Geology 106 notes.doc

22 Pages

Geological Sciences and Geological Engineering
Course Code
GEOL 106
David Alan Hanes

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Geology 106 Week 2- Lecture 1 I. Do readings from textbook: chapter 1; pages 2-11; pages 19-27 Earth-system science, management and engineering: • In managing earth system there is an ethical dimension --> you need to define your desired endpoints (i.e, you need to know where you’re going) --> is the ultimate endpoint sustainability ? • What are the desired endpoints? Is it sustainable -sustainability is not enough Sustainability and Equity • What is a suitable ethical framework for earth systems engineering? Minimizing the RISK and scale of unplanned or undesirable perturbations in such systems is an obvious earth system engineering objective Risk Analysis and Risk Management: • How to mitigate HAZARDS • we carry this out in order to minimize damage from hazards, disasters and catastrophes --> First example in the course: Earthquakes - In the last 2 years the world has suffered some of the biggest earthquakes with some of the largest causalities of the last 800 years - The earthquake with the most causalities of the last 800 years was in China with over 800,000 deaths Definition of HAZARD: • - something which might cause harm to people (death, injury, property damage etc.); example could be: avalanche, landslide etc. There are landslides on mars. • Is there a Hazard from Martian Landslides even though there are no humans? - there is a hazard because although there are no humans, there is human property on mars that costs millions of dollars Definition of “Natural Hazards”: • Anthropogenic hazards (human induced) Distinction between Hazard and Resource • Resource: something that is useful to us • Hazard: something which may cause harm to us Examples: • Water as a hazard - not having enough could equate to drought - having to much could cause a flood or tsunami Water as a resource: - necessary for human survival - growing food/crops • Sewer Gas as a resource/remedy: - important role in regulating blood pressure - relaxes blood vessels - biological importance in hypertension Geology 106 Sewer Gas as a hazard? ... Hazard vs. Resource • how do you decide what the damage threshold is? - partly by empirical observations and scientific studies - ultimately by societal “performances” (i.e, human choices) consider things like pollution; pollution = hazard • - we define what is or is not pollution (i.e, hazard) Note: over time, there may be changes in human tolerance/sensitivity to the hazard Example: - Wind in Kingston as resource; wind turbines were built so wind was converted to resource - Wind as hazard: when there is snow on top of windy conditions in Kingston, that causes potential blizzards Week 2 - Lecture 2 • Imagine there is a location with a fixed human population and infrastructure (e.g. Kingston - imagine that we experience a hazard “event” (i.e, go past the damage threshold); ex. a flood event Three factors that control/determine how serve the “hazard event” are: 1) Length of time (duration of the event) 2) Intensity (absolute amount) - way too much or too little 3) How rapidly one enters into the hazard zone (rate of change) - not enough time to prepare/adjust to the change Hazard Event: Losses and Gains • Example of losses: during 1998 ice storm; -trees were cut down -power was out -roads were icy • Gains -tree cutting companies benefited -places that sold generators gained Factors that determine when does a hazard event becomes a Disaster or even worse Catastrophe: • Intensity • Population (number killed or injured) -group vs. injury • Property loss • Area effected • Geographic location affected (example at an oil resource) • Relief preparedness (ex. Haiti; hard to bring in relief supplies) • reconstruction time --> Why is the distinction between Disaster and Catastrophe important? a) governmental/world aid b) historical perspective -how often to these big events occur? Geology 106 Truism in Disasters: • 90% of the deaths are in the less industrialized countries -industrialized countries have a better economic advantage in order to build structures that are more ready to with stand a number of different disasters • 75% of economic damage is in the More Industrialized countries - when disasters occur it cost more money to rebuild the structures in industrialized countries What type of hazard is responsible, on average, for the most deaths? 