GEOL 106 notes.docx

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Department
Geological Sciences and Geological Engineering
Course
GEOL 106
Professor
John Hanes
Semester
Winter

Description
Introduction 1/8/2013 12:41:00 PM Civilization exists by geologic consent, subject to change without notice.  Will Durant, historian Nature can jump up and hit us in the face  Volcanic eruptions  Hurricanes  Cyclones  Flooding  Drought  Earthquakes  Tsunamis Population growth has caused an increase in death from natural disasters Humans can jump up and hit nature in the face  The story of the Aral Sea How do we manage the risks that these natural and anthropogenic hazards pose? Head TA- Tyler Nash [email protected] Midterm notes Step 1- carry out studies to understand the hazard Step 2- determine the risk from that hazard in the particular region of interest Step 3- determine ways that you could reduce the risk Step 4- do a cost-benefit analysis to determine what mitigation techniques your society can “afford” to do Step 5- implement mitigation techniques to the extent determined (warranted) by your cost-benefit analysis 3 main factors that control how severe an excursion into the hazard zone is  Intensity  Duration  Rate of Change After effects of earthquake  Tsunami  Ground failure  Fires  Disease Earth-System Science and Earth-System Management/Engineering 1/8/2013 12:41:00 PM 1969  landed on the moon  huge increase in number of USA laws on environmental protection  “The world changes as we learn to see it in new ways. And the way we see the world depends on how we use it”- David Ruthenberg  “We made all this way to the Moon to finally discover Earth”- William A. Anders View of Earth from space led to increased awareness of the fragility of the Earth and the need to better understand it.  The President of the USA commissioned a study to the Earth System- What do we need to know in order to live in concert with this fragile Earth?  National Research Council o The goal of the solid-earth sciences is:  Understand the past, present, and future behaviour of the whole earth system  Use this understanding to maintain an environment to which the biosphere and humankind will continue to flourish  Objectives associated with this goal:  Understand the process involved in the global earth system with particular attention to the linkages and interactions between its parts (the geospheres)  Sustain sufficient supplies of natural resources  Mitigate geological hazards  Minimize and adjust to the effects of global and environmental change Earth System Science= set of interacting subsystems  Practitioners see to understand how its parts and their interactions evolved, how they function today and how they may be expected to function in both the near and distant future Five “reservoirs” of Earth System  Atmosphere  Hydrosphere  Solid Earth  Life  Stars and planets (tides, sunlight…) “The Earth, as it now exists, is a human artifact. It reflects the (frequently unintendedand unconscious, but nonetheless real) design of a single species.”- Brad Allenby Earth-systems engineering= managing earth systems  The earth is increasingly a product of human engineering o Even during the roman empire, lead contamination began to rise, with a sharp increase when we began using oil How does past earth systems engineering compare to future?  Scale- in past, was more local/ less global  Intent- in past, regional/ global effects were unintended and unanticipated Thomas Midgely  In 1921, Midglet found that tetra-ethyl lead reduced engine knocking (invented lead gasoline)  In 1930-31, he invented CFCs (get up in the atmosphere and break up the ozone)  He “had more impact on the atmosphere than any other single organism in Earth history” Dramatic increase in coal, metal, numbers of species lost each year and earth moved by humans at industrial revolution. World-wide total consumption of resources: 60 * 10^9 tonnes/year Total mass of sediment transported to the sea: 16 * 10^9 tonnes/year  Humans move 4 times as much as other natural processes  BUT we can’t produce and use Earth materials without generating waste so our waste production has also increased exponentially Why has there been such a dramatic increase in the impact of humans on the earth system?  Population growth o Currently growing by 74 million people per year  Advances in technological capabilities Engineering the Climate  Seeding hurricanes with dust may reduce its force Think globally, act locally  Everything you manage has an impact Read pg. 2-11, 19-27 The question: “To what end are human engineering, or should human engineer, the Earth?”