Earthquakes learning goals
Earthquakes learning goals Earthquakes: 1. Where do earthquakes happen worldwide? They happen near plate boundaries and intraplate. 2. How frequently do earthquakes happen? Earthquakes happen very frequently, small ones are very common and are often un felt while large ones are rare. 3. Types of tectonic plate boundaries Divergent play boundaries is where the plates move apart leading to tension from stretching and this causes smallish earthquakes, Convergent plate boundries, there are 2 kinds; subduction zone and continental collision. Continental collision is where continental plates collide and subduction zone is where the ocean subducts under a continental plate or another ocean plate. Also there are transform plate boundaries which are plates that move past each other resulting in a shearing motion. 4. Types of earthquakes that occur at these plate boundaries For convergent plate boundaries the earthquakes can be extensively small or very large. Subduction zones are where the largest earthquakes occur. For divergent plate boundaries only smallish earthquakes occur. Transform plate boundaries produce many earthquakes from their shearing motion they are moderate to large but not as big as convergent margins.
5. Describe how the Earth builds, stores, and releases energy in earthquakes (elastic rebound) The earth builds up energy as elastic stresses build up as rock deforms slightly overtime, the energy is stored as the elasticity of the fault strains and then the energy is released when the elastic stresses exceed what the fault can bear this causes rocks along fault to spring back to undeformed state which is known as elastic rebound. 6. Understand that stress causes strain, and differences between plastic, elastic, and brittle deformation Stress causes strain because the stress strains the fault to bend in one way or another, Plastic deformation is like putty it is where the material strains in response to stress but permanent also no energy is stored in plastic deformation and so it does not bounce back when the stress is removed. Elastic deformation has relatively small stress and because of these small stresses it is not permanent because the materials shape is restored when force is removed due to the stored energy and this released energy can pass as waves. In Brittle deformation the material does store elastic energy but at some point the material will break this results in catastrophic release of energy, Brittle deformation also includes repeated breaking of pre-existing weak surfaces (faults)
7. Describe how a fault slips in an earthquake and why shaking and damage are not always greatest at the epicenter Faults are weak surfaces (weaker than surrounding rock) they break repeatedly and may accumulate hundreds of km of slip over millions of years. Faulting occurs when the friction along he boundary line may temporarily slow down the rough lithospheric plates moving past each other and this braking action exerts forces on the rocks near the plate boundaries and as a result the rocks undergo strain or deformation and when the stress on them exceeds their breaking point the rock suddenly moves along a fault which is how a fault slip occurs. Shaking and damage are not always the greatest at the epicentre because when a rupture begins at the hypocenter and travels away, the rupture propagates away from the hypocenter at about 2-3 km/sec and shaking is greater in the direction the rupture travels.
8. Describe the different types of seismic waves and how they move through the Earth The 2 categories of seismic waves are body waves and surface waves. Body waves travel inside the earth while surface waves travel along boundaries between materials. There are 2 types of Body waves which are P and S waves. P waves move by compression and extension of the solid which is similar to a sound wave it is the fastest type of seismic wave and particles move the same way the wave propagates. S waves move by shearing distortion of the solid, Slower than P wave, it is about 3.5 km per sec as compared to the P waves 6km per sec. S waves also cannot pass through fluids while P waves can. Surface waves require an interface to move such as ground-air, water-air, mantle-liquid outer core. Surface waves are slower than body waves but cause more damage. The 2 types of surface waves are the Rayleigh wave which is a vertical and horizontal motion parallel to the wave direction (like an ocean wave) and then there is a Love wave which has horizontal movement perpendicular to wave travel direction. 9. Understand the principle behind early warning systems, and know how much warning time they can give. The principle behind early warning system is that through the use of S-P lag times and it would also be based on the principle that radio waves travel faster than seismic waves. It would work by having a network from of seismometers which would sense the first motion from a large earthquake which would then send a warning to the city and critical facilities the warning time would be from as short as 15 seconds to as long as 1 min 10. Describe how an earthquake is recorded and how we locate the epicenter An earthquake is recorded by a seismograph which analyzes its S-P lag time to figure out the distance of the epicenter of the earthquake from the seismograph. The exact epicenter can be located by using 3 or more seismographs at various locations that are apart from one another to triangulate where the epicenter is which works by creating a radius around each seismograph and the point where the 3 radii touch is where the epicentre is located. 11. Predict how local ground conditions will affect the duration and amplitude of shaking
Local ground conditions will affect the duration and amplitude of the shaking because if the local ground conditions are unconsolidated sediment or if the ground has high water content the seismic waves would slow which would cause some of the P and S Wave`s forward directed energy to be transferred to surface waves which would amplify the amount of ground motion because surface waves cause more shaking.
