EAPS 106 Exam 1
What drives plate tectonics?
Convection currents in the Earth's mantle drives plate tectonics
What is forecasting earthquake probabilities based on?
Forecasting earthquake probability is based on the history of earthquakes in the region.
How can GPS measures of surface deformation be used to predict how big the next
GPS measurements allow us to measure slip deficit rates, the amount an earthquake will need to slip in order to relieve elastic stress build up A slip deficit develops when plates move but a fault remains stuck Figure out how far the plates have to slip to relieve stress, and that corresponds to an estimated magnitude
Why did Italy recently send a seismologist to jail and that earthquake foreshocks are not a reliable precursor
Italy sent seismologists to jail for not predicting severity of the 2009 M6.3 L'Aquila earthquake based on foreshocks. More times than not, foreshocks do not occur before big earthquakes, so it's an unreliable precursor.
What are the largest earthquakes to have happened in the past 100 years?
Location Year M Duration Notes Chile 1960 9.5 11 min Tsunami hit Hwaii Alaska 1964 9.2 5 min Sumatra 2004 9.1 5 min Japan 2011 9.0 6 min Moved Japan ~ 5m Kamchatka 1952 9.0 4 min
What is the influence of loose sediments on earthquake shaking?
Loose sediments amplify the effects of earthquake shaking.
Whats is the average time between large earthquakes on the San Andreas Faults?
150 years
What is the approximate total number of earthquakes of any size that occur each year?
1.3 million
How many seismographs are required to locate an earthquake?
3 total 1 = distance, a giant circle where it could be 2 = intersecting circles, 2 potential locations 3 = exact location
What percent chance of avoiding collapse during an earthquake do California building codes require?
90% chance of survival, or 1 in 10 buildings will collapse
What is a supercontinent?
A supercontinent is many continents joined as one.
How do the largest earthquakes release more energy than the largest atomic bombs?
Amount of energy released by a M9 earthquake is equivalent to about 475 million tons of TNT; compared to the bomb dropped on Hiroshima equivalent to about 15,000 tons of TNT (source: US Geological Survey)
How do earthquake inertial damping systems work?
An earthquake inertial damping system is an approach to reducing the swaying of tall buildings during an earthquake, where the inertia of a suspended heavy mass counters earthquake shaking.
How do we know from the outer core of the Earth is liquid and the inner is solid
Beno Gutenberg discovered that shear waves were being blocked by something, turns out its the liquid outer core. There are zones of no S wave arrivals due to the core and also altering the path of the P waves.
Know that poorly constructed buildings often fall within seconds of the arrival of surface waves
Better but not great buildings can last 10 seconds
What is the relationship between earthquake magnitude and earthquake duration?
Bigger magnitude results in longer duration Magnitude Duration (sec) 4 - 4.9 1 - 5 5 - 5.9 5 - 15 6 - 6.9 15 - 30 7 - 7.9 30 - 50 8 - 8.9 50 - 120 9 - 9.5 120 - 650
What is the importance of proper foundations?
Buildings can fall over during an earthquake if not properly anchored to a strong foundation. The Space Needle is anchored by a strong foundation and not likely to fall over during an earthquake. - Its foundation is 30 ft deep, 120 ft across and was filled with 467 truck loads of steel reinforced concrete. - The space needle is bolted to its foundation with 72 bolts, each 30 feet long waves
How do you make a magnetic field generated by an electrical current stronger?
Coiling wire with an electric current increases the field strength, as well as replacing the center of the coil with a metal of some type like iron. The greater the current, the grater the magnetic field.
What are some consequences of losing our magnetic field?
Compasses would go crazy The auroras would be visible every night everywhere More charged particles would reach the Earth causing widespread power outages and broken satellites. Migratory animals that use the magnetic field (birds, turtles, bees, salmon) may have some difficulties. But no mass extinctions - we know this because the magnetic field has all but disappeared many times in Earth's past during magnetic reversals with no dire consequences
What are the basic processes of conduction, convection, and radiation?
