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Chapter 1-6

Earth Science - Chapters 1-6 Notes.docx

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Department
Earth Sciences
Course
EARTHSC 2GG3
Professor
Sergei Basik
Semester
Fall

Description
CHAPTER ONE: NATURAL HAZARDS AND DISASTERS Mitigating Hazards  Mitigation: efforts to prepare for a disaster and reduce its damage (ex. levees, government policy, education) Land-Use Planning  Land-use planning: find out where disasters are likely to occur and restrict development there  Reserve land for parks and natural areas  Limit housing/industrial development on floodplains, near the coast, near active volcanoes  Hard to do this because people want to live close to coast, river, etc. and will fight against land-use restrictions  Developers, companies and governments allow people to move into hazardous areas  Deny the existence of hazards  Do not want to lessen value and scare off clients Insurance  Insurance: shields people from major losses they cannot afford  Lessens financial impact of disasters  Risk: o A hazard considered in the light of its recurrence interval and the expected costs o Greater hazard and shorter recurrence interval mean greater risk o Hard to estimate the recurrence interval  Private insurance companies do not want to offer disaster policies because could put company out of business  Earthquake insurance is available where there are few earthquakes (ex. Texas)  Insurance not available for landslides, mudflows and ground settling The Role of Government  US Geological Survey (USGS) and Geological Survey of Canada (GSC): o Earthquake and volcano research o Study and monitor stream behavior and flow  National Weather Service: o Monitors rainfall and severe weather o Uses its data and data from USGS to predict storms and floods  Federal Emergency Management Agency (FEMA): o Created to bring order to chaos of relief efforts that emerge after natural disasters o Focuses on relocating victims rather than rebuilding in original unsafe location o Want to minimize potential losses  HAZUS (Hazard United States): o Computer system used to determine risk levels and estimate loss potential from earthquakes o Includes potential hazards, inventories of hazards, direct damages, induced damages, direct economic and social losses, indirect losses o Provides funds for victims o Only starting to eliminate the cause of future disasters  Government policy can be counterproductive: o Federal tax code subsidizes building in safe and hazardous sites o Real estate developers get tax deductions o Small Business Administration disaster loan program subsidizes credit to finance rebuilding in hazardous locations The Role of Public Education  Most people think that it won’t happen to them  May not listen to warnings until something happens to them or a friend  Do not have tools predict specific locations/timing of natural hazards  Emergency Management Institute: provides workshops and courses to educate public and government on natural hazards  Best window of opportunity for effective hazard reduction is immediately following a disaster of the same type (two or three months)  Public education is successful when: o Info comes from multiple credible sources o People have written material to refer to o There is discussion among potentially affected groups o People think risk is plausible Living With Nature  Humans want to stop damage by controlling nature  Cannot always predict or build barriers  Trying to prevent hazards just directs them to a different place or time Chapter 2 (page 17-18) CHAPTER TWO: PLATE TECTONICS AND PHYSICAL HAZARDS Plate Movement  Lithosphere is broken into plates  One plate may spread over a continent area and a ocean area  Plate tectonics: theory that describes the movement of Earth’s plates  Divergent boundaries: plates move away from each other  Convergent boundaries: plates move toward each other  Transform boundary: two plates slide past each other  Oceanic plates collide: subduction zone is formed when the denser plate is subducted into the asthenosphere  Continental plates collide: neither side dense enough to slip under so create mountains  Seafloor spreading: when new oceanic crust spreads apart  Trenches: top of the subduction zone  More than two different plate boundaries can intersect  Ex. Mendocino triple junction: off the northern California coast Development of a Theory  Alfred Wegener (1912): continents were originally part of one giant supercontinent – Pangaea  North and South America separated from Europe and Africa  Continental drift: continents drifted through oceanic crust, forming mountains along their leading edges  Similar rocks in southern parts of Australia, South America, India, Africa  Mid-oceanic ridge: immense mountain range down the center of the Atlantic Ocean  Said ocean floors were like conveyor belts that carried the continents (not actually true – was the magnetism)  Earth has a magnetic because slow convection currents in core generate magnetic field  Magnetism was stronger where rocks solidified while magnetism was pointing to north magnetic pole  Magnetism was weak where rock magnetism was pointing toward south magnetic pole CHAPTER THREE: EARTHQUAKES AND THEIR CAUSES Tectonic Environments of Faults Transform Faults  San Andreas Fault: stretches from San Francisco