Test 3 Material Flashcards
Why do we care about earthquakes
much of the world’s population lives in areas where earthquakes are a hazard
Earthquake Myths
-They happen in certain kinds of weather
-big earthquakes happen early in the morning
-animals can sense when they are going to happen
-California is going to fall into the sea
-the ground can open up and swallow people
-the safest place is under a doorway
-you can not prepare for them
What is an earthquake
shaking of the earth caused by a sudden release of energy
epicenter
the point on the surface directly above the focus
focus
the point where the earthquake waves are coming from
shallow focus
less than 70km
intermediate focus
between 70-300km
deep focus
greater than 300km
which depth focus is the most destructive
shallow focus are most destructive
where do earthquakes happen
at ever plate boundary type
what is a fault
fractures or cracks along which movement has occured, most earthquakes occur due to movement on faults
hanging wall
always above the fault
foot wall
always below the fault
Types of Faults
Dip Slip, Strike Slip
Dip slip fault types
normal, reverse, thrust, oblique
Dip Slip Reverse
hanging wall moves up relative to footwall, steep, accommodates compression
Dip Slip Normal
hanging wall moves down relative to footwall, accommodates extension
Dip Slip Thrust
hanging wall moves up relative to footwall, shallow, accommodates compression
Dip Slip Oblique
accommodates either tension or compression, complicated faults, some component of horizontal motion
Strike Slip
accommodates horizontal motion, transform boundary is a strike slip, cuts through the lithosphere, left and right lateral
Elastic rebound theory
describes how energy builds up and is released during an earthquake
Who developed elastic rebound theory
developed by Harry Fielding Ried
driving forces that move rocks
tectonic forces, movement of magma, sudden slip on a nearby fault, giant landslides, water pumping or injection, underground nuclear bomb tests
Displacement
occurs along fault segments
3 ways of displacement
fault creep - slow gradual, numerous earthquakes, store up energy until a major earthquake
foreshocks
small earthquakes before the major events and can happen days or months in advance
aftershocks
adjustments after a major earthquake can generate small earthquakes
earthquake triggering
earthquakes set-off far away from the main earthquake, outside of aftershock area, can trigger up to 1300km away
Can humans induce earthquakes
yes
types of waves
body waves and surface waves
types of body waves
compressional (P) waves, and Shear (S) waves
Types of surface waves
Rayleigh waves and Love waves
P-waves
pressure wave or preliminary wave, particle motion is parallel to the wave propagation direction
S-waves
Shear wave or secondary wave, particle motion is perpendicular to the wave propagation
can P waves move through the outer core
yes because you can compress a liquid and the outer core is liquid
can S waves move through the outer core
no because you can not shear a liquid
Wave speed in relation to temperature and pressure
increased temperature = decreased velocity
increased pressure = increased velocity
Rayleigh waves
named after Lord Rayleigh, also known as ground roll, very damaging to structures, counter-clockwise elliptical motion that decreases with depth
Love waves
named for A.E.H. Love, side to side particle motion that decreases with depth
How are earthquakes recorded and measured
Seismometer
Seismometer
an instrument used to measure the intensity direction and duration of an earthquake
Different seismometers
mass on a spring recording on a roll of paper, electronic sensor with digital recordings
Seismograms
a record of the ground motion at a specific location as a function of time
what is the order that the earthquake waves arrive, first to last
P-wave, S-wave, Surface waves (Rayleigh and Love)
locating earthquakes
earthquakes locations can be determined using the S-P-time from several seismograms
how many seismograms do you need to locate an earthquake
must have at least 3 records
Wadati-Benioff zones
dipping seismic zones common to convergent plate boundaries
Magnitude
a measure of the energy released during and earthquake, several different scales
Richter Magnitude
developed by Dr. Charles Richer for southern cal earthquakes recorded by a specific type of seismometer, uses the maximum amplitude of recorded S-waves
Moment Magnitude
independent of seismometer type, based on the total amount of energy released during an earthquake
Scale of Magnitude
It is logarithmic so for every 1 point increase the amplitude of the ground motion increases 10x
Earthquake Hazards
ground shaking, ground displacement, liquefaction, landslides, fires, tsunamis
