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This 13 page Class Notes was uploaded by Sigmund Corwin on Saturday September 19, 2015. The Class Notes belongs to GEOL105 at University of Delaware taught by SusanMcGeary in Fall. Since its upload, it has received 43 views. For similar materials see /class/207145/geol105-university-of-delaware in Geology at University of Delaware.
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Date Created: 09/19/15
Geology105 262012 20300 PM NATRUAL HAZARDS INTRO Hazard o Natural process that is a threat to human life or property Disaster o Hazardouss event that occurs over a limited time in defined area o Critieria one or more of the following o 10 or more people killed 0 100 or more people affected 0 state of emergency is declared 0 international assistance is requested Catastrophe o Massive disaster that requires a significant amount of money andor time to recover The size of a hazardous event if inversely related to how often it occurs ON FINAL Deep Earth Hazards hazards where it s the energyheat inside the planet earth is hot provides the energy for hazards o Earthquakes o Volcanoes o Tsunami Surface Hazards Energy comes from the sun o Floods o Climate Change o Hurricanes Disaster Trends o Recently there has been an increase in the amount of natural disasters 0 Not necessarily true actually Number of tsunamis and stuff are constant The impact they have however is bigger because there are more and more people o Disasters are now becoming catastrophese 0 World s pop is growing Fundamental Concepts for Understanding Natural Processes as Hazars o Hazards are understandable from scientific evalution o Risk analysis is important o Consequences of hazards can be minimized o Mitigation What you do to try to minimize the impact Land use planning Engineering buildings and structures Insurance Education o Linkages exist between different natural hazards and between hazards and the physical environment Approach to Natural Hazards o Identify location of hazard where and size how big o Determine recurrence interval and probability of event how often o Estimate cost of even how much and determine risk o Make a forecast or prediction 0 Prediction vs forecast Prediction includes where how big and when An example there will be a magnitude 7 earthquake in Newark DE tomorrow Forecast where how big and probability of event occurring Ex there is a 62 probability of a M7 or greater EQ in the San Francisco bay area before 2032 o Observemonitor any precursor activity and proide warning o Mitigate Educate Mitigate Educate Planning to avaoid death and destructin by Natural Hazards o Thinking about hazards like a geologist 0 Map the location of faults This isn t that hard to do when they re active 0 We cause motion along a fault How often a Recurrence interval o Average amount of time between events ON EVERY TEST AND FINAL Average interval o Say the recurrence interval is 20 years you can work out the probability in any given year is That is the reciprical The probability would be 120 chance of there being an earthquake that year Risk n Cost of single event x probability o Determining a recurrence Interval o If lines are far apart but not consistant intervals between earthquakes are highly variable And timing of future earthquakes cannot be predicted based on when the last earthquake occurred You only know the probability each year 0 The average interval add up the intervals and divide by 100 Second method take date of last disaster date of earliest disaster and divide by number of intervals o Important points to remember 0 Definitions natural hazards natural disasters catastrophese reccureceinterals 0 Why the cost of natural disasters is increasing expoentitially o The geological approach to dealing with natural disasters Understand causes 0 Quiz 1963 9 1988 n intervals 34567 a recurrence interval 5 years a probability 20 n in what year after 1988 will the next earthquake occur there is no way to know You move into an earthquake prone area and discover that there were 6 major earthquakes over a period of 300 years 171017761812 1914 1942 2010 a What is the RI 60 years a When will the next earthquake occur there is no way to say Earth Materials o Planet Earth 0 Surface layer crust Made up of rocks n Rocks are made up of minerals Minerals are compounds formed from atoms 0 Atoms are basic building blocks of elements Each element has a specific number of protons Composed of protons neutrons 0 and electrons Protons and neutrons have a mass Electrons have very minimal measurable mass Different isotopes of an element have different numbers of neutrons Carbon 14 has two extra neurons We use it to date things Some isotopes are unstable and decay over time they are radioactive From minerals you make up atoms Minerals must be 0 Natural 0 Inorganic 0 Have a specific chemical composition Ex quarts has a chem