GEO 104-001 Exam 1 Study Guide (Chapters 1-3)
GEO 104-001 Exam 1 Study Guide (Chapters 1-3) Geo 104-001
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This 17 page Study Guide was uploaded by Jennifer Gintovt on Monday September 19, 2016. The Study Guide belongs to Geo 104-001 at University of Alabama - Tuscaloosa taught by Rona J. Donahoe in Fall 2016. Since its upload, it has received 160 views. For similar materials see Hazardous Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 09/19/16
GEO 104-001 Exam 1 Study Guide Chapter 1: Introduction to Natural Hazards Processes and Natural Hazards • process o physical, chemical, and biological ways in which events affect Earth’s surface • Internal processes o Forces within earth § Ex. Plate tectonics • External processes o Forces on earth’s surface § Ex. Weather patterns, storms related to weather § Driven by energy from the sun Hazzard, disaster, or catastrophe? • Hazard o Any natural process/event that has potential to cause harm to human life/property • Disaster o Occurs over a limited time/in a defined area o Criteria (only one of the three are required) § 10 or more deaths § 100 or more people affected § declared state of emergency § there may be a need for international assistance • Catastrophe o massive disaster o significant damages that require a large sum of money or time to fix Why study natural hazards? • Public knowledge o Helps minimize loss of life and property Biggest killer? 1. Flooding ~9,000/yr 2. Earthquakes 3. Volcanic eruptions Death and damage as a result of Natural Hazards • Effects of hazards can differ • Hazards that have the greatest impact on human life may not have greatest effect on property (and vice versa) o Ex. Disease, famine, drought History and natural hazards: • Repetitive • An area’s history offers clues to the potential hazards that can occur there o Human documentation: Maps, historical accounts, climate and weather data o Natural records: rock types, faults, folds, soil comp. Geologic cycles: • Geo. Conditions govern the type, location, and intensity of natural processes o Tectonic § Large-scale processes that deform earth’s crust and produce landforms § Forces within earth are the cause § Involves the creation/destruction/movement of tectonic plates • Helps explain… o Location of mountains/volcanoes o Distribution of earthquakes o Rock • Igneous • Metamorphic (to change; form) • Sedimentary • Recycling and transformation of earths materials • Linked to all other cycles o Hydrologic § Solar energy drives movement of water between atmosphere and oceans/continents § Processes include • Evaporation, precipitation, transpiration, etc. § Water is stored in compartments such as oceans/atmosphere/rivers/streams/etc. • Reservoirs include- ocean, streams, lakes, ice, groundwater, soil water, atmosphere • Residence time is estimated average time that a drop of water spends in any compartment • o Biogeochemical § Combines three previous cycles § Transfer of chemical elements through a series of reservoirs Fundamental concepts for understanding natural processes as hazards • Science helps predict natural hazards 1. Scientific method § Question-observations®hypothesis (prediction) ® data collection®theory (potentially violated) ® more data collection® law 2. Uniformitarianism § James Hutton-1785 • Present is key to past • The processes that happen today have been happening for years § Human interaction affects geological processes • Present is key to future • Peoples actions today affect future hazards § Environmental unity • One action causes others in a chain of actions and events 3. Prediction vs. forecasting i. Prediction- specific date, time, and magnitude ii. Forecasting- range of probability for event iii. Some hazards can be predicted; most can only be forecasted 1. Identify location of probable event a. Most hazardous areas are mapped b. Ex. Volcanoes/earthquakes occur near plate boundaries 2. Determine probability of event 3. Observe precursor events • Risk analysis b. Risk= (probability of event) x (consequences) c. Consequences= damages to people, property, economics d. Acceptable risk i. The amount of risk that an individual or society is willing to take e. Can’t always assess the probability of the event or the magnitude of the consequences • Linkages f. Hazards linked to each