what controls the level of ground shaking
-magnitude - how much energy is released
-distance - shaking decays with distance
- local soil and bedrock conditions
Would it be better to build your home on bedrock or soil/mud
rock is better, more consolidated material, shakes less
Liquefaction
mixing of soil and groundwater during an earthquake, ground becomes very soft and loses strength
Can Earthquakes be predicted
although we know where earthquakes are likely to occur, there is no reliable way to predict when an event will happen at any specific location,
Groundwater and the Hydrologic cycle
groundwater is about 22% of the world’s freshwater, comes form precipitation going through soils and sediments, and fills the open spaces in rocks
groundwater
is an important source for domesic industrial and agricultural use, also important erosion al agent and energy source
Distribution of Groundwater
zone of saturation, zone of aeration, capillary fringe, and belt of soil moisture
zone of saturation
all open spaces in sediment and rock are completely filled with water, water table is the upper limit
zone of aeration
area above water table, pore spaces mostly filled with air
capillary fringe
extends upward from the water table, groundwater held by surface tension in tiny passages between grains of soil or sediment
belt of soil moisture
water held by molecular attraction on soil particles
Properties of Materials that allow them to absorb water
porosity, and permeability
porosity
the percentage of a materials volume that is open pore space
permeability
the measure of the interconnectedness of pore spaces, ability to transmit fluid
Aquifer
porous, permeable rock that transmits water freely, high permeability, ex. gravel and sand
aquitard
rock or soil layer that does not transmit water easily, low permeability, ex clay
How does groundwater move
gravity, recharge areas, discharge areas
gravity in groundwater moving
groundwater is moved by gravity from areas of high pressure to areas of low pressure, can move up to 250 km a day or less than a few cm a day
Recharge areas
natural recharge: rainfall or snowmelt
artificial recharge: wastewater treatment plants or recharge ponds
discharge areas
natural discharge: lakes streams swamps, springs
artificial discharge: pumping from wells
types of discharge
Springs, geysers, Water wells
Springs
water table intersects earth’s surface, natural outflow of groundwater
hot springs
heated by colling igneous rocks underground, contains lots of dissolved minerals, temperature can range from 86-220F
Gysers
intermittent hot springs, erupts with great force, occur when underground chambers exist withing hot igneous rocks
geysers process
groundwater heats, expands, changes to steam and erupts
Water wells
a hole drilled or dug into the zone of saturation allowing water to seep in
problems with water wells
pumping can create a cone of depression and lower the water table
Groundwater withdrawal issues
Groundwater nonrenewable resource, Subsidence, Saltwater intrusion
groundwater nonrenewable resource
recharge less than discharge, occurs primarily when more groundwater is used than is replaced by natural processes
subsidence
water pumped from ground, ground collapses and compresses, loose grains of aquifer are packed tighter as pore spaces collapse
saltwater intrusion
excessive withdrawal in costal areas causes saltwater to be drawn into wells, contaminating freshwater supply
Groundwater contamination
serious problem due to indiscriminate practices by industry and citizens
most common sources of groundwater contamination
sewage, landfills, toxic waste disposal sites, industry, underground tanks, and agriculture
Natural filtration
water can become purified as it passes through an aquifer composed of sand or permeable sandstone, acts as a filter
what is wrong with gravel aquifers
the pore openings are too large and it does not filter well
groundwater distance and purification
groundwater my travel long distances without being cleaned
Geologic work of gorundwater
groundwater can dissolve rock
acidic groundwater
contains weak carbonic acid, and the acid reacts with calcite in limestone and the rock becomes soluble
caverns(caves)
acidic groundwater dissolves soluble rock, they form in the zone of aeration
caverns vs caves
they are the same except caverns are larger
How caves form
chemical weathering, water table drops, water-air interaction forms deposits/features
Speleothems
calcite-containing water drips from cracks in the ceiling of the cave or runs down the walls, water evaporates when encountering the air in the cave and leave behind the calcite it was carrying, calcite builds up over time
rate of growth of speleothems