- Allenby  It’s a moral one, not a technical one  We can do it, but should we? And if yes, to what extent? Towards what end? “The issue, then, is not whether we should begin Earth-system engineering, because we have been doing it for a long time, albeit unintentionally. The issue is whether we will assume the ethical responsibility, to do ESE rationally and responsibility.” - Allenby In earth systems, there is an ethical dimension- you need to define your desired endpoints (i.e. you need to know where you are going)  Is the ultimate endpoint sustainability? Sustainable development: development that meets the needs of the present without compromising the ability of future generations to meet their own needs (World Commission on Environment and Development; 1987) Is sustainability enough? Martini Glass World  UN Development Programme, “The wealth of the world’s 300 wealthiest individuals is equal to the combined annual incomes of 41% of the human population” What is a suitable ethical framework for earth-systems engineering?  Sustainability  Equity Managing the Earth requires:  A technical dimension  An ethical dimension  An economic dimension  An environmental dimension o All 4 combined is (environmental) risk management o What risks are we willing to take for what benefits  “The proper role of government in capitalistic societies in an era of man-made brain power industries is to represent the interest of the future to the present” - Lester Thurow “ Where should we spend whose money to undertake what programmes to save which lives with what probability” Risk Analysis and Risk Management 1/8/2013 12:41:00 PM How to mitigate a (geological) hazard- minimize damage and loss of life/injuries  Similar approach used for all types of risks Scenario: the government of Ontario proposes to build a nuclear reactor on the shore of Lake Ontario near Kingston Our task: carry out a risk analysis and risk management study for the government, focused on seismic risk Hazard: something which may cause harm to people (death/injury/property damage) There are landslides on Mars- is there a hazard from Martian landslides? Yes! We have human property on Mars. A) Natural hazards B) Anthropogenic hazards (human-induced)  A and B are often intertwined Resource: something that is useful to us  Water- drinking water, hydroelectricity (resource) OR flooding, ice storm (hazard)  Damage threshold: when a resource becomes a hazard How do you decide what the damage threshold is?  Partly by empirical observations and scientific studies  Ultimately by societal “preferences” (i.e. choices) o Consider pollution. Pollution= hazard. The very notion of pollution is culturally dependent. We define what is or is not pollution.  Over time, there may be changes in human tolerance/sensitivity to the hazard Synergy  Snow (within threshold) + wind (within threshold) = blizzard (hazard)  Each on its own might be a resource an no problem, but together produce a hazard What are 3 main factors that control how severe the hazard “event” is?  Absolute amount (intensity) o Way too much or too little  Rate of change o Too fast- not enough time to adjust to the change o E.g. sudden impact of a large meteorite can lead to mass extinction o E.g. burning, by humans, of oil, coal and gas causing increase in CO2 in the atmosphere may be leading to enhanced global warming  Duration of event o Too long After a hazard event there are both losses and gains  Public health- accidents, obesity rates, alcohol consumption and CHD decreases after hazard  Haitian earthquake may have left clues to petroleum reservoirs that could aid economic recovery When does a hazard event become a disaster or catastrophe?  Number of people affected- loss of life, injuries  Economic loss  Media coverage- societal reaction  Recovery time  Geographic scale- size of region  Preventability  Why is the distinction important? o Government/world aid o Historical perspective- how often do really big events happen? Truism in disasters  “the poor lose their lives while the rich lose their money”  90% of deaths are in the less industrialized countries  75% of economic damage is in the more industrialized countries Risk= the probability of the hazard occurring (Ph) * the severity of the consequences if the hazard happens (Sh)  Risk of bumping toe o ½ * 1 = ½  Risk of serious injury in an automobile accident o 1/100 000 * 1 000 000 = 10 000  How do we measure the probability of the hazard occurring and the severity of the consequences if the hazard happens? o Empirical observations and scientific studies o Social/economic impact studies How much risk are we willing to incur? empirical observations