Test 2 Flashcards
1906 earthquake
Richter magnitude: 8.3
700 dead prolly closer 28-30k
400-524 million in losses 6-8 bill in 2009 dollars
Earthquake definition
A rapid release of energy as strain (fractures/faults) due to stress (usually tectonic)
-energy in waves
Hypocenter
(Focus)
The source
Epicenter
Is location of focus
-movement along faults
Where do quakes occur?
Plate boundaries -convergent -divergent -transform Interplate boundaries -new Madrid zone -Virginia, US 2011
Elastic rebound theory
-natural way earthquakes happen
Hf Reid suggested based on research done on the 1906 quake
- Rocks on both sides deform from stress
- Rocks bend and store elastic energy
- Stress overcomes strength of rocks
- MOVEMENT occurs along the fault line
Manmade Causes of an earthquake
Crustal loading (building a reservoir) —Hoover dam 1930s 600 quakes in 10 years after construction Deep water disposal —Rocky Mountains Arsenal 1962-2965 (M4 quakes) pumped waste fluids into a well into fractured metamorphic rock Nuclear explosions (subsurface - Nevada test site)
Fault
A fracture upon which displacement (movement) is observed
Two sides of the fault
Foot wall: stand on
Hanging wall: hang from
Normal fault versus reverse fault versus reverse thrust fault
Foot wall goes Up:Normal (FUN)
Foot wall goes Down >45:Reverse (FDR)
Foot wall goes Down <45: Reverse thrust (FDR)
Strikeslip Fault
Surface - no foot wall or hanging wall
Defined by relative movement as seen across the fault
Fault zones
Divided into segments
Fault segments
Based on related seismic events
Active faults
Must have shown movement within the last 10,000 years
Foreshock
Caused by slippage along the Fault surface hours or days before the earthquake
Aftershocks
refer to continued movements or adjustments along the fault, or connected faults hours to months or maybe years after the quake
Seismology
The science of studying earthquakes (seismic) waves
Two kinds of seismic waves
- Body waves
- travel through the earth at varying velocities depending on the type of rock or stat of matter - Surface waves
- waves which reach the surface move in particular waves. These waves do all the shaking and damage
Two types of body waves
- P waves (compressional waves)
- p waves push and pull in the direction
- they are moving (propagation)
- they are fastest (first waves on seismogram)
- they move through solid, liquid, and gas - S waves (shear waves)
- these waves move vertically perpendicular to the direction they’re traveling (propagation)
- they do not travel through liquid
- they arrive second on seisogram
Two types of surface waves
- Rayleigh waves (r waves )
- roll as they progress along the surface - Love waves (l waves)
- like S waves they move perpendicular to the direction they are traveling, but horizontally
How are waves affected by the material they move through
Weaker the rock/sediment = seismic waves are amplified (increased)
Seismograph
- record seismic waves as they occur
- the writing instrument (today electromagnetically) is separate vroom the instrument and so records as the machine shakes with the waves
- the result is a seismogram
What are seismogram measured in
Amplitude
Time
How a seismogram works
- Seismic waves from an earthquake move out concentrically from the focus and arrive at distant seismographic stations at different times
- Because p waves travel faster than S waves, the interval between their arrival times increases with distance
- By matching the observed interval to known travel-time curves, a seismologist can determine the distance from the station to the quake epicenter
How many seismographs do you need to locate the epicentr
Total of three or more
Magnitude
The amount to energy that is generated during an earth wake but it depends on which scale is used
Richter magnitude scale
Developed by Charles richter in 1935 and basked p the amplitude of the highest recorded magnitude
Amplitude in Richter scale
-each level produces 10x mor amplitude the;magnitude before, so the amplitude of a magnitude 3 is 10 times higher than 4
Energy in the Richter scale
The scale is logarithmic
-each level produces 32x more amplitude than the magnitude before
—a magnitude of 5 is 32x32 times higher than that of a 3
Momentum magnitude scale
