazards: seismic energy (shaking) applies to weak natural slopes or over-weighed slopes (by poor construction design)
Liquefaction hazards
Flatland hazards especially near-coastal regions and rivers
Surface faulting hazards (ground rupture)
Active fault
no building for human occupancy within 50 feet of identified active faults
Tsunami Hazards
Seismic sea waves (no tidal waves)
how tsunami hazard form
Large movement along a fault on the ocean floor
large landslides on ocean floor
What are the first warnings of a Tsunami
Rapid withdrawal of water form beaches
five to thirty minutes later large surge of water washes onto the beach and inland
water retreats back out to sea (most destructive phase)
ten to sixty minutes later, next pulse of water comes ashore
Layered earth theory * based on seismic model
Crust - solid
Upper Mantle - solid
Asthenosphere - plastic
Lower Mantle - solid
D layer - plastic
Outer Core - liquid
inner core - solid
Seismic waves move fastest
in cold rocks
Seismic waves move slower
in hot rocks
Which is the lightest density
Crust
Which is the heaviest density
Inner Core
Layered earth theory * based on heat flow
Crust - insulator
Upper mantle - convection currents
Asthenosphere - partial melting (plastic)
Lower mantle - convection currents
"D" Layer - Partialy melting (plastic)
Outer core - convection currents
Inner core - radioactive decay releases heat (special
How does the plates of the earth's crust move
Plates of the earth's crust move as coherent, solid units with respect to each other
Plate boundaries/plate margins
are where plates of crust meet
how does Rigid plates move
move on soft asthenosphere
Divergent plate margins
where plates move apart, resulting in upwelling of magma from the mantel, cools to form new seafloor rock
What is the process of forming new seafloor rock called
sea floor spreading
Mid ocean ridge
continuous ridge formed by rising molten mantle, cools on the ocean floor and moves away form the spreading center
Rift Valleys
When spreading center develop below continents hot rising "Mantle plume" weakens continental rocks and pulls continents apart by extensional forces
Rift Valleys
Red sea
Gulf of Baja California
Atlantic ocean
Convergent Plate Margins
zones of plate convergence, where oceanic lithosphere is subducted and absorbed into the mantle
Subduction zone
region where oceanic plate descends into the mantel
Deep ocean trench
the ocean floor feature produced over a subduction zone
Types of convergent boundaries
Oceanic-continental convergence
Oceanic Oceanic convergence
Continental continental convergence
Oceanic continental convergence
The thicker, less dense continental crust "floats" over the descending thinner and denser oceanic crust
melts at 100 km to 150 depth
Newly formed magma rises to form either lines of volcanoes or lines of plutonic mountains
Oceanic continental convergence
Examples
Andean ranges
Cascade ranges
Japanese archipelago
Oceanic Oceanic convergence
when two oceanic plates converge, the colder, older, denser plate descends under the younger, warmer, lighter plate
Oceanic Oceanic convergence
Example
Aleutian islands
continental continental convergence
Neither plate will subduct beneath the other because of the low density, buoyant nature of continental rocks
Continental continental convergence
Example
Himalaya mountains
Transform plate boundaries
plates grind past each other without production or destruction of lithosphere
Transform fault
in the same level of the fracture zone
Driving mechanism theories
Convection current hypothesis
Slab pull and slab push hypothesis
Mantle plume hypothesis
Convection current hypothesis
Large convection currents in mantle carry lithosphere in a conveyor belt
Slab pull and slab push hypothesis
as oceanic slabs cool, they become denser and heavier. dense heavy slabs pull down into subduction zones
Mantle plume hypothesis
All upward convection is confined to a few mantle plumes. dense cool slab is drawn down into subduction zone by gravity
Proofs of plate tectonic theory
Polar Wandering
Magnetic reversals
Earthquake patterns
Ocean drilling
Hot spots
Polar wandering
Iron-rich grains in older rocks do not align with present magnetic poles on earth, continent must have moved
Magnetic reversals
seafloor spreading: magnetic field periodically reverses its polarity. observed in reversal strips on side of mid ocean ridges
Earthquake patterns
close association between plate boundaries and distribution of earthquakes
Ocean drilling
Age of ocean sediment increased with increasing distance from mid ocean ridges
Hot spots
mantle plumes age of chains of submerged volcanoes (seamounts) increase away form presently active volcanoes
Hot Spots
Example
Hawaiian islands
Dissolved Gases
important in volcanic erruption
Gas bubbles form
pressure is released as magma moves upward toward the surface
Magma composition