12. Compare and contrast the meanings and uses of magnitude and intensity scales Magnitude indicates how much energy was released and Intensity is how strong the ground motion is at the felt location. Magnitude scales indirectly estimate the magnitude they use seismic wave amplitude and distance to focus. Magnitude scales can find the Local magnitude, Surface wave magnitude or body wave magnitude. Intensity scales correlate with magnitude but they take into consideration bad construction and other earthquake effects such as landslides and fires. For earthquake intensity there are 4 major factors: Earthquake magnitude, ground type, distance from epicenter and duration of shaking which all contribute to how powerful the shaking will be this is scaled by the Modified Mercalli intensity 13. Explain the different magnitude scales, which one is best for large quakes, and why The Richter Magnitude is based upon the largest amplitude of shaking for high frequency body waves, (1Hz) it is Logarithmic like all earthquake scales. The Moment magnitude estimate is fundamentally different it is determined by an estimate of the area that ruptured along a fault plane during a quake and it is better for large quakes because shaking for large earthquakes is mainly low frequency so the Richer magnitude estimates for large quakes are too small 14. Explain factors that determine earthquake intensity Factors that affect intensity are Earthquake magnitude, Ground type, distance from epicenter and the duration of shaking. 15. Describe how local ground conditions can affect shaking Harder rocks (ex :North Van) result in no amplification and all frequencies are present. Softer rocks (ex: Richmond) result in a lot of amplification, loss of high frequency wave energy and reverberating low frequency waves. 16. Understand the basics of how buildings can be designed or retrofitted to better resist collapse or damage Base isolation can be used to let the ground move under the building, Dampers absorb energy in the building frame transmitted from the moving ground; a moment resisting frame can be used so the load is evenly distributed by making the connection between beams and column stronger.
17. Identify fault zones that could produce an earthquake damaging to Vancouver. Convergent Fault zone, North American plate and Juan de Fuca plate these 2 are part of a subduction zone. Cascadia Subduction and Queen Charlotte fault.
18. Explain what we can and cannot predict about large earthquakes Can predict where they will and the likelihood of them occurring but we cannot predict the exact time or location of earthquakes only estimate. 19. Explain the difference between forecasting and prediction Prediction specifies that an earthquake of a specific magnitude will occur in a defined region during a particular time period. Forecast: provides probability of the above usually over 10 to 100 year timescales.
KEY TERMS:
Body wave – a seismic wave that travels outward from the focus of an earthquake through the interior of earth Dip slip fault – Directivity- in the context of an earthquake, increased intensity of shaking in the direction of the fault rupture Earthquake- the sudden movement of rock on opposite sides of a fault; an earthquake releases strain that has accumulated within the rocks. Earthquake cycle- a hypothesis that explains successive earthquakes on a fault by a drop in elastic strain after an earthquake and the gradual accumulation of strain leading to the next quake. Epicenter-the point on earth’s surface directly above the source, or focus of an earthquake. Fault- a fracture along which adjacent rocks have moved relative to one another Focus- the point on a fault within earth where rocks first rupture during an earthquake; seismic energy radiates out from this point. Aka- hypocenter. Intensity- a measure of the severity of shaking and damage caused by an earthquake at a specific place. The modified Mercalli scale provides a numerical estimate of an earthquakes effects on people and structures. Interplate earthquake- an earthquake on a fault that bounds 2 lithosphere plates Intraplate earthquake- an earthquake on a fault in the interior of a continent, far from a plate boundary.