The difference between moment magnitude and the Cale is the addition of more data: fault surface area and wave length of displacement
Earthquake intensity scale
scale 1-7 depending on effect of quake
Shaking and rupture
Surface waves often cause ru
Tires at the surface (not to mention destruction of urban areas-producing a fault surface called a fault scarp
Liquefaction
We mentioned it in soils: too much water in the rock/sediments May liquefy in response to seismic waves (sensitivty)
Sand boil
Sand mixed with water liquefies during quakes and often water is ejected out of the ground forming sand/mud holes
Landslide
On hills where the rock/soil strength is overcome by the shaking rockslides occur
-mount Huascaran shook and a large part (rock and ice) collapsed burying the city of Yungay, Peru killing >20k people in 1970
Earthquakes cause
- Liauficatoon
- Sand/mud boiling
- Landslides
- Fires and disease
- Tsunami
Tsunami
Japanese for large harbor waves, are gigantic waves generated by:
-vertical displacement from subsea earthquakes
-large subsea landslides
-extraterrestrial impacts
—-third largetst earthquake December 26, 2004 Indonesia magnitude 9.0-9.1 earthquake, displacement was about 15 m along 1200 km to the WSW and caused tsunami waves and triggering quakes as far as Ak killing about 230 k people
Tsunami characteristics
Avg speed-713 km (>500 km/hr)
Save length: >100 km, shortens as you near the beach
Wave heigh on impact: increases near the shore, up to 30 meters, largest was from a land slide at 524 meters
More than one wave: first not always the last
Seismic risk is analyzed by
Geology-tyE of rocks determine how seismic waves move through
Seismology- recent seismic activity
Paleosiesmology- faulting reforged in the rock record
Geodesy-tectonic plate movement as recorded by gas satellites
What tells us about the history of a fault and frequency of quakes
Regions faults in rock record along with defending the age of the rocks
Precursors to earthquakes
- foreshocks
- deformation of the ground
- emission of radon (Rn) gas
- seismic gaps
- anomalous animal behavior
What to do to prepare for an earthquake
-practice duck voter and hold
-education: is your house ready?
—chimney reinforced?
—house securely attached to foundation
—heavy house items secure
—cover windows with Mylar
—water/gas heater fastened
During and after an earthquake
Be aware of how seismic waves hit(p then s)
- remain calm-crouch under a desk/table or stand in a strong doorway
- wait until shaking is done
- check on family members
- check for gas leaks/fire
Volcanic seismic waves
Tremors and harmonics
Seismic waves produced by volcanoes
Shallower often with harmonic tremor waves
How many volcanic eruptions per year
50-60
20k lives lost in the last 20 years
Where are the most active volcanoes
Japan, Mexico, Phillipeans, and Indonesia
Famous historical eruptions
- August 27 1883 itAly
- Vesuvius: precursors earthquake in Feb 63 ad, many tremors in the days before, eruption 73 AD Death toll: 300 body casts 3360-10k dead
- Krakatoa: precursors earthquakes up to 3 months prior, venting steam may 1883, erupted August 27 1883 death toll: official 36,417 but prolly around 120k
Plinian eruption
Mount Vesuvius eruption named after Piny the Elder who recorded the eruption
Cultural effects of eruptions
Scream=Krakatoa by edvard munch
The last da of Pompeii=Vesuvius by Karl briullov
Vesuvius and Krakatoa
Vesuvius: last big eruption March 1944. City surrounds the crater, obvi no one lives there tho.
Krakatoa 2008 Eruption, people are warned to stay 3 km away
Tectonic factors controlling volcanic eruptions
Where the volcano is located in relation to plate boundary
Convergent: yes (mostly around the pacific ring of fire
-continental ocean: subduction zone continental volcanic arc
-ocean ocean: subduction zone volcanic island arc
Divergent: yes (where new crust is formed)
Tansform: no
Magmatic factors controlling volcanic eruptions
(Lava at surface)
- Viscosity (how fast it flows) controlled by composition of lava
- high silica (70%) high viscosity (felsic-rhyolite) copper color
- intermediate silic (60%) intermediate viscosity (intermediate andesite)white color
- low silica (50%) low viscosity (mafic-basalt)blackcolor - Temp of magma