Bay to Los Angeles  Main sliding boundary marks the motion between the Pacific Plate and the North American Plate  Blind thrusts: o Plate thrusts that do not break the surface but rather create a tight fold o Dangerous because remain unknown until cause an earthquake  Strike-slip faults: faults that do break the surface  Result of overall horizontal compression is diagonal dipping faults Subduction Zones  Most important example of subduction-zone faults in US is in the Pacific Northwest (between Cape Mendocino in California and BC)  Sudden shifts of ocean floor can cause tsunamis  Largest recorded earthquakes since AD 1700 have occurred in subduction zones  Major earthquakes happen after a build up of time and energy  Evidence of ancient major earthquakes foreshadow future major earthquakes  Giant earthquakes in southern part of subduction zone occur at intervals as short as 250 years  Earthquakes on major faults can trigger earthquakes on adjacent faults  80% chance of a giant subduction-zone earthquake along southern part of fault off Oregon and California in next 50 years  Earthquakes can happen above the subduction zone (ex. Seattle Fault) Continental Spreading Zones  Best known area of continental extension is Basin and Range of Nevada, Utah  Has numerous north-trending faults that separate raised mountain ranches from dropped valleys  Fault zones that created valleys and mountains are still active  Are capable of causing major earthquakes CHAPTER FOUR: EARTHQUAKE PREDICTION AND MITIGATION Populations at Risk  Seismologists can develop a risk map  Risk map: estimates risk of an earthquake for a given area  Maps based on past activity of frequency and magnitude  Used to choose sites for dams, power plants, public buildings, bridges and for insurance purposes  Highest risk area in US is California  Forecasting allows scientists to estimate probability of earthquake and levels of damage  99% chance of an earthquake with magnitude 6.7 or larger in California in next 30 years The San Francisco Bay Area  San Andreas Fault includes almost all of San Francisco Bay area  Most significant earthquake was in 1906  Gutenberg-Ritcher frequency-versus-magnitude relationships says: o Fault should have a magnitude 6 earthquake every 8 years o Should have one of magnitude 7 every 700 years  Energy builds up across fault until earthquake occurs  Chance of major earthquake grows as time since last large earthquake increases  Potential damage earthquake can cause increases as well  Hayward Fault and Rodgers Creek Fault also add risk to San Francisco area  People build right on top of fault  Will cause more damage than historical earthquakes since there are more buildings to be ruined The Los Angeles Area  San Andreas Fault is 50km northeast of Los Angeles  Earthquakes along fault cause damage in Los Angeles too  Can also cause moderate earthquakes in Los Angeles CHAPTER FIVE: TSUNAMI Tsunami Generation  Tsunami: Japanese name for “harbor wave”  Waves are highest where they are focused into bays/harbors Earthquake-Generated Tsunami  Most tsunamis generated by earthquakes from sudden rise/fall of seafloor  From displacement of ocean floor on a reverse/thrust fault movement, on a subduction-zone fault  Strike-slip earthquakes do not displace much water so don’t normally create tsunamis  Coastal bulge: continental plate is pulled toward the continent as the subducting plate moves under it at a subduction zone  When stuck zone ruptures the continent snaps up (earthquake) and displaces huge volume of water (tsunami)  Height of tsunami wave depends on: o Magnitude of earthquake o Area of rupture zone o Rate and volume displaces o Sense of ocean floor motion o Depth of water above rupture  Size of earthquake-generated tsunami is limited to maximum displacement on a fault  Most dangerous parts for tsunamis in US and Canada are: Hawaii, California, Oregon, Washington, British Columbia, Alaska Tsunami Generated by Volcanic Eruptions  Water can be driven upward by fast-moving flows of volcanic ash or submarine volcanic explosions  Cannot estimate maximum size of tsunami from volcanic eruption  One of most catastrophic: o Krakatau in 1883 o Volcano under water exploded o Upward displacement of large amount of seawater o 35mins later waves reaching 30 meters flattened coastline o More than 35,000 people died Tsunami from Fast-Moving Landslides or Rockfalls  Fast-moving landslides/rockfalls can enter ocean and displace large amounts of water  Height of the fall determines height of tsunami more than volume of mass that falls into water  Highest tsunami in history: o 1958 tsunami in Lituya Bay, Alaska o Earthquake detached large section of cliff o Only killed two people  Submarine landslides: landslides that occur underwater  Tsunami can also occur in large, deep lakes (ex. Lake Tahoe on the California- Nevada border) Tsunami from Volcano Flank Collapse  Flanks of major volcanoes can collapse and slide into ocean  Displace thousands of km of water  Can create tsunamis that are hundreds of meters high  Ex. volcanoes that make up the Hawaiian islands rise from the seafloor and while they are rising mega-land sliding occurs  Lower part of volcanoes is formed of erupting lava that has chilled in the seawater  Enormous segments of volcano can break off i
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