Liquefaction- the transformation of water saturated granular material from a solid state to a liquid state. Liquefaction commonly occurs during strong earthquakes. Magnitude- the amount of energy released during an earthquake. Material amplification- an increase in the intensity of earthquake ground shaking because of the type and thickness of geologic material through which the seismic waves pass. Modified Mercalli Intensity Scale- an earthquake intensity scale with 12 categories of ground shaking and structural damage Moment magnitude- a numerical measure of the amount of energy released by an earthquake. It is based on the seismic moment, which is defined as the product of the average amount of slope on the fault, the rupture area, and the shear modulus of the ruptured rocks. Normal fault- a fault along which hanging wall has moved down relative to the footwall. P wave- a seismic wave that travels from the hypocenter of an earthquake by compressing and extending rocks and fluids along its path. P waves are the fastest of all earthquake waves. Aka- primary or compressional waves. Paleoseismologists- a scientist who documents prehistoric earthquakes and deformation by studying young sediments, rocks, and landforms. Precursors- a physical, chemical, or biological phenomenon that immediately precedes an earthquake, volcanic eruption, landslide or other hazardous event. Reverse faults- a fault along which the hanging wall has moved upward relative to the footwall S wave- a seismic wave that travels in a snake-like fashion through solid material from the hypocenter of an earthquake. Aka- secondary or shear wave. Seismic wave-a wave produced by sudden displacement of rocks along a fault. Seismic waves move through or along the surface of earth. Seismograph- an instrument that records earthquakes Slow earthquake- a seismic event involving movement along a fault over a period of days to months- aka silent earthquake
Strike- slip faultSubduction zone- an elongate zone, typically hundreds to more than one thousand km long. Where two crustal plates converge, one moving slowly under the other. Subduction earthquake- an earthquake resulting from sudden slip along the a fault that separates two lithospheric plates at a subduction zone. The largest earthquakes on earth are subduction earthquakes. Surface wave- a seismic wave that travels along the ground surface. Surface waves are generally strongest close to the epicenter. ( cause structural damage) Tectonic creep- the slow, continuous movement of rock or sediment along a fracture Also called tectonic creep. Thrust fault- a low-angle reverse fault along which older rocks are displaced over younger rocks.
5. Describe how the Earth builds, stores, and releases energy in earthquakes (elastic rebound) The earth builds up energy as elastic stresses build up as rock deforms slightly overtime, the energy is stored as the elasticity of the fault strains and then the energy is released when the elastic stresses exceed what the fault can bear this causes rocks along fault to spring back to undeformed state which is known as elastic rebound. 6. Understand that stress causes strain, and differences between plastic, elastic, and brittle deformation Stress causes strain because the stress strains the fault to bend in one way or another, Plastic deformation is like putty it is where the material strains in response to stress but permanent also no energy is stored in plastic deformation and so it does not bounce back when the stress is removed. Elastic deformation has relatively small stress and because of these small stresses it is not permanent because the materials shape is restored when force is removed due to the stored energy and this released energy can pass as waves. In Brittle deformation the material does store elastic energy but at some point the material will break this results in catastrophic release of energy, Brittle deformation also includes repeated breaking of pre-existing weak surfaces (faults)
7. Describe how a fault slips in an earthquake and why shaking and damage are not always greatest at the epicenter Faults are weak surfaces (weaker than surrounding rock) they break repeatedly and may accumulate hundreds of km of slip over millions of years. Faulting occurs when the friction along he boundary line may temporarily slow down the rough lithospheric plates moving past each other and this braking action exerts forces on the rocks near the plate boundaries and as a result the rocks undergo strain or deformation and when the stress on them exceeds their breaking point the rock suddenly moves along a fault which is how a fault slip occurs. Shaking and damage are not always the greatest at the epicentre because when a rupture begins at the hypocenter and travels away, the rupture propagates away from the hypocenter at about 2-3 km/sec and shaking is greater in the direction the rupture travels.