other (Environmental Unity) i. Some events can cause others 1. Ex. Earthquakes ® landslides g. Physical environment is linked to hazards i. Volcanic eruptions ® global warming • Humans can cause disasters into catastrophes • Consequences can be minimized a. Effects: i. Direct- flood waters carry homes away ii. Indirect- psychological effects b. Minimizing impact of disaster i. Recovery 1. Declaration of state of emergency 2. Restoration- power, water, basic functions 3. Reconstruction- back to where we were before the event Chapter 2: Internal Structure of Earth and Plate Tectonics Earths Structure: • Layers are different o By composition/density § Mafic • Low in silica, high iron and magnesium, dark in color, high density (ferromagnesian) § Silicic (felsic) • High silica, low iron and magnesium, lighter in color, low density (non-ferromagnesian) o By physical properties (solid/liquid) o Components § Inner core • Solid • High temperature • About 90% iron • High density § Outer core • Liquid • Composition similar to inner core • Less dense than inner core § Mantle • Solid • Largest volume of any layer • Composed of iron/ultramafic rocks § Crust • Outer rock layer of earth • Low density • Moho discontinuity o Separates lighter crustal rocks from more dense mantle § Lithosphere • Strong and rigid • Compromised of the crust and the outer mantle § Asthenosphere • Underlies the lithosphere • Weak and plastic • Capable of slow flow Continents v. Ocean basins • Continental crust o Thick o Old o Light density • Oceanic crust o Thin o Young o Heavy density How do we know so much about earth’s interior? • Seismology o The study of earthquakes o Earthquakes cause seismic energy to move through earth § Some waves move through solids but not liquids § Waves can be reflected or refracted (change in path) o Wave movement helps us identify Earths internal structure • Magma is created in asthenosphere o Slabs of lithosphere that have sunk deep into the mantle exist Plate Tectonics: • Continental Drift- Alfred Wegener (1913) o Africa and South America “fit together” o Restricted plant & animal fossils found on widely separated land masses o Ancient glacial deposits on southern continents § Hypothesis abandoned for lack of plausible driving mechanism for movement of the continents Plate Tectonics II: • Exploration of sea floor (1950s) o Glomar Challenger- sonar used to map topography of sea floor (bathymetry) § Discovered ocean ridges and deep sea trenches • Theory or Seafloor Spreading- Harry Hess (1962) o New ocean crust created at oceanic ridges o Crust moves laterally from ridge to trench o Ocean crust is destroyed at oceanic trenches o Validity of seafloor spreading established by § Identification and mapping of oceanic ridges § Dating of volcanic rocks on the ocean floor • Youngest rocks found at ridges • Oldest rocks found at edges of ocean basins • Ocean sediment thickness increases away from ridge § Mapping of earthquake focal depths near deep ocean trenches (Benioff Zones) § Understanding and mapping of paleomagnetic history of ocean basins Paleomagnetism: • Study of rock remnant magnetism • Earth’s magnetic field can be represented by a dipole o Force lines extend from North Pole to South Pole o Caused by convection in outer core and Earth’s rotation • Igneous rocks that have minerals containing iron preserve the orientation of the Earth’s magnetic field when cooled below the Curie Point o Time at which an iron-rich mineral “locks-in” the Earth’s magnetic field • Magnetic reversals are cyclic but random o Occur on average every few 100,000 years o Change in polarity takes place over a few 1000 years • Magnetic reversals help to date Earth’s rocks History of Plate Tectonics III: • Magnetic mapping of ocean floor (early 19600s) o Magnetometers- instrumentals that measure magnetic properties of rocks • Magnetic anomalies on seafloor discovered- Vine & Matthews Theory (1963) o Noticed that the ocean floor had stripes when mapped § Areas of “normal” and “reversed” magnetic fields o Stripes were parallel to oceanic ridges Seafloor Age: • Geologists can infer ages for the ocean rocks using magnetic anomalies • Seafloor is no older than 200 million years o But there has been ocean crust found in the Mediterranean that may be as old as 340 million-years old • Spreading at the mid-ocean ridges can