1) Civil strikes 2) Drought 3) Earthquakes/Volcanoes 4) Storms/floods 5) Other (e.g. epidemics) Definition of RISK • Probability of moving into the hazard zone • (The probability of the hazard occurring or PH) x (The severity of the consequences of the hazard happens or SH)) Example: Bumping toe PH = 1/2 (50% chance of bumping toe) SH = 1 (severity of bumping toe; i.e. pain severity) ---> PH x SH --->1/2 x 1 = 1/2 Therefore the risk of bumping toe is 1/2 • How do we measure PH and SH? • Empirical observations and scientific studies (done by engineers/scientists) • Social/economic impact studies Should you believe the “experts”? • Wise to add a margin of safety in risk analysis -concept of SAFETY FACTORS; important to do this in the case that experts may have under estimated the risk -however, although it is important to have a safety factor it is not good to have too much of a safety factor because it may not not always be realistic How much RISK are we willing to incur? • once you have the “data” (i.e. determined values of PH and SH) -make your choice -it is entirely a matter of personal/societal choice Week 2 - Lecture 3: Earthquake Risk Analysis and Risk Management Fungibility: “a person and society, needs to seek a prudent balance between the advantages of boldness and the advantages of caution” Geology 106 ---> there are almost always opportunities forgone when we take precautions, and danger accepted when we do not People perception of RISK vary with the nature of the RISK • Involuntary hazard- tend to think it is riskier • Voluntary RISK- tends to seem less riskier • We are not very good at logically figuring out what the RISKS are Scenario: for proposed nuclear power plant on Lake Ontario shore just west of Kingston • The government of Ontario proposes o build a nuclear reactor on the shore of Lake Ontario near Kingston • Our task: carryout risk analysis and risk management study for the government, focused on seismic risk (i,e. earthquake risk) - need to look at the general approach to the risk analysis and risk management RISK Analysis: 1) understand the hazard a) what causes the earthquakes? b) where do earthquakes occur? c) what energy do they release? d) what exactly causes the damage? 2) Determine the RISK from that hazard for the region of interest (PH x SH) RISK Management: 1) determine ways to reduce PH and/or SH 2) do a “cost” benefit analysis; determine what you can afford - cost can refer to more than just an economic cost but also environmental, social and “personal choice” 3) implement mitigation techniques if warranted What Causes earthquakes? ---> movement on FAULTS: Fault: a break/crack in rocks along which there has been appreciable displacement Elastic Rebound Theory: the rigid part of the earth can store elastic energy; when it breaks the elastic energy is released Earthquakes are associated with Faults • Earthquakes happen when either a) A fault forms or b) There is an episode of movement on a pre-existing fault ---> In both cases, stored energy is released How do we recognize a fault? ---> look for rock/soil layers that have been shifted • There are 3 kinds of faults 1) Strike slip: horizontal motion 2) Dip-Slip Fault: sub-vertical or vertical movement; results in fault scrap (down the ramp) 3) Reverse Dip-Slip (up the ramp) Week 3 - Lecture 1: Earthquake Risk Analysis (understanding the hazard) Notes: many rivers occur along faults because the broken up rocks can be ore easily washed away • we often build DAMS on such rivers because the rivers make canyons Geology 106 1) Understanding the hazard: A) What causes the earthquakes? - motion on faults B) Where do earthquakes occur? C) What energy do they release? D) What exactly causes damage? WHAT CAUSES EARTHQUAKES? Focus: the point source of energy release on the fault Epicenter: the point at the earth’s surface that is directly above the focus How do you find the EPICENTER? • One way to find where the epicenter is to see where the damage is • Use seismometers; allows for: - detection of energy from a quake - measures the the distance to an earthquake and thus locate it - measures the energy released during an earthquake How do we find the FOCUS? • In other words how far away is the earthquake? - first we need to know about seismic waves Seismic waves: radiate from the focus of an earthquake as body waves • - when body waves reach the earths surface some of the motion gets transformed into surface wave motion • Surface wave: is the motion that is the most damaging to human structures; two types of surface waves... - RAYLEIGH waves: circular motion - LOVE waves: horizontal/side to side motion • Body waves: 2 kinds of body waves - P-waves: push-pull motion (compression-rarefaction) - S-waves: shear; wave motion What is the VELOCITY (speed) of seismic waves?: The velocity of P and S waves depends on ELASTICITY/DENSITY of the material they are passing • through • the more elastic a material is, the higher the seismic velocity is WHERE DO EARTHQUAKES OCCUR?: Focus: “point” of energy release on a fault. It is a whole line of energy, but considered a pin-point • scale wise. • Epicentre: directly above the focus on the surface of the earth. It is important because it’s the closest place to the focus at Earth’s system Week 3 - Lecture 3: Earthquake Risk Analysis (understanding the hazard) note: go to WHAT ENERGY DO EARTHQUAKES RELEASE? How do we estimate the energy released from a “quake”? 