Comp of SiOZ 0 Must possess a crystalline structure Minerals 0 Quartz potassium feldspar and plagioclase feldspar is harder than glass and difficult to break 0 Clay minerals Silicate mineralsanother word for clay formed by weathering of other silicate minerals Typically found as groups of very small paricals O O O The most common mineral in the rock shale Clay minerals are very weak a Easily deformed Think of squishing mud in your fingers o Important things to know 0 Elements consist of protons neturons and eletrons o Isotopes of an element have the same number of protons but different number of neutrons 0 Definition of a mineral o Quartz and feldspar Hard strong silicate minerals The primary consitituents of the rock GRANITE 0 Clay Weak silicate mineral that is found as very small platy particls MORE ON SLIDE o Questions 0 018 is heavier than 016 o On earth lots of water is evaporated from the ocean every day liquid h209 gas The process of evaporation prefers to evaporate h20 molecules with the lighter 016 isotope what happens to the water left in the ocean The water in the ocean is heavier because it has a greater percentage of 018 Rocks c We classify rocks by how they re formed 0 1 Igneous Rocks solidfy from magma Magma is molton rock 0 2 Sedimentary rocks they form from sediment Sediment is from the weathering of rocks at the earth s surface Weathering transportation of sediment deposit lithification Sandstone shale limestone They break down to small things called sediments o 3 Metamorphie rocks form when rocks are exposed to high pressures and high temperatures When rocks are buried under miles of other rocks below the earth s surface Such rocks may be transformed into new rocks without melting o Granite crystalline texture All space is filled up o Sandstone sand packed together o Shale a sedimentary rock If its buried deeper can turn into slae which is a metamorphic form of shale If you burry that slate into something deeper itbecomes gneiss which has light and dark layers Geologic Dating and the Geologic Time Scale Relative age dating o Time sequence in which events occurred Absolute age dating o Date in years How old is earth o 46 billion yrs o youner layers form on top of older layers Principles allow geologist to pu together timescale for earch These are all relative age dating tools o Original horizontality o Lateral continuity o Super position 0 You know the oldest youngest positioning of the rock is because of super potioning o Crosscutting o If something is cut across you can see the layers 0 Geologic events that cut across FossHs The Principle of Fossil Succession o Sandstone limestone shale o Fossils indicate which are the same RELATIVE age in the two locations 0 Lines connect rock types of relative ages o Can be used to establish age equivalence 0 Between different rocks in different areas o This is the basisi for the geologic time scale o Cenozoic new life canids felines whales primates o Mezozoic dinos o Precand 0 Absolute Dating o Mostly basted on unstable elements isotopes that undergo radioactive decay 0 That decay occurs at known rates 0 A parent element spontaneously decays to form a daughter product The known rate of decay is it s half life 0 If the parent element starts at 100 at 1 half life it s at 50 At 2 half lives its at 25 f o This is useful in age dating take mineral to measure ratio of parent to daughter mineral 0 Half life time it takes of parent to decay to daughter These are constant c Minerals in the magma dike have been dated using radioactive elements with a halflife of 10000 years The analysis shows that there is 125 parent element and 875 daughter product left in the rock How old is the dike 0 30000 years old Era Absolute Ages o Cenozoic 65 my to present o Mesozoic 251 my to 65 my ended with mass extinction that knocked off dinosaaurs o Paleozoic 542 my to 251 my ended with biggest mass extinction known Earth structure and plate tectonics o Crust mantle liquid iron outer core 0 Inner most core Made up of iron and some nickel Inner core is solid and outer core is liquid The outer core is responsible for earth s magnetic field 0 Mantle solid rock Convects flows over geologic time o Crust solid rock Oceans iron rich Basaltic Continents silica rich Granitic 7km thick 70 km thick o How do you move electricity around 0 Conduction Slow process 0 Convection Movement of hot material transports the heat Cold material is denser and sinks and hotter material rises o Lithosphere o Outermost layer of earth based on rheology not composition Response do applied force Cold rigid strong About 100 km thick Broken into around 12 large plates these plates move with respect to each other o Asthenosphere 0 Below lithosphere o Warmer soft flows weak o Earth is also layered by its rheology different physical properties 0 Lithosphere is on top 100 kms thick 0 Asthenosphere o Plate Tectonic Theory 0 On