8. Describe the different types of seismic waves and how they move through the Earth The 2 categories of seismic waves are body waves and surface waves. Body waves travel inside the earth while surface waves travel along boundaries between materials. There are 2 types of Body waves which are P and S waves. P waves move by compression and extension of the solid which is similar to a sound wave it is the fastest type of seismic wave and particles move the same way the wave propagates. S waves move by shearing distortion of the solid, Slower than P wave, it is about 3.5 km per sec as compared to the P waves 6km per sec. S waves also cannot pass through fluids while P waves can. Surface waves require an interface to move such as ground-air, water-air, mantle-liquid outer core. Surface waves are slower than body waves but cause more damage. The 2 types of surface waves are the Rayleigh wave which is a vertical and horizontal motion parallel to the wave direction (like an ocean wave) and then there is a Love wave which has horizontal movement perpendicular to wave travel direction. 9. Understand the principle behind early warning systems, and know how much warning time they can give. The principle behind early warning system is that through the use of S-P lag times and it would also be based on the principle that radio waves travel faster than seismic waves. It would work by having a network from of seismometers which would sense the first motion from a large earthquake which would then send a warning to the city and critical facilities the warning time would be from as short as 15 seconds to as long as 1 min 10. Describe how an earthquake is recorded and how we locate the epicenter An earthquake is recorded by a seismograph which analyzes its S-P lag time to figure out the distance of the epicenter of the earthquake from the seismograph. The exact epicenter can be located by using 3 or more seismographs at various locations that are apart from one another to triangulate where the epicenter is which works by creating a radius around each seismograph and the point where the 3 radii touch is where the epicentre is located. 11. Predict how local ground conditions will affect the duration and amplitude of shaking
Local ground conditions will affect the duration and amplitude of the shaking because if the local ground conditions are unconsolidated sediment or if the ground has high water content the seismic waves would slow which would cause some of the P and S Wave`s forward directed energy to be transferred to surface waves which would amplify the amount of ground motion because surface waves cause more shaking.
12. Compare and contrast the meanings and uses of magnitude and intensity scales Magnitude indicates how much energy was released and Intensity is how strong the ground motion is at the felt location. Magnitude scales indirectly estimate the magnitude they use seismic wave amplitude and distance to focus. Magnitude scales can find the Local magnitude, Surface wave magnitude or body wave magnitude. Intensity scales correlate with magnitude but they take into consideration bad construction and other earthquake effects such as landslides and fires. For earthquake intensity there are 4 major factors: Earthquake magnitude, ground type, distance from epicenter and duration of shaking which all contribute to how powerful the shaking will be this is scaled by the Modified Mercalli intensity 13. Explain the different magnitude scales, which one is best for large quakes, and why The Richter Magnitude is based upon the largest amplitude of shaking for high frequency body waves, (1Hz) it is Logarithmic like all earthquake scales. The Moment magnitude estimate is fundamentally different it is determined by an estimate of the area that ruptured along a fault plane during a quake and it is better for large quakes because shaking for large earthquakes is mainly low frequency so the Richer magnitude estimates for large quakes are too small 14. Explain factors that determine earthquake intensity Factors that affect intensity are Earthquake magnitude, Ground type, distance from epicenter and the duration of shaking. 15. Describe how local ground conditions can affect shaking Harder rocks (ex :North Van) result in no amplification and all frequencies are present. Softer rocks (ex: Richmond) result in a lot of amplification, loss of high frequency wave energy and reverberating low frequency waves. 16. Understand the basics of how buildings can be designed or retrofitted to better resist collapse or damage Base isolation can be used to let the ground move under the building, Dampers absorb energy in the building frame transmitted from the moving ground; a moment resisting frame can be used so the load is evenly distributed by making the connection between beams and column stronger.