1) Measure the INTENSITY Geology 106 ---> based on observed damage (e.g. MERCALLI SCALE) • subjective • varies with distance from epicenter How do we estimate the actual energy released from an earthquake? • Measure the RICHTER MAGNITUDE - a quantitate measure of energy released; determined from the maximum S-wave amplitude/ on a seismogram • Each integer on the scale represents an amplitude difference of 10 (each integer higher would represent 10x the amplitude of the integer previous; logarithmic scale) • Open ended scale: unknown how big of an earthquake may arrive • The largest earthquakes ever recorded are ~ 9 on the Richter Scale - quakes < 2.5 magnitude are not felt by humans; note: but these low-energy quakes may be important for our nuclear reactor • Each magnitude integer step corresponds to approximately a 30-fold difference in energy release How much more energy is released in a magnitude 7 earthquake than in a magnitude 5 earthquake? • 30x30 = 900; 900 times the energy from level 5 to 7 What do the the Richter numbers mean in terms of actual energy released? ~ How would you figure that out? • Compare to unknown explosions (e.g. nuclear blasts) Note: Largest earthquake recorded: Chile, 1960 (M: 9.5); equivalent to annual U.S.A. energy use How frequent are earthquakes? • “Big” earthquakes happen rarely • Many small earthquakes • < 3 ---> over 100,000/year • > 3 ---> over 30,000/year • > 6 ---> 100/year • > 7 ---> 20/year Power Law relations: further elaboration in another lecture - on a LOG-LOG plot - you get a straight line How do we find the focus, the epicenter and the energy released?: • By simple observation of where the damage is greatest, or use the seismometer • Inertial mass; a mass at rest rends to stay at rest. It wants to stay at rest even though the spring’s shaking like crazy—so is the ground. So paper squiggles while mass does not, resulting in squiggly lines drawn on paper. To find the focus, or how far away the earthquake is, we need to first know what seismic waves are and how they behave. 1) Seismic energy waves radiate from the focus as body waves 2) When body wave motions reach surface, some get transformed into surface wave motions, which is most damaging to human properties. WHAT EXACTLY CAUSES THE DAMAGE? ~ Determine this by: a) Empirical observations Geology 106 b) Lab experiments c) Computer modeling d) In general: 1) the closer you are to the quake, the greater the damage 2) the greater the magnitude of the quake, the greater the damage BUT: this is modified by natural and anthropogenic conditions • Natural: nature of soil/rocks • Anthropogenic: nature of the structures that we build List of Earthquake Hazards: 1) Surface Faulting: structures on the fault will be disrupted by the tearing motion ---> so don’t build right on active faults 2) Ground Shaking: this is generally the greatest threat to buildings and people - In a big earthquake the shaking can be severe even 100’s of kilometers away from the epicenter • Most ground-shaking damage is generally a direct consequence of SURFACE WAVE motion 3) Ground Failure 4) Tsunami Week 4 - Lecture 1: Earthquake Risk Analysis (understanding the hazard) WHAT CAUSES DAMAGE CONT’D 1) Ground Shaking Material Amplification Effect: • When seismic waves SLOW DOWN as they go into another material -some of the energy is transferred into a greater shocking • Rock: least shaking Sand soil: intermediate shaking • • Clay Soil: most shaking • The amount of shaking also depends on the nature of the soil/rocks in the area -soft soils (e.g. clays) shake more than stiff soils (e.g. sand) which shakes more than rock Aftershocks: • Smaller earthquakes that occur soon after the “main shock” with epicenters in the same area as the main shock • Soon? ---> anywhere from minutes after the main shock to a year after • Aftershocks can cause the collapse of already damaged buildings 2) Ground Failure a) Landslides; rocks and/or soils -e.g. Hegben, Montana U.S.A. (1959) -e.g. Yungay, Peru (1970) b) Liquefaction of soils -sand or clay soil that changes strength when shaken -can flow like a liquid ~ e.g. Alaska (1964) ~ e.g. St. Jean Vianney, Quebec (1971) Geology 106 3) Tsunami Japanese word for harbour wave • • Colloquial: tidal wave • Seismic sea wave • Generated by earthquake at sea; fault located on ground level of sea that causes a ripple effect in waves on sea level eventually causing a tsunami at shore • How Tsunamis work: Tsunami-genesis; the process of the generation of Tsunamis • Tsunami waves: velocity in open ocean: 500 to 800 km/hr (= speed of passenger jet plane) • When a tsunami wave reaches shore, the wave slows, and the water piles up to heights as much as 60 meters (18 story building) or more Week 4 - Lecture 2: Earthquake Risk Analysis (understanding the hazard) WHAT CAUSES DAMAGE CONT’D Tsunami’s CONT’D Dip Slip Faults (up and down motion) are usually more likely to cause a Tsunami as opposed to a strike • slip fault (horizontal motion) What about a Tsunami on Lake Ontario? • Probably not a very big tsunami -maximum height ~2 meters • Why? ~ because of shallow water depth a) leads to only a small amount of water being displaced b) speed of Tsunami is low BUT: a big lake Tsunami could cause a big Tsunami ~ ex. Switzerland: Geneva Lake Tsunami of approx. 10 m in height; mountains were around the lake. • Having big mountains around a big lake would contribute to more water being displaced therefore causing a larger Tsunami • Thankfully, there are no high, steep mountains surrounding Lake Ontario Tsunami Causes: 1) “Seafloor” earthquakes 2) “Underwater” landslide 3) Collapse of the flank of a volcano into the sea 4) Submarine volcanic explosions 5) Impact of meteorite into the ocean 4) Fires e.g. the 1906 A.D. “fire” in San Francisco 5) Disruption of water supplies and/or disease outbreak e.g. Cholera outbreak in Haiti following earthquake 8) Human induced Seismic Hazards a) Dam Construction • Loading of earth by water changes the stress regime; earthquakes can happen • Water can infiltrate below dam and can “lubricate” faults potentially causing earthquakes to happen; possible dam failure b) Mining • Underground mine shafts - threat of rock bursts (change in stress regime cause cracks in rocks) Geology 106 Week 4 - Lecture 3: Risk Analysis (Determine the RISK from that hazard for the region of interest) Asses seismic risk of area: 1) Locate and determine nature of fault in the area 2) Study history of earthquakes in the area 3) Determine the geologic/geographic factors in the area 4) Determine human interactions with the potential hazard in the area Does every fault produce earthquakes? • NO! -Some are INACTIVE; has not moved in last 2 million years (m. y.) -Some are POTENTIALLY ACTIVE; has not moved in last 2 m. y. -Some are ACTIVE; has moved in last 10,000 years Are there faults in the Kingston area? • YES! -All the way from small ones, up to very big ones; like the St. Lawrence River Assessing Seismic Risk!!! Note: in order to figure out if any of the faults are active it is necessary to study the history of earthquakes in the area 1) Locate and determine nature of faults in the area A) Look on the ground, and from the air (and space); BUT there can be hidden faults B) Set up seismometers to help locate faults; only effective for faults that have moved since seismometers were set up • NOTE: fault zones are very complex 2) Study history of quakes in the area A) Set up seismometers • gives an idea of which faults are most active • gives some idea of frequency and magnitude of quakes; critical to collect as long of a seismic record as possible • Ex. look at Canada; where are the zones that are prone to earthquakes?; is the Arctic region high risk? - NO (because population is low); lets look more closely at Western Canada and Eastern Canada B) Determine the RECURRENCE INTERVAL for “big” earthquakes in the area (how often to “BIG” earthquakes happen?); “BIG” means greater than magnitude 7 Note: Power-Law Relationship: # of earthquakes on Y axes and magnitude of earthquake on X axes • Look at human historical records; goes back before seismometers • Dig trenches and pits on the active faults; identify ancient (big) fault movements Week 5 - Lecture 1: Earthquake Risk Analysis (Determine the RISK from that hazard for the region of interest) 2. Study history of quakes in the area: RECURRENCE INTERVAL (b) CONT’D: B) Determine the RECURRENCE INTERVAL for “big” earthquakes in the area (how often to “BIG” earthquakes happen?); “BIG” means greater than magnitude 7 Note: Power-Law Relationship: # of earthquakes on Y axes and magnitude of earthquake