Convection: Heat transfer through fluid motions of liquids and gases, as well as solids that flow like a fluid (which is referred to as solid state convection). Conduction: Heat transfer through a solid through the spread of vibrations on the atomic scale. Radiation: heat transfer through electromagnetic waves (light) through a transparent (clear) medium.
How do we know that our magnetic field has reversed itself many times?
Crystals in lava record the direction to the magnetic poles at the time of each eruption, There are also magnetic lineations on the seafloor that show new oceanic plates are created at mid ocean ridges, giving more evidence of continental drift. Black bands: normal magnetic field White bands: reversed magnetic field Big bands - no volcanic rocks to date
Why do diagonal beams help make a building more earthquake resistant?
Diagonal beams provide resistance to the shearing that often causes buildings to collapse. One beam gets compressed, and the other beam gets extended, helping to stop the motion (shearing / shaking) that affects buildings. Essentially, diagonal beams provide lateral stability for buildings.
How are earthquake magnitudes are related to the relative magnitude of shaking?
Each magnitude above is ten times stronger than one underneath it. So M6 is 10 times more than M5
What protects us from the solar wind?
Earth's magnetic field as well as the atmosphere, near the poles, protects us from the solar wind by stopping deady charged particles from the sun
What kind of magnetic pole is the Earth's north pole?
Earth's north pole is actually a magnetic south pole which was deemed based on geography before we knew better.
Why are earthquakes difficult to predict?
Earthquakes are hard to predict when they occur because earthquakes do not occur with any regularity, we can not directly or easily see faults beneath the earth, and the factors that control earthquake processes are chaotic. Note: We do know which faults are building up stress, but the above reasons make it difficult to know when they will slip
Where do most earthquakes occur?
Earthquakes primarily occur along plate boundaries where the crust is being torn apart to accommodate plate motions.
What can you do to minimize earthquake deaths, especially your own?
Educate the public about earthquake hazards, do not build near active faults, especially on loose soils or sediments, build earthquake resistant structures, develop; earthquake early warning systems. Stay indoors, drop to the ground, under a table, stay away from glass and anything that could fall, use a doorway for shelter only if you know it is a strongly supported load bearing doorway, do not use elevators. IF IN THIRD WORLD, GET OUTDOORS. If already outdoors anywhere, stay outdoors and away from buildings
What processes do elastic rebound and stick-slip behavior describe?
Elastic rebound is where the crust bends like rubber and stores energy, then unbends and releases the energy. Stick slip behavior is where faults remain stuck while energy builds, then suddenly slip when energy is released. Both processes occur at the same time to get an earthquake.
How does an overriding plate deform before compared to during a subduction zone earthquake
Elastically deforms before the subduction zone earthquake, and during the earthquake it releases the stored elastic energy (plate bounces back to where it was before)
Where is Hawaii located relative to plate boundaries?
Hawaii is located on the Pacific plate near the center which is far from the plate boundaries. Note: Volcanoes exist here because it's a hot spot not because of a plate boundary.
If you are inside a building during an earthquake, should you try to get out?
If not in a third world country then no but if yes then get outside asap
What is the relationship between the biggest magnitude earthquakes and the deadliest?
In general, the biggest earthquakes (M8+) aren't the deadliest. Usually the most deadly earthquakes are the M7+ that occur in heavily populated regions with poor building practices.
What is liquefaction?
Intense shaking during earthquakes that causes a near-surface layer of water-saturated sand to change rapidly from a solid to a liquid. Common in M 5.5 and greater earthquakes
How do we know the earth is not hollow?
Laboratory experiments show that rocks are too weak at high temperatures and pressures in Earth's interior to support voids. The passage of seismic waves shows no voids. The magnitude of our gravity requires a dense solid interior to our planet. There is no known physics to build a hollow planet with (or without) an impossibly tiny sun at its center. There is no net gravity inside a hollow sphere (equal pull in all directions) - everyone on the inside of a hollow Earth would drift around or fall into that central sun
What are the lithosphere and asthenosphere?