explain stripe patterns • Rising magma at ridge is extruded o Cooling rocks are normally magnetized o Field is reversed with new rocks that push old rocks away Plate Tectonics: • Large scale geological processes that deform Earth’s lithosphere • Produce landforms • Processes are driven by forces that occur within the Earth (internal energy) • Earth’s lithosphere is broken into plates o 7 major plates § N. American § S. American § Pacific § Eurasian § African § Indo-Australian § Antarctic • lithosphere is created at ridges and destroyed at subduction zones • Triple plate boundary- where three plates come together- higher rates of strain Locations of earthquakes/volcanoes define plate boundaries • Plate boundaries are defined by areas of seismic activity • Earthquakes/volcanoes are associated with plate boundaries Seafloor spreading and plate tectonics: • At oceanic ridges new crust is added to edges of divergent lithospheric plates o Continents are carried along with moving plates • Lithosphere is destroyed along convergent plate boundaries (subduction zones) Subduction plates generate e-quakes and magma: • Subducting ocean plates are cold+ brittle o Carry wet sediment down with them • E-quakes occur along the path of the descending plate • Plates and sediment come in contact with hot asthenosphere • Wet sediments melt first to generate magma; eventually the basaltic plate will begin to melt • Magma rises to produce either plutons or volcanic activity Convection: • Earth’s internal heat causes mantle to heat up and become less dense • Less dense mantle rises • Mantle moves laterally, cools and falls back downward • Like convection of water boiling in pan Convergent boundaries: • Ocean-continental o Ocean plate subducts under continental plate • Continental-continental o Two continents approaching each other o Because both plates are buoyant, neither one wants to subduct under the other o Continents essentially merge and create massive earthquakes • ocean-ocean o convergent boundary forms between plates of oceanic lithosphere o older, thicker, and denser plate subducts Divergent boundaries: • two plates separating from each other • generally oceanic, but can be continental Transform boundaries: • ocean-ocean or continent-continent • this is where two plates slide past one another • earthquakes are common along transform boundaries Hot Spots: • volcanic centers resulting from hot materials from deep in the mantle • hot material moves up through mantle and overlying plates (believed to come up from core-mantle boundary) o found under both oceanic and continental crust o ex. Yellowstone National Park • plates move over hot spots, creating a chain of island volcanoes o seamounts = submarine volcanoes o ex. Hawaiian-Emperor Chain Plate tectonics, continental shape + Mountain ranges: • movement of tectonic plates is responsible for the present shapes/locations of continents • Pangea o break-up of Pangea produced: § Laurasia (Northern hemisphere) Gondwana (Southern hemisphere) Plate tectonics helps solve geologic problems: • Reconstruction of Pangea and recent continental drift clears up o Fossil data difficult to explain with separated continents o Evidence of glaciation on several continents o Geologic “coincidences” on either side of the Atlantic Ocean § Rock types and ages shortened mountain belts that span two continents Driving mechanism: • 2 possible driving mechanisms to explain plate tectonics o ridge push § gravitational push away from crest of mid-ocean ridges o slab pull § occurs when cool, dense ocean plates sink into the hotter, less dense asthenosphere • weight of descending slab pulls the plate along • evidence suggests that slab pull is the more important process of the two Chapter 3: Earthquakes Earthquake Catastrophe: • Kill a large number of people/cause extensive damage in seconds o 850,000 killed in 16 century Chinese earthquake • Contrasting examples: o 2010 Haitian 7 M § killed 316,000 o 1994 Northridge CA 6.9 § killed 60 o Most deaths are “human induced” due to poor building construction § Lack of earthquake construction codes § Disregard for existing codes due to corruption Earthquake Terms: • Focus o Point along a fault plane where rock rupture starts o May not always see surface rupture • Epicenter o Geographic location of the place directly above the