Japans 2011 Tohoku Earthquake Magnitude 9 4th largest eq since 1900 largest ever in Japan 8805 dead 12664 missing Tohoku EQ resulted from thrust faulting What is an Earth Quake rock under stress stress applied push pull or sheer stress rock strength friction movement fault movement realeases stress as vibrations faulting is a process of breaking therefore is brittle Slip and displacement distance of offset How much displacement occurs can be small mm cm during smaller quakes can be massive 1906 San Francisco EQ ruptured 430 km long by 15 km high San Andreas Fault entire length was displaced between 2 7 m 1964 Alaska Quake raised ground level 2 meters Focus projected to surface EPICENTER Focus actual center of movement on tectonic plate Epicenter projection of focus ontoearth s surface Fault scarp left over chunk of when fault moves Hanging wall part of earth that moves away and down Footwall part of earth that stays in place Fault Types normal fault hanging wall down due to extension reverse fault hanging wall up due to compression thrust fault low angle of displacement due to compression strike slip fault one thing sliding against each other Lateral movement right left lateral CLICKER place w in earth where rock ruptures and an EQ occurs is The Focus Elastic Rebound Theory Tectonic forces slowly cause rock to strain change shape Rock stores elastic energy Stress too great and energy is released Energy released as spherical vibrations No more stress rock snaps back to original shape Snap back elastic rebound causes vibrations Build up of stress can cause small quakes foreshocks before big one Also can have aftershocks after main quake as rock readjust Stick slip stress builds up fault slips Asperities friction resists sliding don t worry abt term movement along small cracks precursors to main event follows main quake 10x smaller fault readjusting to new stresses caused by major earthquake can exist days to weeks after basically means readjustment after fault moves 10x smaller than previous Types of Seismic Waves Body waves do not dissipate move w in the earth faster because vibrations move faster through solid materials Surface wave move along earths surface slower cause more structural damage Body wave types P waves Primary compressional P wave arrives first most efficient in transferring energy Moves back and fourth Fastest wave S waves Shear secondary wave Material moves up and down direction Moves as 60 of P wave velocity 40 slower than P wave Surface wave types Rayleigh R wave Moves up down side to side resembles an ocean wave Love L wave Resembles sideways S wave Fastest surface wave CLICKER Which seismic wave travels fastest Primary wave Seismograph records vertical horizontal ground motion Records quake on a seismogram Usually have 3 different seismographs at each location to measure N S E W Up down motion Triangulation method to locate where an EQ occurred precisely using 3 circles to pin point location KNOW HOW TO LOCATE EPICENTER FOR TEST EQ Sizes and Magnitudes 3 different scales Mercalli intensity scale defined amount of damage destruction its subjective depends on quake strength distance surface materials building materials Richter Magnitude scale log scale log base 10 largest recorded 9 5 5 considered severe 2 0 not felt by humans Seismic movement magnitude scale projects EQ back to initial movement of movement can be more less that Richter Scale this scale is not interpretated but rather measured Where do Earthquakes occur Seismic belts Earthquake depths shallow focus 20 Km intermediate 20 300 Km deep 300 Km Plate tectonic boundaries account for 95 of all quakes Zones of extremely deep sea Earthquakes Wadati Benioff zones Intraplate quakes only 5 of global EQs old structures respond to built up stress Earthquake damage intensity duration of vibrations surface waves R and L waves cause all the damage character of the substrate rock v fill proximity to the hypocenter frequency of earthquake waves cause ground acceleration g 10 20 g CLICKER Rayleigh and Love waves are both considered surface waves Building codes in developed countries strict codes in place to withstand large earthquakes buildings in Japan built for magnitude 10 Developing nations cant afford building codes The same magnitude quake would cause greater damge and more life loss in Pakistan than in San Francisco Landslides unstable slopes give way steepened from erosion or human activity Water expedites the process Liquefaction process where wet clay looses stickiness and turns into a slurry of mud and water without any strength Very similar to shaking yogurt Chapter 11 Mountains Faults Folds and Deformation Deformation occurs due to tectonic activity change in 1 Location 2 Orientation 3 Shape or volume due to applied stress Orientation measurement of orientation called dip tells how tilted rock is strike angle of imaginary horizontal line on a plane measured from north Dip maximum angle of a plane s slope For a Plane For a line Bearing compass angle of a line Plunge angle between line and horizontal Tilted sedimentary layers strike always perpendicular to the dip Some key terms Stress force per unit are acting on a rock to change shape and or volume strain change in shape or volume from stress Main kinds of stress Compression shortening Tension stretching shear moves sideways Deformation types Brittle material breaks discontinuous Ductile material flows w o breaks continuous Dependant on 1 temperature 2 pressure 3 deformation rate 4 composition Brittle vs Ductile deformation Ductile rocks do not break Brittle rocks break or fracture rocks do not all deform similarly Fractures part 1 Faults crack with relative movement recognized by offset displacement slip fault scarp drag folds fault breccia gouge slickenslides slip lineations Mylonite actually ductile but depends on T P and compostion Faulting is brittle and discontinuous in nature Offset same as displacement CLICKER wall that moves down hanging wall CLICKER faults are exps of Brittle deformation Folding ductile continuous deformation Produces synclines and anticlines Anticline makes an A arc Syncline sinful to face down If the strata become older towards the center of the structure then it s a dome If the strata become younger towards the center of the structure then it s a basin Mountain Building Active Mountain ranges mountain belt Linear range of mtns orogeny mountain building event processes that collectively produce a most mountain building at