- high temp=low viscosity
- low temp= high viscosity - Dissolved gasses in magma
- high viscosity doesn’t let air bubble out
- low viscosity lets air bubble out easily
Factors controlling explosiveness of eruption
- Composition
Lower silica, lower viscosity, less explosive
More silica, higher viscosity, very explosive - Temp
Higher t, Lower viscosity, less explosive
Lower t, higher viscosity, more explosive - Dissolved gasses
Magmatic gasses expand as they get closer to the service, reduces mobility, increasing gasses that can’t escape increased pressure=very explosive
Lava flows
- Basaltic lava flow (most studied) low silica content
- pahoehoe: ropy texture, indicates HOT less viscous lava
- AA: blocky jagged, more viscous
- Lava tubes: a cooled crust forms on top of basalt flow. A conduit, lava tube, developed in the flow, tubes prevent cooling causing flowing for hours, - Rhyolitic/andesitic flow high silica content
- very viscous blocky lava CLOSE to the vent usually (becomes rubble or can block the vent
Types of volcanoes
- Shield volcanoes
- Cinder cones
- Composite-strato
- Fissures
Shield volcanoes
- broad slightly dome shaped
- oceanic crust (basaltic lava)
- largest type
- mild eruptions of high volumes of lava
- Mauna Loa on Hawaii
- pahoehoe and Aa
- found intraplate oceanic crust OR divergent boundaries
Cinder cone
- rather small size
- built from ejected lava (cinder-sized fragments)
- steep slope angle
- frequently occur in groups or on other volcanic forms
- rhyolitic (felsic) or andesitic (intermediate)
Composite or stratovolcanic
-most around pacific ring of fire
-large classic shaped volcanoes
-1000s feet high and wide at base
-composed of interbedded lava flows and layers of pyroclastic debris
-rhyolitic to andesitic (VERY explosive)
Ie: mt Shasta, Cali
Fissure eruptions-flood basalts
-Crustal fractures (often intraplate)
-extrudes very fluid basaltic magma (capable of spreading >150 km)
-greatest volumes of lava, called flood basslets
Ie Columbia river basalts
Size comparisons
Shield volcanoes: largest, due to low viscosity basaltic lava spreading fast
Composite-stratovolcanoes: much smaller, steeper, low viscosity lava, explosive!
Cinder cones: v small
Volcanic extrusions
Classified by size, generally referred to as pyroclastic material-“fire fragments”-mafic/felsic volcanoes
<2 mm
-ash and dust: fine glassy fragments (welded tuffs)
-pumice: pros rock from “frothy” lava
2-64 mm
-lapilli walnut-peanut sized
64 mm
-blocks: hardened or cooled lava
-bombs: ejected as hot (incandescent) lava
Volcanic features < 1km in diameter
Crater (major vent)-steep walled summit
Vent-opening to magma chamber
Fumaroles- openings that release just gas
Parasitic cone-built from flank eruptions
Pyroclastic materials- interlayered pyroclastics and lava flows
Volcanic features > 1 km in diameter
Caldera- summit depression, produced by collapse
Pyroclastic flows (or nuee ardentes)
avalanche of hot ash (200c-400c) that moves (about 300 km/hour incinerating all in its path
–many examples; mount Vesuvius (destroyed Pompeii) mt palee 1902(only 2 survivors), and mt unzen
Ash cloud/ash fall
pollution/health hazard
- kills vegetation
- building destruction
- airplane hazards (cloud contains tiny particles or abrasive glsss, sand a rock posing hazard to aircraft engines and structures)
Volcanic hazards
- Pyroclastic flows (or nuee ardentes)
- Ash cloud/ash fall
- Lahars & landslides
- Lava flows
- Poisonous gasses
Lahars & landslides
Lahars: mudflows but with ash
Formed as ice/snow melt and mix with ash/tephra during eruption
-lahars move rapidly (up to 50km/hr
-consistency of wet cement
Lava flows
Felsic flows-uncommon/close to vent
Mafic flows-can be outrun, but not by buildings
Poisonous gasses
9% of magma may be gas
Gasses are expelled as magma rises (p drops) in order of abundance: h2o, co2, so2 (sulfur dioxide)
-so2 reacts with h2o to form aresol sulfuric acid
Ie: lake nyos 1986
-magmatic co2 build up in the lake located in a crater
-gas moved as a heavier-than-air underflow
-killed 1742 & 6k cattle
My St. Helens
May 1980 Washington state
- lateral blast Johnson ridge 6 miles away after landslide on mount st Helen??
- Daniel Johnson and Harry Glick????