earth our lithosphere is broken into pieces Those pieces are called plates The crust is part of the lithosphere ON TEST 0 The plates move horizontally o The plates move in different directions relative to each other 0 At plate boundaries or the edges of the plates there is tectonic activity This is where earthquakes occur volcanoes mountain formation and ocean formation TU KC 3 Types of plate boundaries 0 1 Convergent two plates move towards each other subduction when one plate goes under the other 910 of the biggest earthquakes occurred at subduction zones Subduction also creates volcanoes Convergent PB a Process Subduction o Tectonic Setting Subduction zones 0 Leading edge of an oceanic plate sinks beneath another plate 0 Ex cascades a Process Continental Collisions o Tectonic Setting major mountain belts 0 Continental leading edge collides with another continent 0 Ex ancient appalacians Current Himalayas alps o 2 Divergent move away from each other Divergent PB n 1 Process Sea floor o Tectonic setting mid oceanic setting o Spreading at midocean ridges Two broken pieces move away from each other a 2 Process Continental rifting o Tectonic Setting Continental rifts o the continent is being split in two o ex riogrande rift basin and range African rift system c magma moves through the crack and becomes part of the lithosphere o 3 Transform plate boundaries 0 side by side motion tectonic setting transform fault like san andreas n plates move laterally past each other between seafloor spreading centers a Big earth quakes but no volcanoes Delaware is not on an active plate boundary Fact o Something known from observation or experience Evidence o Facts or data used to support an argument Hypothesis o Model given as an explanation for observations or processes It s a provisional model to be tested or to guide inestigation o Working hypothesis 0 Sometimes you can use multiple of these Theory o A framework or set of explanations How plate tectonic theory developed 1960s o A history existence of pangia o 1 Jigsaw puzzle fit of continents o 2 Mesosaurus evidence 2 fossils this is a creature that existed in different continents So either they swam from one place to another or maybe the continents were together in pangeia o 3 Climate o mountain chain terminations o Wegener s Hypothesis 0 Continental drift 1912 0 He looked at the above evidence about pangea o B Plate Tectonic Theory and evidence 0 mid oceanic ridge 0 Paleontology 0 Age of seafloor Earthquakes o What causes earthquakes o Caused by sudden abrupt motion along a fault That releases energy which causes ground motion 0 Focus point The initial point of rupture Epicenter a Point perpendicular to the focus that is at ground level the focus point is under ground o Elastic Rebound Theory 0 Stress reaches elastic limit rock breaks It bends but goes back to its original shape 3 types of Seismic Waves o 1 P Waves 0 fastest o arrive first primary 0 solids liquid and gases o 2 S Waves Shear waves 0 second fastest 0 travel like a snake 0 can only travel in solids 0 Like flicking a rope o 3 Surface waves 0 travel along an interface travel along layers slowest can only travel in solids highest amplitude most damaging because of its high amplitude shakes ground a lot lasts a long time It also has the most complicated motion ON TEST o seismogram wiggle trace 0 ground vibration that is recorded 0 the further you are from the earthquake the further the lines in the seismogram are Global Seismographic Netowrk o different groups of countries making up a network o they study earthquakes How do we measure the size of an earthquake o 1 Intensity scale 0 measures what humans and buildings feel 0 Location distance from earthquake Usually the closer you are to the earthquake the higher the intensity Type of building higher up the more you ll feel it Type of ground o 2 Magnitude scale 0 based solely on the amount of energy released Only one value per earth quake Measure the maximum amplitude on a seismogram M log base 10 correction factors will not have to do on test Mag 6 gt5 by an amplitude factor of 10 6 has 10x the amplitude of 5 M9 is 100 time the amount of ground shaking as M7 o Amount of energy 0 1 Area of fault that ruptures fault has a length and depth Area l x d if you have a really long fault or really deep fault it will release more energy than a short or shallow fault o 2 Amount of slip on the fault 2 meters is less than 6 meters 0 3 Shear modulus stickiness of fault the more stuck together the fault the more energy it takes to break Where do we get the biggest earthquakes o Subduction zones have the longest and deepest faults so they have the biggest area so they should produce the biggest earthquakes o Continental collisions are also high in deadliness btu has to do with amount of people living there TSUNAMIS ARE NOT ON TEST 1
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