and scientific studies social/economic impact studies Should you believe the experts -wise to add a margin of safety in risk analysis concept of safety factor (probability of failure) experts have probably already added that margin of safety how much risk are we willing to incur -once you have the data (the determined values of Ph and Sh), you make your choice -it is entirely a matter of personal/societal choice -risk- cost benefit analysis- fish ride Cost benefit analysis- economic+environmental+social+personal choice -what risks are we willing to take for the benefits A CRAVING FOR EXOTIC -Toronto wants more diverse street food but puts up obstacles for health and safety -in rural areas health and safety threaten choices- to protect from food risk- example of risk -important to manage child’s risk- things can be gained by taking a risk PEOPLES PERCEPTION OF RISK -tending to increase risk perception Involuntary hazard Direct impact (earthquake) Dreaded hazard (cancer) Many fatalities per event (air fatalities)  tending to decrease risk perception Voluntary hazard Indirect impact (drought) Common hazard (road accident) WORTH OF A LIFE  To whom is the life important individual person o Relatives o Company looking at employees o Government o Society as a whole A persons worth in society Young vs old educated vs not educated present value vs future value rich vs poor Value of statistic of life, placed at $8.16 millionVSL , is VSLY a better measure Hazard is what we are going to look at the risk from RISK ANALYSIS  understand the hazard (in general)  determine the risk from the hazard for the region of interest (risk=PhxSh) RISK MANAGEMENT  determine ways to reduce Ph and/or Sh  cost benefit analysisdetermines what you can afford to do  implement mitigation techniques if warranted Earthquakes 1/8/2013 12:41:00 PM The first step in a risk analysis of a natural hazard: Understand the hazard What causes earthquakes? Where do earthquakes occur? What energy do the Y release? What exactly causes damage? Movement along faults causes earthquakes San Andreas fault Elastic rebound theory The rigid part of the Earth can store elastic energy- when it breaks the elastic energy is released Earthquakes happen when either a fault forms or there is an episode of movement on a pre-existing fault. In both cases, stored energy is released. Fault: a break/crack in rocks along which there has been appreciable displacement For a big earthquake fault motion need to be only a meter or so Strike-slip faults- horizontal motion, look for offset streams Reverse dip-slip faults- sub-vertical or vertical movement, results in a fault scrap, energy pushes land together Normal dip-slip fault- “down the ramp”, energy pulls land apart Large earthquakes can be associated with any of the 3 fault types but the biggest are associated with reverse dip slip faults Rivers are often found to occupy faults/ fault zones (because the broken up rocks can be more easily washed away) We often build major dams on such rivers because the rivers make canyons Focus: the “point” source of energy release on the fault Epicenter: the point at the Earth’s surface that is directly above the focus, where the damage will be the greatest because it is the closest place at Earth’s surface to the focus Understanding the hazard What causes earthquakes? Motion on faults. Where do earthquakes occur? Use seismometers What energy do they release? Use seismometer Seismometers allow us to  Detect the energy from a quake  Measure distance to an quake and thus locate it  Measure the energy released during a quake How do they do this?  Pencil hanging over paper (first one in 1889) Best to have 3 seismometers: 2 horizontal (east and north) and 1 vertical How do we find the focus of an earthquake? In other words, how far away is he earthquake? First we need to know what seismic waves are, and how they behave. Surface waves  Love waves (horizontal motion), Rayleigh waves (circular motion)  Surface waves generally cause the most damage at surface Seismic Waves Seismic waves radiate out from the focus of an earthquake as body waves Body waves  Turn into surface wave when they reach the surface of the Earth  Two kinds: o P-waves: push-pull (compression-rarefaction), primary o S-waves: shear, secondary  The velocity of P- and S-waves depends of elasticity divided by density of the material they are passing through  In other words, the more elastic a material is, the higher the seismic velocity  The more dense a material is, the lower the seismic velocity  So, both P- and S- wave velocities change when they move into a different material  P waves travel faster