Forecasting eruptions
Seismatic activity-magma flow increases seismicity
Heat flow-magma causes volcanoes to “heat up” (measuring temp)
Changes in shape (topographic changes)-magma causes valcanoes to inflate & lava domes: build up of new volcanic structure
Emission increase-changes in gas mix and volume
Geological history-reoccurrence interval or specific volcanoes
Mitigating volcanic hazards
- Danger assessment maps
- Evacuation
- Diverting flowing lava
Danger assessment map
Delineate danger areas showering where -pyroclastic flows -lahars -landslides —used for planning, zoning
Evacuation
Moving high risk area saves lives
-mt st Helen timely evacuation saved hundreds
—sometimes eruptions don’t occur, large expenses
Diverting flowing lava
- explosive
- heavy equipment/walls
- seawater
Volcanic eruptions and climate change
Eject massive amounts of ash and aerosols high in the atmosphere
-enough to block sunlight causing atmospheric cooling
—1815 year without summer due to eruption of tamboro
—1991 eruption of mt pinatubo made 1992 one of the few years NOT one of the hottest on record increase of sulfur dioxide
Deep time
Refers to the immense span of geological time
Understanding time permits us to attach an age to…
Rocks Fossils Geological structures Landscapes Tectonic events
Geological time scale
Eons- largest geological division
Eras-what eons are divided into
Periods-what eras are divided into
*chart on slide 5
Two ways of dating
- Relative
- order of formation or sequence of events
- older versus younger
- principles of geology
- allows scientists to easily unravel complicated geological histories - Numerical (radiometric)
- uses isotopes and radioactive decay to get an absolute time
Geological principles
- Original horizontally (Nicholas steno)
- Superposition (Nicholas steno)
- Lateral continuity
- Cross cutting relationships
- Baked contacts
- Inclusions
- Biotic succession
Principle of Original horizontality
Layers of rock are de
Listed on flat horizontal surfaces, otherwise gravity would cause them to move
Principle of superposition
In an undeformed sequence of layers rocks each bed is older than the one above and younger than the one below. Younger strata are on top; older strata below
Principle of lateral continuity
Strata form laterally (side to side) I’m horizontal sheets. Erosion can cut through one continuous layer
-ie the Grand Canyon
Principle of cross cutting relationships
Younger features cut across older features
- faults, dikes, erosion, etc must be younger than material that is faulted, intruded, or eroded
- an intrusion can’t intrude rocks that aren’t there yet
Principle of inclusions
An inclusion is a rock fragment within another rock
- xenoliths: country rock that fell into magma
- weathering rubble: debris from preexisting rocks
- inclusion is older than the material around it
Principle of baked contacts
Contact metamorphism occurs when country rock is invaded by magma. The protolith of the metamorphosed rock is older. The new metamorphic rocks are probably also older.
Principle of biotic “faunal” succession
Fossil range: first and last appearance, each fossil has a unique range
permit correlation of strata
-locally
-regionally
-globally
*tell us about BIG ecological events (like mass extinctions)
Example sequence of events
- Deposition of horizontal strata below sea level in order 1,2,3,4,5,6,7,8 (oldest to youngest)
- An igneous rock intrudes
- Folding, upLift, and erosion take place
- An igneous pluton cuts older rock
- Faulting cuts the strata and pluton
- A dike intrudes
- Erosion forms the present land surface
Isotopes
Atoms of elements that have varying numbers of neutrons. Have similar but different mass numbers.
Stable isotope: never changes/decays
Radioactive isotope: spontaneously decay
Example:
Carbon-12 not radioactive
Carbon-13 not radioactive
Carbon-14 radioactive
Radioactive decay
Progresses along a decay chain
-decay creates new unstable elements that also decay
-decay proceeds to a stable element endpoint
-temp, pressure, etc do not affect rate
Parent isotope: the isotope that undergoes decay
Daughter isotope: the product of this decay
Half life (t1/2)
Time for 1/2 of all unstable nuclei to decay
-each unstable Isotope has its own diagnostic half life
—after 1 t1/2 1/2 original parent remains
—after 2 t1/2 1/4 of the original parent remains, etc
Types of radioactive emissions/decay
- Alpha decay- emission of a He nucleus
- Beta decay- emission of electron, or neutrino
- Gamma decay- emission of a gamma ray (photon)
As the parent disappears…..
The daughter appears
Typical half lives
Carbon 14: 5730 years
Uranium 234: 245500 years
Cesium 135: 2.3 million years
Rubidium 87: 4.75 billion years
Common isotopes used
The limit of most techniques is about 10 half-lives, beyond that the amount of parent isotope is too small to measure
Effective ranges:
C14: 0-50,000 years (organic)
K-Ar 10^6-10^10 (feldspar crystals)
Rb-sr 10^7-10^10 (rocks)
U-pb 10^7-10^10 (rocks)
Fission track 10^2-10^10 (zircon crystals)
Uncomformities
Represent periods of time when there was erosion or non deposition. Time isn’t missing-rock is!