on X axes • Look at human historical records; goes back before seismometers Geology 106 • Dig trenches and pits on the active faults; identify ancient (big) fault movements Relative Time: 1) “Law” of Superposition: order of sediment layers, oldest are on the bottom; youngest on top 2) “Law” of ... : Step 1: determine the RELATIVE age of the fault ~ Determine an ABSOLUTE age bracket for fault movement using carbon-14 dating of organic peat Step Note: 14c daring (and other radiometric “dating” methods) can be used to determine when a fault last moved (if your seismometer1s haven’t already told you the answer!) i.e. Is it active? Step 2: PEAT layers contain dead organic matter; can determine the time since the organic matter died can be determined by the C14 method (Carbon-14) • Look for evidence of ancient tsunamis and ground elevation/subsidence ~ Tsunami: use Carbon 14 dating ~ Ground Subsidence: date of “old” quakes; use C-14 method -these events can instantly bury swamps with sand -you can “date” the dead organic matter (C-14 method); this gives you the age of the quake Example of RECURRENCE INTERVAL (LA, California) ---> 9 major events in 1400 years; therefore RECURRENCE INTERVAL is 160 years C) Construct Probability and Earthquake-Hazard maps Map out locations of rock, sand soils, clay soils, etc. • -they have variable shaking characteristics • Map out zones of clay/sand that are prone to liquefaction -on a map that marks areas that are prone to liquefaction; the red zones represent prone areas to liquefaction and the brown/sand colour areas represent the areas that are not prone • Map out locations of cliffs/hills that are at risk if landslides • Map out tsunami hazard zones -shore lines of oceans (and lakes but tsunami will be small; unless it is close to steep mountains) 3) Determine geologic/geographic factors in the area... (finish/figure out this part) 4) Determine the potential human interactions with hazard in the area A) What is the distribution of the population in the area? -particular attention to prominent of people to high risk zones B) What is the nature of the human infrastructure; where are the buildings and roads with respect to high risk zones Week 5 - Lecture 2: Seismic Risk Management RISK MANAGEMENT 1) Determine ways to reduce PH and/or SH 2) DO a “Cost” - Benefit analysis; determines what you can afford to do Geology 106 3) Implement mitigation techniques if warranted Determine ways to reduce PH and/or SH A) apply land-use planning and zoning • Use high hazrad areas for low population use (e.g. parks, golf courses) • In particular, don’t build in areas of soft soil or soils that might liquefy B) Apply stringent building code • Choose appropriate building materials; materials can be broken up into GOOD and BAD building materials. GOOD materials would be; wood, steel, reinforced concrete (the good materials are ALL flexible). BAD materials would be stucco, adobe, unreinforced concrete, heavy masonry (The bad materials are inflexible) • Choose resistant building design. The worst damage occurs when the PERIOD VIBRATION of the ground and the building are the same. {Note: Building have a natural period of vibration ~ N/10seconds ; N = # of stories} -How to build a resistant house: Bolt t, Bracket it, Brace it, Block it, Panel it • Legislate and enforce regulations about construction; this ensures that builders do A) and B) Week 5 - Lecture 3: Seismic Risk Management Determine ways to reduce PH and/or SH C) Set up warning systems and emergency-response plans • Set up Earthquake warning systems and tsunami early-warning systems -Radio waves travel faster than seismic waves, so we can set up seismometers near faults -When they detect a quake, they transmit a radio signal to the more distant cities ~To minimize tsunami damage; Early warning system; sensors on ocean floor that detect sudden changes in ocean depth: -Maintain natural shorelines; mangrove trees lessen impact of tsunami wave -Limit population centers along shoreline -Provide tsunami education/training • Provide appropriate emergency equipment and personnel -prepare emergency response plans • Educate the public -Information booklets -Earthquake D) Try predicting an earthquake -Benefits are that people can evacuate and areas can prepare • Long Term Prediction -Determine the recurrence intervals -Look for seismic gaps; these are high risk areas... the stored energy is not being released but when it finally does it could be a very big earthquake; this happens because the fault is “locked” Week 6 - Lecture 1: Finishing off Seismic Risk Manage
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