earthquake focus Haiti: • 7.0 M • death tolls linked to poor construction methods Northern California, Loma Prieta: • 7.1 M • killed 63 • injured 4,000 Earthquakes: • Many earthquakes in any given day o The majority are too small to be noticed • Earthquakes are compared based on… o Magnitude § Amount of energy released; measuring the amount of shaking that occurs o Intensity § The effects on people and structures • Magnitude o Measured on a logarithmic scale o Moment Magnitude- Depends on: § Area of rupture along fault § Amount of movement along fault (slippage) § Rigidity of the rocks at the point of failure § Used by seismologists today o Richter Magnitude § Developed for Southern Cali. - Charles Richter § Mostly used by the media o Ground shaking increases by 10x for each magnitude unit o Energy released increases by 32x with each magnitude unit o Ground motion (seismic wave amplitude) is measured by a seismograph Earthquake Intensity: • Modified Mercalli Scale- measures earthquake intensity o Qualitative scale (1-12) based on damage to structures and people’s perceptions of shaking o Intensity depends on: § Distance from the epicenter § Depth of focus (point of rock failure) and the slip direction (how much movement occurs along the area of the fault plane) § The type of rock in the area (consolidated, unconsolidated, (sediment) fluid) o Modified Mercalli Intensity Maps show where the damage is most severe Shake Maps: • Use seismographic data and human accounts to show areas of most intense shaking Earthquake Processes: • Distributed along faults o Places where rocks are broken and displaced o All plate boundaries are faults • 2 basic faults: o Strike Slip o Dip Slip • Long-term rate of movement is the Slip Rate o Measured in mm/yr. or m/100yr. • Sudden rupture of rock produces seismic waves o Release of stored energy o Elastic rebound theory § When a fault undergoes strain, it accumulates energy and slowly begins to deform § Once internal strength limit is reached, seismic waves are released Stress/strain: • Rock deforms (shows strain) under stress • Increasing stress can cause… o Elastic deformation (reversible) o Plastic deformation (permanent) o Rupture § Occurs when rocks strength is exceeded Types of stress: • Compressional Stress o Squeezing stress o Convergent boundaries (COMpressional…CONvergent) • Tensional Stress o Pulling apart stress o Divergent boundaries • Shear Stress o Horizontal motion o Transform boundaries § EX. San Andreas Fault- Cali. Fault Types • Strike-slip (transform) o Crust moves in horizontal direction § Right lateral strike-slip § Left lateral strike-slip • Dip-slip o Vertical movement o Includes two walls defined by miners as § Footwall: where miners put their feet § Hanging wall: where they hang their lanterns o Named by which direction (up or down) the hanging-wall moves relative to the footwall • Normal: o Hanging wall moves down relative to footwall (think normal movement of gravity) o Pull apart (divergent) • Reverse fault o Hanging wall moves up relative to footwall o If angle is 45 degrees or less, it is a thrust fault • Blind faults do not extend to surface Fault Activity: • Active fault o Moved during the past 10,000 years of the Holocene Epoch • Potentially Active Fault o Moved during the Pleistocene (10,000-2 million years) but not the Holocene Epoch • Inactive faults o Faults that haven’t moved during the past 2 million years Tectonic Creep/Slow Earthquakes • Tectonic Creep o Occurs when movement is so gradual that earthquakes are not felt § Can produce slow earthquakes § Also called fault creep • Ex. Hayward fault (along San Andreas fault) o Can slowly damage roads, sidewalks, and building foundations o Can last from days-months o Slow earthquakes can have magnitudes between 6-7 § Large areas of rupture, but small displacements Seismic Waves: • Body waves o Caused by release of energy from rupture of a fault o Travel through the body (interior) of the earth o P waves § Primary/compressional waves • Move fast w/ push/pull motion • Move through solid, liquid, and gas • Is possible to hear them o S waves § Secondary/shear waves • Move slower with up/down motion • Only travel through solids • Surface Waves o Move along Earth’s surface o Pass through everything o travel slower than body waves o move vertically and horizontally with rolling