1-2mm a year
Types of speleothems
Stalactites, Stalagmites, Soda Straws, Column, Flowstone
Stalactitles
icicle like cone, hangs from the celling of the cave and grows downward, water drips off tip, adding calcite
Soda Straws
a type of stalactite, delicate hollow features, build up to form more massive stalactites later on
Stalagmites
water drips onto cave floor, building up a mound of calcite, grows upward from the floor of the cave
what usually happens with stalactites and stalagmites
they often form directly over one another and they grow toward one another
Column
when a stalactite and a stalagmite grow together into one feature, connects the ceiling and floor of the cave
Flowstone
sheet-like deposits from water running down the wall of the cave
Other Cave Features
underground lakes and rivers
Underground lakes and rivers
where the water table intersects the cave
Cave environment
fairly constant temperature at about 55F, almost 100% humidity, pitch black (eyes will never adjust)
Spelunking
cave exploration
Mammoth cave
Kentucky, world’s longest known cave system, 390 miles explored with more to explore
Carlsbad Cave
New Mexico, deepest cave in the U.S. at about 750ft, one of the largest underground chambers in the world at the size of 6 football fields
Cave life
Bats, crayfish, spiders, fish, salamanders
bats
like the constant temperature and the dark
unique forms of life
crayfish, spiders, fish, and salamanders, have no coloring and no eyes
karst topography
landscaped shaped by dissolving power of groundwater
features of karst topography
irregular terrain, sinkholes, disappearing streams, karst springs
sinkholes
soluble rock is dissolved leaving shallow depressions, cavern roof collapses, due to the subsurface not being able to support the overlaying weight
disappearing streams
water disappears into underground caverns or cracks in the rock, can take unexpected paths
Characteristics of Waves
they derive their energy and motion from the wind
Parts of a wave
Crest and trough
crest of a wave
top of the wave
trough of a wave
low area between waves
wave height
vertical distance between trough and crest
wavelength
horizontal distance between crests
wave period
the time it takes for two successive crests to pass the same point
types of waves
oscillating and translational
oscillating wave
wave energy moves forward not that water itself, occur in deep water
translational wave
form in shallower water when water depth is about 1/2 the wavelength
translational wave process
speed and length of wave diminish and wave grows higher, steep wave front collapses, wave breaks along shore, turbulent water advances up shore and forms surf
wave erosion
breaking waves exert a great force
wave erosion is caused by
wave impact and pressure, abrasion by rock fragments
Wave Refraction
waves seldom approach the shore straight on but rather at an angle, when waves reach shallow water they are bent and tend to become parallel to the shore, so wave energy is concentrated against the sides and ends of headlands
headlands
land sticking out into water
consequences of wave refraction
wave erosion wears down headlands over time, eventually straitening and smoothing the shoreline, this energy also moves sand along beaches
longshore current
current is parallel to the coast, also helps move sand down the beach, sand moves with the current
erosional shoreline features
wave cut cliffs, wave cut platforms, sea arch and sea stack
depositional shoreline features
spits, baymouth bar, tombolo
spits
elongated ridge of sand extending from land into mouth of adjacent bay
baymouth bar
a sand bar that completely crosses a bay
tombolo
a ridge of sand that connects an island to the mainland or another island
2 approaches to stabilizing the shore
building structures and beach nourishment
building structures
jetties, groins, breakwaters, and seawalls
jetties
built in pairs to develop and maintain harbors
groins
built to maintain or widen beaches, constructed at a right angle
breakwaters
barrier built offshore and parallel to the coast to protect boats from large waves
seawalls
barrier parallel to shore and close to the beach to protect property, stops waves from reaching the beach areas behind the wall
beach nourishment
the addition of large quantities of sand to the beach system, very expensive and not a long term solution
Coastal classification
emergent and submergent coasts
emergent coast
develop because of uplift of an area or drop in sea level, tectonically active, tend to be erosional
features of emergent coasts
wave cut cliffs and wave cut platforms
submergent coast
caused by subsidence of land adjacent to the sea or rise in sea level, tend to be depositional
features of submergent
estuaries