Three types of unconformities
- Angular unconformity
-James Hutton first to realize enormous time significance of angular unconformities
—mountains created
—mountains completely erased
—new sediments deposited
*a lot of time required - Nonconformity
-metamorphic or igneous rocks overlain by sedimentary strata
—crystalline igneous or metamorphic rocks were exposed by erosion
—sediment was deposited on this eroded surface - Disconformity
-parallel strata bracketing non-deposition
—due to interruption in sedimentation
—May be difficult to recognize
Biosphere
Flow of materials, minerals, and elemental nutrients within the ecosystem
Ecosystem
The organisms, the environment they inhabit and how they interact with each other
-or the biotic and abiotic components of an environment and their interactions with each other
Biosphere 2
September 1991 experiment to try to duplicate an environmental system. Located in Arizona had internal desert, wetland, rainforest, agriculture area, specially mixed soils w microbes, and oceanic area with coral reef and populated with 4000 different organisms
Why did the biosphere two fail
O2 fell and co2 rose to 10x normal amount even though they had calculated how the good web would be created. Why?
-microbes in the soil reproduced and produced prodigious amounts of co2. After two years they emerged hungry and irritable from low o2, with most of the animals involved dying
Energy needed to…
Replace cells, get rid of wastes, re
Reduction, growth, and defense
Photosynthesis formula
6co2+6h2o+solar energy —-> c6h12o6+6o2
Respiration formula
C6h12o6+6o2—> 6co2+6h2o+energy
Limiting nutrients
Nutrients that are so essential that limiting them limits the growth of the organisms
Leibigs law of the minimum
States that the growth of an organism depends on the supply of the nutrient with the shortest supply
-important nutrients include:
—nitrogen and phosphorous (building blocks of dna and rna)
—carbon (abundant but also building blocks of life)
Carbon cycle
Has 7 reservoirs
- Atmosphere (775 tg)
- Surface ocean (600 tg)
- Deep ocean (36,000 tg)
- Lithosphere (75,000,000 tg)
- Fossil fuels (5000 tg)
- Soil (1500 tg)
- Land biota (560 tg)
Nitrogen cycle
Similar to the carbon cycle but differences in reservoir size
- Atmosphere (3.9 billion tg)
- Marine biota (500 tg)
- Ocean (720,000 tg)
- Lithosphere (5 billion tg)
- Soils (140,000 tg)
- Land biota (3,800 tg)
What is nitrogen’s common form
Mostly in inert gas, must be fixed by various soil bacteria plus along with hydrogen to make methane (NH4+) which is used by plants
Phosphorus cycle
Like nitrogen, phosphorus is an essential element in the formation of DNA, RTP, and ATP making phosphorus a “limiting nutrient)
- Ocean (90,000 tg)
- Lithosphere (7,400,000 tg)
- Soil (46,000 tg)
- Minable rock (12,800 tg)
- Land biota (500 tg)
What is phosphorus common in
Mineral apatite and in teeth and bones
Another Important cycle
Potassium (k)
-plant fertilizers today often categorized by their NPK numbers
Geology and biodiversity…. Yellowstone
-Yellowstone park established 1872
-hunting prohibited except for predators, including wolves
-wolves extirpated (local extinction) from park 1926
-scientist visited park in late 1920-1930s noted declining condition of park
-disappearing aspens, beavers (and their dams) among many changes
-elk population increased
-overgrazed bank vegetation
—erosion which put silt into streams and fine sediments can clog fish gills
-without willows beavers fell in numbers, causing:
—fewer beaver dams, more soil erosion
—Silty water and fewer fish hiding places
-wolves reintroduced in 1995
-beaver population went from 1 (2001) to 9 (2011)
Keystone species
A species who’s absence perhaps has a much greater effect down the food chain
Environmental unity
Everything is connected: the air, water, land, people, animals, plant life, everything in our solar system, and all activity may be connected and can affect each other
-ie the wolves in Yellowstone were removed and even the geology of the ecosystem was affected
Biodiversity
The variety of life in the world or in a particular habitat or ecosystem
Measurements:
Richness: number of species
Evenness: how well distributed those species are in the ecosystem
Ecological restoration
The process of assisting the recovery of an ecosystem that’s been degraded, damaged of destroyed. Examples: -returning wolves to Yellowstone -steam restoration -coastal sand dune restoration -flow of water in Florida Everglades
3 big considerations for ecological restoration
- Hydrologic process
- Soil and rock
- Vegetation
To make any consideration we first must….
Understand the processes!