motion o responsible for most of the damage near the epicenter o Love Wave § Horizontal ground shaking o Rayleigh Wave § Wave-like rolling ground motion § Knock people off their feet Earthquake shaking: • Shaking experience depends on o Magnitude § Shaking increases w/ magnitude o Location in relation to epicenter, depth of focus and direction of rupture § Determined from earthquake seismogram records § Shaking usually decreases with distance from the epicenter and increasing depth of focus o Local soil and rock conditions § Unconsolidated (loose sediment) and wet materials amplify seismic waves (liquefaction) § Certain geologic structures can focus seismic waves • Ex. Graben, Syncline Local geologic conditions: • Different materials respond differently to an earthquake o Seismic waves move faster through consolidated material (bedrock) o Move slower through unconsolidated sediment and soil o Move slowest through unconsolidated materials with high water content • Material Amplification o Energy is transferred to the vertical motion of the surface waves The Earthquake cycle: • Elastic strain drops after an earthquake + reaccumulates before the next event • The earthquake cycle consists of four (five) stages o 1: period of inactivity along a segment of fault o 2: period of small earthquakes produced by accumulated elastic strain o 3: Foreshocks may occur hours to days prior to a major release of stress o 4: Mainshock o 5: Aftershock Foreshocks: • small earthquakes before the major event are called foreshocks (days/months leading up to main event Aftershocks: • adjustments after a major earthquake can generate small quakes called aftershocks Plate boundary earthquakes: • Subduction zones o Site of world’s great earthquakes (megathrust earthquakes) § Ex. 9.0 japan earthquake in 2011 § Ex. Cascade mountains (continental and oceanic plate convergence) § Ex. Aleutian Islands (convergence between two oceanic plates) • Transform Fault Boundaries o San Andreas Fault in California (Between N. American and Pacific Plates) § Ex. 1989 Loma Prieta, 1994 Northridge earthquake Intraplate Earthquakes • Earthquakes that occur within plates = rare, but can be large and extremely damaging • New Madrid Seismic Zone o South of St. Louis, MO o 1811-1812 2 earthquakes with M 7.5+ felt from New Orleans to Quebec City, rang church bells in Boston • Charleston, S.C. o 1889 Earthquake was felt from Canada to Cuba (M ~7.3) and as far west as Arkansas Primary effects of earthquakes: • ground rupture o displacement along the fault causes surface cracks § horizontal displacement (especially common along a transform fault) § vertical displacement (produces fault scarp) • cliff created from vertical displacement • Shaking o causes damage to buildings, bridges, damn, tunnels, pipelines, etc. § measured as ground acceleration § buildings may be damaged due to resonance • matching of vibrational frequencies between ground and building Secondary effects of earthquakes: • liquefaction o near-surface layer of water-saturated sand chances rapidly from solid to liquid o “quick sand” o can produce “sand blows” o after shaking stops, ground re-compacts and becomes solid o things that are buried in the ground can also rise to the surface • Elevation changes o Regional uplift and subsidence • Landslides o Earthquakes= most common trigger, especially in mountainous areas o Loss of human life can be substantial • Tsunamis o Earthquake induced tidal wave • Fires • Disease o Caused by loss of sanitation/housing, contaminated water supplies, disruption of public health services, and the disturbance of natural environment § Northridge – 1994 earthquake- caused “Valley Fever” • Traced back to the inhalation of fungal spores Human interaction with earthquakes: • Reservoir-induced seismicity o Weight from water reservoirs may create new faults or lubricate old ones • Deep Well disposal o Liquid waste disposal deep in the earth can increase fluid pressure on faults • Nuclear explosions o Can cause the release of stress along existing faults § Proposed as an earthquake control method… Can earthquakes be predicted? • Parkfield, CA experiment o Moderate earthquakes have occurred at regular intervals in area since 1857 § Approx. every 22 years o 1985- predicted that next event would happen by 1993 o finally occurred on Sept. 28, 2004 