than S waves  First comes P, then S, then surface Vp= √ K+ 4/3 M over p (P-wave) Vs= √M over p (S-wave) P=density K and M= elastic moduli Measure of elasticity: K= compressibility modulus Stress needed to compress the material M= shear modulus Stress needed to change shape Seismic Velocities for Rocks at Earth’s Surface P-waves =5.6 km/sec S-waves =3.3 km/sec So finally, to measure distance to an earthquake focus, we use travel times- the time between the P and S wave arrivals at your seismometer For earthquakes: since we didn’t know seismic velocities at depth, we needed to first create an empirical travel-time graph For earthquake of known location and time, obtain the P-S arrival-time differences from seismometers around the world At what depth do earthquakes occur at?  At less than 700km depth (ie. In the outer 10% of the Earth)  And 90% of earthquake foci are at depths less than 100km Why do earthquakes occur in the outer 10%?  Only the outer part of the Earth is rigid enough (ie. Sufficiently elastic) to experience brittle failure (fault formation)  Deeper in the Earth it is too plastic How do we estimate energy released from an earthquake?  Measure the intensity based on observable damage e.g. Mercalli Scale o Subjective, varies with distance from epicenter Earthquakes: How do we estimate the energy released by an earthquake?  Measure the intensity  Measure the Richter magnitude o A quantitative measure of energy released- determined from the maximum S-wave amplitude on a seismogram (corrected for distance) o Each integer on the scale represents an amplitude difference of 10 (mag2 is 10 times bigger than mag1) ie it is a logarithmic scale o It is an open-ended scale (we don’t know how high it could go) o Each magnitude integer step corresponds to approximately a 30-fold difference in energy release o How much more energy is released in a magnitude 7 earthquake than in a magnitude 5 earthquake? 30 times 30=900  How about magnitude 8 earthquake? 30 times 30 times 30= 27,000 o The largest earthquake ever recorded are 9 on the Richter scale o Earthquakes less than 2.5 magnitude are not felt by humans o What do the Richter numbers mean in terms of actually energy released? How frequent are Earthquakes?   “BIG” Earthquakes rarely happen  Power law relationships- on a log-log plot, you get a straight line Less than 3 100,000 per year Greater than 3 30,000 per year Greater than 6 100 per year Greater than 7 20 per year What exactly causes damage?  Determine this by o Empirical observations o Laboratory experiments o Computer modeling  The closer you are to the earthquake, the greater the damage  The greater the magnitude, the greater the damage  BUT this is modified by natural and anthropogenic conditions o Natural: nature or soil/rocks o Anthropogenic: nature or the structures that we build  List of earthquake hazards o Surface faulting- structures on the fault will be disrupted by the tearing motion  So don’t build right on active faults o Ground shaking- this is generally the greatest threat to buildings and people  The most damage from ground shaking is generally a direct consequence of surface wave motion  And, if you are close to the epicenter, the P and S wave arrivals  The amount of shaking also depends on the nature of the soil/rocks in the area  Soft soils (clay) shake more than stiff soils (sand) which shake more than rock o Material amplification effect  When seismic waves slow down as they go into another material  Some energy is transferred into greater shaking  Rock- least shaking, sand soil- intermediate shaking, clay soil- most shaking  The most severe shaking is in water, saturated clay soil o After shocks  Smaller earthquakes that occur soon after the main shock, with epicenters in the same area as the main shock  Soon? Minutes to a year after Earthquake hazards  Surface faulting  Ground shaking  Ground failure  Tsunami o Causes  Seafloor earthquakes  Underwater landslide  Collapse of the flank of a volcano into the sea  Submarine volcanic explosion  Impact of meteorite into the ocean o Tsunami in Lake Ontario? Probably not. Maximum height of 2 meters.  Because of shallow depth of Lake Ontario  Amount of water displaced by fault movement is small  Speed of tsunami wave is slow  BUT! A big lake tsunami can happen if it is triggered by a major landslide. Fortunately there are no high mountains near lake Ontario.  Fires o E.g. the 1906 “fire” in San Francisco  Disruption of water supplies  Disease o Cholera epidemic Haiti 2010 (unclean water)  Human-induced seismic hazards o A) Dam construction Reservoir Dam
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