Especially silica
silicate chains
make the magma more viscous (thicker texture)
Low viscosity
fluids flow readily
high viscosity
fluids are highly resistant to flow
Magma viscosity
affects ability of gas bubbles to reach the surface
Basalts
Very fluid lavas, quit volcanic eruptions
Rhyolites
very viscous lavas, very violent eruptions
Magma temperature
Higher magma temperature results in less viscous lava
Basalt
Hotter lavas 1200 degrees makes smooth lavas
Basalt
Hawaiian basalts
Volcanic eruptions
dissolved gasses
magma composition
magma temperature
pressure
what is extruded during volcanic eruptions
Lava flows
Rhyolite flows
Basalt flows
pahoehoe flows
aa flows
Pahoehoe flows
Hawaiian smaller bubbles very fluid
aa flows
rough jagged blocks form as gas escapes form lava
Rhyolite flows
Very viscous, bubbly flows
Gases
magmas are 1 to 5 percent gases - especially water
Pyroclastic materials
Ash: fine, sand-size
cinders: pea-size
lapilli: walnut-size
blocks: larger than lapilli
is rhyolite lighter or heavier than basalt
lighter
is basalt ligher or heavier than rhyolite
heavier
Shield volcanoes
Basalt only
Typically basaltic composition
very fluid flows
Basalt is silica
poor hot
cinder cones
rhyolite mostly (some basalt)
composite volcanoes
lava flows - cinders Andesite
Mt Shasta & Mt Lassen
Steep majestic mountains; typically andesite composition
Nuee Ardent
ash flows-fast moving, glowing HOT avalanches-often air-rafted
Lahar
water-saturated volcanic ash and vocalic debris COLD
Calderas
volcanic collapse structures
size of caldera
a volcanic crater greater than 1 kilometer in diameter
Caldera form
when a partially emptied magma chamber collapses
Larger calderas form
when granitic magma chambers are close to ground surface and the roof collapses
Examples of calderas
Yellowstone
Long Valley, CA
Lava Plateaus
Extensive fluid basalt flows form fissures eruptions
Examples of Lava Plateaus
Snake River plain
Columbia river Plateau
Earth's Moon
Volcanic necks
erosional remnants of cinder cones
Cinder covering
eroded away form cinder cones
Example of cinder covering
East Mojave Desert
Intrusive igneous structures
Plutons
Plutons
Underground igneous rocks classified according to shape and size
Plutons
Dikes and Sills
Laccolths and Batholiths
Dikes
Vertical-sheet
when are vertical dikes produced
when magma is injected into fractures that cut across rocks layers
Sills
Horizontal tabular flat pluton
When are horizontal sills formed
when magma is injected along sedimentary bedding surfaces
Laccolith
Larger, lens-shaped pluton which arches overlying strata upward
When do Laccolith form
when the magma was forcibly injected
Batholith
the largest intrusive igneous bodies
What is the size of Batholith
greater than 64 square kilometers
How do rocks melt
temperature
pressure (sudden release of pressure)
role of volatiles
Temperature
Geothermal Gradient
Rising heat form mantle
Crust is an insulator
Geothermal Gradient
It gets hotter as you go deeper 20 to 30 degrees / kilometer about 1 degree F/100 feet, per book
Pressure
increases with depth
Melting
result in increase in volume, volume is held constant at depth, requires higher temperature at depth
Sudden release of pressure
lower a rock's melting temperature
Role of volatiles
very difficult to melt dry rock
in order for rocks to melt you need
water
what does volatiles cause
rock to melt at lower temperatures
Sloder Flux example
Flux removes impurities
Flux absorbs and concentrates heat
Volatiles add vapor pressure
partial melting
The spark plug
Rocks typically melt
over a range of 200 degrees C
Minerals with the lowest melting points
Melt first (example quartz)
As temperature rises Silica
sweats out of crystal structures
Partial melting tends to produce a magma that
has a higher silica content than the original rock
Distribution of igneous Activity
spreading centers
subduction zones
Intraplate Igneous Activity
Subduction Zone
Basalt becomes contaminated with silica rich continental rocks
intraplate igneous activity
Mantle plumes
Isostasy
Less dense crust Floats
Oceanic crust is
denser than continental crust
Isostatic adjustment
The crust process at funding a new level of equilibrium
Isostatic adjustment
added weight
removal weight
erosion slowly reduce mountains
Rock deformation
forces greater than rock strength
Types of deformation
Elastic deformation
Plastic deformation
stress
Strain
Strike
Dip
Elastic deformation
reversible rocks first stretch up to elastic limit like rubber band
Plastic deformation
past elastic limit flowing and folding permanent changes occur
Stress
force per unit area
strain
change in shape or size in response to stress
Compressive stress
results in rock being flattened
tensional stress
result in rock bending stretched
shear stress
stress parallel to a plane in opposite direction
Strike
compass direction of a line formed by intersection at horizontal and dipping planes
