Planet Earth Exam 3 Earthquakes Cant predict earthquakes but can estimate risks Japan 2011 Tohoku Quake o Magnitude 9 4th largest since 1900 8805 dead 12664 missing Definition o Rock under stress applied push pull or shear o EQ occurs when stress is greater than rock strength friction o Fault movement releases stress as vibrations faulting is brittle Slip and Displacement Distance of offset o Mm to Cm of displacement in small quakes o Can be as big as 2 7 m 1906 San Fran EQ Focus or Hypocenter place within earth where rock ruptures Epicenter focus projected to surface Fault scarp area exposed when fault moves Fault Types o Normal extension Reverse compression Thrust Compression Strike Slip Regional Stress Elastic Rebound Theory o Rocks store elastic energy when plates move causing strain and causes to change shape o When stress is too great energy is released and causes movement o After stress released rock snaps back to original shape o Snap back to shape causes the vibrations Asperity protrusion in surfaces Body Waves fastest waves o P Waves compressional waves Primary first and fastest Material moves back and forth in direction of wave o S Waves shear waves Secondary second and slower 60 velocity Material moves is up down in wave direction Surface Waves o Move along the earths surface slower but cause more damage o Rayleigh R waves resembles water ripple o Love L waves sideways s wave fastest Seismograph records vertical and horizontal ground motion on seismogram Locate epicenter through triangulation Three Scales o Modified Mercalli Intensity Scale Defined by amount of destruction and damage Subjective based on strength distance surface materials and building design intensity amount of damage not magnitude o Richter Magnitude Scale Largest ground motion surface waves at 100km distance Need 2 0 or greater for humans to feel less than 5 isnt severe Scale is 0 10 but logarithmic largest was 9 5 o Seismic moment magnitude Scale slip amount x rupture length x rupture depth x rock strength o Seismic belts Waditi Benioff zone subsuction zone at convergent Where do earthquakes occur boundary intraplate Earthquake Damage o Intensity and duration of vibrations o Damage caused by surface waves o Depends on character of the substrate rock v fill proximity to hypocenter frequency ground acceleration o Causes landslides fire disease tsunamis Mountains Faults Folds Deformation Deformation o Change in location orientation shape or volume o Due to applied stress Structure Orientation o Plane o Line Strike angle of imaginary horizontal line on plane measured from north Dip maximum angle of plane s slope Bearing compass angle of a line Plunge angle between line and horizontal Stress force per unit area acting on a rock to change shape and or volume Strain change in shape or volume from stress o Main kinds are compression shortening tension stretching shear sideways o Fossilized shell is good strain indicator Deformation Types o Brittle material breaks discontinuous low temp and pressure o Ductile material flows without breaks continuous high temp and pressure and in salt and shale o Dependent on temperature pressure deformation rate composition Fractures o Faults Crack with relative movement Recognized by offset displacement slip fault scarp drag folds fault breccia gouge slickenslides slip lineations Brittle and discontinuous rapid deformation rate Mylonite actually ductile but depends on temp pressure and comp o Folding Ductile Continuous deformation slow deformation rate Creates anticline arch syncline trough monocline dome and basins Intersect earth at angle or plunge Dome strata older in center basin strata younger in center Mountain Building Active Mountain Ranges o Linear range of mountains Orogeny mountain building event processes that collectively prodice a mountain belt o Most mountain building occurs at convergent boundaries Methods to make mountains o Orogenesis of a volcanic island arc Aleutian Type Shrinking ocean basins such as Pacific Across subduction zone o Orogenesis along continental volcanic arc Andean Type Igneous intrusions Plutons Thrust faulting Underplating Regional metaphorism o Continent Continent Collision Himalayas come from collision of india and asia Suture zone where two land masses are joined o Continental Accretion Small crustal fragments collide and accrete to continental margins Terranes accreted crustal blocks Cratons crust that hasn t been deformed in a billion years o Mountain building associated with Rifts Continental thinnging Normal faults and block rotation Footwall can go up Narrow elongate ranges Death of a mountain range Isostasy Archimedes o Erosion and resulting of isostatic adjustment of the crust o Concept of floating crust in gravitational balance o Force pushing up force pulling down o Buoyancy gravity Case Study Appalachians o Complex orogenic belt formed by 3 orogenic pulses o Appalachians today are eroded remnants Energy and Mining Whale Oil o Came before petroleum products o In demand in 17 1800s used for lube and burning lamps Fossil Fuels modern energy staple o Coal Oil and Natural Gas o Produced by organic debris deposited throughout geologic time o Large accumulations of organic matter o Burial Small percentage of material remains to generate fossil fuels dependent on paleo environmental conditions o Reverse solar energy Nonrenewable resources finite and exhaustible over human time scale Large accumulations of organic material in anoxic basins and swamps Carbonaceous Sedimentary Rocks o Coal Oil Shale and asphalitic substances Oil and natural gas are not rocks o Organic matter incorporated into sediment Carbon o Remainder of sediment siliciclastic carbonate material o Generally accumulates in restricted basins and stagnant swamps and Low oxygen environment more organic matter than oxygen bogs Coals o Most abundant carbonaceous sediment o Combustible organic matter o Impurities of ash siliclastic material o Compacted plant material o Found in low oxygen swamps and marshes o 50 weight organic material threshold 70 volume o Onslaught 290 354 m y Coal Formation Deposition Compaction Induration o Accumulates in anoxic marsh and swamp enviroments Rapid burial prevents decomposition Accumulation is greater than decomposition from microbial and chemical processes Water table close to peat surface o Deposited in temperate mid latitudes in geologic past Peaked in Devonian Carboniferous Temp reach is greater than 200 degrees centigrade Coal