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Hydrometeorological Hazards - Earthquake Hazards

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baejuhyeoned's version from 2017-03-09 18:38

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EarthquakesThe shaking or trembling caused by the sudden release of energy
EarthquakesUsually associated with faulting or breaking of rocks
(1) edge of the oceanic and continental plate, (2) Along faults: normal, reverse, transformWhere do earthquakes occur:
(1) Seismometers & (2) Seismographs2 ways to Measuring earthquakes
Seismometersinstruments that detect seismic waves
SeismographsRecord intensity, height and amplitude of seismic waves
Richter Scale Measures the energy released by fault movement
Richter Scalerelated to the maximum amplitude of the S wave measured from the seismogram
Richter ScaleLogarithmic-scale; quantitative measure
Richter ScaleFor each whole number there is a 31.5 times increase in energy
Richter ScaleMeasure magnitude
focus, or hypocenterThe point within Earth where faulting begins
epicenterThe point directly above the focus on the surface
Hypocenterlocation below the earth’s surface where the earthquake starts
Epicenterthe location directly above it on the surface of the earth
Foreshockssmaller earthquakes that happen in the same place as the larger earthquake that follows.
Mainshocklargest, main earthquake.
Aftershocksmaller earthquakes that occur afterwards in the same place as the mainshock.
(1) Ground Shaking, (2) Ground Rupture, (3) Liquefaction, (4) Earthquake-induced landslides (5) Tsunami5 Earthquake Hazards
Elastic Rebound TheoryExplains how energy is stored in rocks
Ground Shakingprimary cause of earthquake damage to man-made structures. When the ground shakes strongly, buildings can be damaged or destroyed and their occupants may be injured or killed.
S-waves (Shear Waves)Waves that move from side-to-side
S-waves (Shear Waves)slower than P-waves
S-waves (Shear Waves) particle motion in shear waves is perpendicular to the direction of the wave
S-waves (Shear Waves)move through solids
Surface WavesTravel just below or along the ground’s surface
Surface WavesSlower than body waves; rolling and side-to-side movement
P-waves (Primary Waves)first waves that the seismograph records.
P-waves (Primary Waves)"fast" wave , a push-pull or compressional wave, because it moves by contracting and expanding along a horizontal path
P-waves (Primary Waves) Propagate parallel to the direction in which the wave is moving
P-waves (Primary Waves) Move through solids, liquids
L-waves (Love waves)surface waves, which travel along the surface of the ground
L-waves (Love waves) slower than body waves—and more destructive
L-waves (Love waves)cause a horizontal shifting of the Earth perpendicular to the wave propagation.
L-waves (Love waves)Complex motion: Up-anddown and side-to-side
Rayleigh wavessinusoidal wave and move like ocean waves
Rayleigh wavesproduced by the interaction of P-waves and S-waves
Rayleigh wavesslowest of all the seismic waves with a speed approximately equal to 3 km/second
increasesVelocity _________ with rock density
changesVelocity __________ when passing from one material to another
Faster waves will travel the distance quicker and show up on the seismogram first.
Ground displacementt is how far the surface moves during the earthquake.
Ground velocityy is a measure of how quickly the ground was displaced – the speed and direction that the ground moved to get from its original location to its new location.
Ground accelerationis a measure of how quickly the ground changes velocity during the earthquake.
Effects of Ground Shaking Horizontal component of seismic wave motion most destructive
Effects of Ground ShakingCreates structural stress and primary way an earthquake affects buildings.
(1) the intensity of ground shaking caused by the quake coupled with, (2) the quality of the engineering of structures in the region. The two most important variables affecting earthquake damage
Ground shaking level of damage done to a structure depends on the amplitude and the duration of shaking
Ground shakingamplitudes are largest close to large earthquakes and the duration generally increases with the size of the earthquake
(1) Materials Matter, (2) Flexibility is Key, (3) Earthquake-Proof Foundations, (4) Earthquake Reinforcement, (5) Soil Types Can Limit DamageWhat can engineers do to prevent resonance and collapse of buildings?
Small, Wood-frame HouseSafest building
Most DangerousMost dangerous
Tuned mass dampersDevice that is built in large (several tons) mass that can sway at the top of the building in opposition to the building sway
Base isolationskyscrapers that float on systems of ball bearings, springs and padded cylinders.
Strong materials- high frequency (high velocity)REMEMBER
Weaker materials- low frequency (lower velocity)REMEMBER
Shear wave velocity increases as mean grain sizes increases however with higher frequency seismic wave amplitude will be lowerREMEMBER
Soil EffectsShaking is increased in soft, thick, wet soils. In certain soils the ground surface may settle or slide
Soil EffectsHard bedrock has higher frequencies softer sediments.
Soil Effects Fine grained sediments such as clay will experience greater shaking than coarse sediments such as sand
Consolidated sedimentssolid rock made from materials that have been metamorphosed or cemented together and sedimentary rocks
Consolidated sediments Ground water flows through fracture networks and/or pore space in these consolidated sediments.
Unconsolidated sedimentsloose materials, ranging from clay to sand to grave
Unconsolidated sedimentsGround water flows through spaces between the grains.
Unconsolidated sedimentsEarthquakes can liquefy this
memorize

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