Dip
horizontal plan and incline plane
Folds
result of compressional forces
Anticlines and synclines
two most common folds
Anticlines formed
by up-folding or arching
Anticlines
oldest sediments are inside at the core of the fold youngest sediments outside
Syncline formed
by down warping into troughs
Syncline
youngest sediments are inside at the core of the fold oldest sediments outside
Example of syncline
Irvine valley
Domes
produced by up-warping old rocks are in the center
Domes shape
like a circular anticline or a double ended doubly planing anticline
Basins
produced by down-warping youngest rocks are in the center
Basins shape
like a circular syncline or a double ended doubly plunging syncline
Faults
fractures where appreciable movement has occurred
Dip slip faults movement
is mostly vertical
Hanging wall
Rock above the fault surface
Foot wall
rock below the fault surface
Normal Fault
hanging wall moves downward
reverse fault
hanging wall moves upward against gravity
thrust fault
reverse faults with dips less than 45 degrees
Strike slip faults or lateral slip faults
dominant slip is to the right or left along the fault
right lateral slip fault
the other side moves to the right
left lateral slip fault
the other side moves to the left
tensional forces pull apart forces
normal faults prevail found at the divergent plate boundaries
horst and graben structures
normal faults prevail
horst
uplifted block
Grabben
down dropped block normal faults
Compressional forces
found at the convergent plate margins
Joints
fractures with no appreciable displacement
shrinkage cracks
from igneous rocks cooling
Sheeting
unloading cracks
Fault block mountains
bounded on at least one side by high to moderate angle normal faults
Basin and ranges province
upwelling of hot mantle stretches crust 200 to 300 kilometers
Example of fault block mountains
Sierra Nevada
Teton Range
Folded mountains
most major mountain belts
Example of folded mountains
Appalachian mountains
alps
Himalaya mountains
Up-warped mountains
Caused by broad arching of crust
Examples of Up-warped mountains
Black Hills
Andirondack mountains
Mountain building
at convergent boundaries
Oceanic-continental convergent boundaries
Where oceanic crust is being subducted below continental crust
Passive continental margins
Continent is depositing sediment onto oceanic crust
Subduction zone forms
Between oceanic plate and continental plate
Parallel mountain belts form
accretionary wedge oceanic sediments are scraped form sub-ducting oceanic plate
Example of parallel mountain belts
California coast ranges
Volcanic arc
melted oceanic crust rises thorugh continental crust to form volcanic and plutonic mountain ranges
Example of Volcanic arc
Sierra Nevada
Andes Mountains
Example Ocean-Ocean convergent boundaries
Aleatian Islands Alaska
Example Continental-Continental boundaries
Himalaya mountains
Collision result in
folding continents buoyant to subduct
Mountain building and continental accretion
smaller crust fragments
pealed off sub-ducting plate
pushed onto edge of continent
distinct individual blocks are called terraces
Terrances
do not belong where they are
ridges plates move
on the soft asthenosphere
at which plate boundary is oceanic plates destroy
convergent
what structure is found between spreading ridges
transform faults
the Himalaya mountain are an example of
continental continental convergence
Hawaiian island are an example of
shield volcanoes
Southern California example of a left lateral slip fault is
Garlock
Which seismic wave travel fastest
P Waves
Tectronic plate boundaries where new seafloor is created are called
divergent boundaries
79% Nitrogen
20% Oxygen
1% Argon
Trace Gases
Ari is compose of
The crust process of finding a new level of equilibrim
Isostatic Adjustment
Which fault prevail when rocks are under tension forces
Normal Fault
Which faults prevail when rocks are under compression
Reverse Fault
A circular fold which have older rocks in the core is a
Dome
The compass direction of the intersection of a horizontal plane and a dipping plane is called the
Strike
Which has viscous thick lava
Rhyolite
Mount Lassen and Mt Shasta are which types of volcano
Composite
What is a volcanic crater greater than 1 Kilometer wide called
Caldera
An intrusive igneous rock body greater than 64 kilometer is a
Batholith
A circular fold produced by up warping so that the older rocks are in the center is called a
Dome
The present is the key to the past describes which theory
Uniformitarianism
An erosional surface with parallel strata on either side is called
Nonconformity
Fossil preservation where pores and cavities of plants or animals are filled with minerals is called
Petrification
The first step in the carbon 14 cycle is
Nitrogen 14 absorbs a neutron
Interbeded algal mats and silt are preserved as fossil
stromatolites
Half-life
5730 years