o so…not really Minimizing Earthquake hazard • focus of hazard minimization is on forecasting and warning • National Earthquake Hazard Reduction Program goals (USGS) o Know where the earthquake may originate (know information about faults, etc.) o determine earthquake potential o predict effects of earthquakes o apply research results with public education on hazards/planning Estimating seismic risk • hazard maps show earthquake risk • show either o locations and magnitudes of historic events o probability of a particular event o amount of shaking Short term prediction • Prediction o Gives timeframe and location of a certain magnitude event o Relies on precursors § Events/changes that occur before the earthquake mainshock o Pattern and frequency of earthquakes § Foreshocks, microearthquake swarms o Deformation of ground surface § Changes in land elevation and tilt o Seismic gaps along faults § Areas that have not experienced recent earthquakes o Geophysical and geochemical changes § Changes in Earth’s magnetic field, gravity, conductivity, groundwater levels, temperature & chemistry o Animal behavior can be a precursor event Earthquake warnings: • Plan for issuing an earthquake prediction or warning developed by USGS 30 years ago • Warning systems are technically feasible o Earthquakes can produce radio waves- Radio wave system (Japan) o Seismometer/transmitter system (Southern California) Community preparations for earthquake hazards • Location of critical facilities o Hospitals, schools, police, fire, etc. must be located in earthquake safe zones o Need for details maps of ground response (microorganizaton) • Structural protection o Buildings, bridges, pipelines, etc. need to be designed to withstand the vibrations created by an earthquake o Retrofitting of older buildings may be necessary o Costs must me balanced with risk to human life • Education • Increased insurance and relief measures Self-Check Multiple choice: 1. Which of the following is not a characteristic of mafic material? a. high silica b. high iron/magnesium c. high density d. dark in color 2. The inner core is… a. liquid b. the outer rock layer of Earth c. solid d. low in density 3. Magnetic reversals… a. occur daily b. tell us when the next earthquake will occur c. are no longer studied d. are cyclic but random 4. The two basic faults are a. strike-slip b. fault scarp c. dip-slip d. both a and c 5. Earthquakes can cause all of the following except a. liquefaction b. gaping faults c. shaking d. ground rupture 6. The deadliest natural disaster is a. earthquakes b. flooding c. volcanic eruptions d. tsunamis True/False 1. Magnetic reversals help date Earths rocks a. T b. F 2. Plate boundaries are not defined by areas of seismic activity a. T b. F 3. All plate boundaries are faults a. T b. F 4. The history of an area can offer clues to potential hazards that can occur there a. T b. F 5. The hydrologic cycle is when wind energy drives movement of water between atmosphere and oceans/continents a. T b. F 6. Earthquakes can easily be predicted a. T b. F Matching: 1. _____ Acceptable risk A. Gravitational push away from crest of mid-ocean ridges 2. _____ Seafloor Spreading B. Geographic location of the place directly above the earthquake focus 3. _____ Plate Tectonics C. Earth’s internal heat causes mantle to heat up and become less dense. The less 4. _____ Seismology dense mantle rises, then moves laterally, cools and falls back downward 5. _____ Convection D. Point along a fault plane where rock rupture starts 6. _____ Continental Drift E. Proposed by Harry Hess and explained that new ocean crust is created at oceanic 7. _____ Ridge Push ridges, which then moves laterally from ridge to trench and is then destroyed at 8. _____ Focus oceanic trenches F. The amount of risk that an individual or 9. _____ Slab Pull society is willing to take G. Large scale geological processes that 10. _____ Epicenter deform Earth’s lithosphere H. The study of earthquakes I. Proposed by Alfred Wegner and explained why Africa and South America “fit together”, restricted plant & animal fossils were found on widely separated land masses, and ancient glacial deposits were found on southern continents J. Occurs when cool, dense ocean plates sink into the hotter, less dense asthenosphere
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