17. Identify fault zones that could produce an earthquake damaging to Vancouver. Convergent Fault zone, North American plate and Juan de Fuca plate these 2 are part of a subduction zone. Cascadia Subduction and Queen Charlotte fault.
18. Explain what we can and cannot predict about large earthquakes Can predict where they will and the likelihood of them occurring but we cannot predict the exact time or location of earthquakes only estimate. 19. Explain the difference between forecasting and prediction Prediction specifies that an earthquake of a specific magnitude will occur in a defined region during a particular time period. Forecast: provides probability of the above usually over 10 to 100 year timescales.
KEY TERMS:
Body wave – a seismic wave that travels outward from the focus of an earthquake through the interior of earth Dip slip fault – Directivity- in the context of an earthquake, increased intensity of shaking in the direction of the fault rupture Earthquake- the sudden movement of rock on opposite sides of a fault; an earthquake releases strain that has accumulated within the rocks. Earthquake cycle- a hypothesis that explains successive earthquakes on a fault by a drop in elastic strain after an earthquake and the gradual accumulation of strain leading to the next quake. Epicenter-the point on earth’s surface directly above the source, or focus of an earthquake. Fault- a fracture along which adjacent rocks have moved relative to one another Focus- the point on a fault within earth where rocks first rupture during an earthquake; seismic energy radiates out from this point. Aka- hypocenter. Intensity- a measure of the severity of shaking and damage caused by an earthquake at a specific place. The modified Mercalli scale provides a numerical estimate of an earthquakes effects on people and structures. Interplate earthquake- an earthquake on a fault that bounds 2 lithosphere plates Intraplate earthquake- an earthquake on a fault in the interior of a continent, far from a plate boundary.
Liquefaction- the transformation of water saturated granular material from a solid state to a liquid state. Liquefaction commonly occurs during strong earthquakes. Magnitude- the amount of energy released during an earthquake. Material amplification- an increase in the intensity of earthquake ground shaking because of the type and thickness of geologic material through which the seismic waves pass. Modified Mercalli Intensity Scale- an earthquake intensity scale with 12 categories of ground shaking and structural damage Moment magnitude- a numerical measure of the amount of energy released by an earthquake. It is based on the seismic moment, which is defined as the product of the average amount of slope on the fault, the rupture area, and the shear modulus of the ruptured rocks. Normal fault- a fault along which hanging wall has moved down relative to the footwall. P wave- a seismic wave that travels from the hypocenter of an earthquake by compressing and extending rocks and fluids along its path. P waves are the fastest of all earthquake waves. Aka- primary or compressional waves. Paleoseismologists- a scientist who documents prehistoric earthquakes and deformation by studying young sediments, rocks, and landforms. Precursors- a physical, chemical, or biological phenomenon that immediately precedes an earthquake, volcanic eruption, landslide or other hazardous event. Reverse faults- a fault along which the hanging wall has moved upward relative to the footwall S wave- a seismic wave that travels in a snake-like fashion through solid material from the hypocenter of an earthquake. Aka- secondary or shear wave. Seismic wave-a wave produced by sudden displacement of rocks along a fault. Seismic waves move through or along the surface of earth. Seismograph- an instrument that records earthquakes Slow earthquake- a seismic event involving movement along a fault over a period of days to months- aka silent earthquake
Strike- slip faultSubduction zone- an elongate zone, typically hundreds to more than one thousand km long. Where two crustal plates converge, one moving slowly under the other. Subduction earthquake- an earthquake resulting from sudden slip along the a fault that separates two lithospheric plates at a subduction zone. The largest earthquakes on earth are subduction earthquakes. Surface wave- a seismic wave that travels along the ground surface. Surface waves are generally strongest close to the epicenter. ( cause structural damage) Tectonic creep- the slow, continuous movement of rock or sediment along a fracture Also called tectonic creep. Thrust fault- a low-angle reverse fault along which older rocks are displaced over younger rocks.