Lithosphere is a strong outer shell of the Earth consisting of the cold crust and uppermost mantle. The breaking of the lithosphere into pieces or "plates" and the manner in which they move around the surface of the Earth gives rise to the term "plate tectonics". The asthenosphere underlies the lithosphere and is hot enough to flow like a fluid (even though it remains a solid). It is the weakness of the asthenosphere that allows tectonic plates to slide around the surface of the Earth.
What is the theoretical maximum earthquake magnitude?
M10 is the theoretical max, which would require a fault that circles the Earth so it could never happen (it is the theoretical limit) M9.5 would likely be the largest that could occur
What does Mercalli intensity measure, the factors that influence it, and what does it enable us to infer?
Mercalli intensity quantifies the shaking that people and buildings feel and is influenced by the magnitude, distance, and the local geology. Mercalli intensities enable us to infer the magnitude of historic earthquakes and allows us to estimate how deadly an earthquake was likely to have been moments after it occurs.
What is a mid-ocean ridge, a subduction zone, and a transform plate boundary
Mid ocean ridges are places where magma comes up and forms new oceanic plates. They're referred to as divergent margins since the plates move away from each other. Subduction zones are the most important tectonic feature on Earth. Their relative motion gives rise to the highest mountains, the deepest valleys, the most active volcanoes, and the largest earthquakes. Oceanic plates get recycled back into the mantle at subduction zones, allowing continents to drift over the ocean basins. Subduction zones are referred to as convergent margins since the plates move toward each other. Transform plate boundaries are where two plates laterally slide past each other.
What evidence did Wegner use to suggest that the continents drift?
North and South America coastlines fit with Europe and Africa Identical volcanic flows appear on both sides of the Atlantic Fossils of non-swimmers found on both sides of the modern oceans
What is the problem with earthquake precursors?
Not all earthquakes have foreshocks and they don't occur reliably.
Which buildings were particularly sensitive to collapse during the 2008 Wenchuan, China earthquake?
Poorly built schools
What is asperity?
Rough spots along the fault are called asperities, basically rough surfaces that prevent the faults from moving until the asperity breaks.
How do earthquake early warning systems work?
Seismic waves travel slower than the speed of light (radio waves?). Therefore, one can detect an earthquake and communicate a warning ahead of the shaking (10 second warning)
What is solid state convection?
Solid-state convection is convection with a fluid that is in a solid state and not a liquid state or convection through a solid that flows like a liquid.
Know that there are unexplained phenomena like lights in the sky or strange animal behavior that have occurred before some earthquakes.
Some people in a specific village in China think that when the groundwater level changes, snakes emerge from their recently flooded dens, and the chickens flee to the roofs of structures to avoid the snakes.
What components are required for Earth's magnetic field?
The Liquid Outer Core provides all of the elements necessary. Electrical current comes from the motion of the electrical conducting liquid iron as the outer core convects, which is influenced by the spin of the planet The liquid iron acts as coils that spiral and increase the strength
What causes the aurora lights?
The aurora lights are caused by the deflection of the solar wind by the magnetic field which directs charged particles to our poles and excites the nitrogen and oxygen in the atmosphere causing the lights.
How did plate tectonics influence the evolution of whales and dolphins?
The evolution of dolphins and whales appears tied to the shallowing of the Tethys Sea when India collided into Asia.
Why is the outer core a liquid and the inner core a solid?
The outer layer is the only layer that remains hotter than its melting temperature. The inner core is at a higher temperature, but the melting temperature is also higher due to the greater pressure at the increased depth.
How did Earth acquire its internal heat?
The process of planet accretion results from lots of collisions, each producing heat. Combined with heat from the decay radioactive elements, the interiors of all new planets become so hot inside that they melt. Earth will never lose its heat prior to the Sun going Red Giant stage
How do earthquakes isolation systems work?
The swaying of buildings during an earthquake can be reduced by isolating a building from ground shaking. Buildings can be isolated from ground shaking by mounting them on isolators made of layers of steel and rubber that absorb the side-to-side motion caused by earthquakes. Pads of steel and rubber
True or False: You and your phone can be an earthquake early warning system.
True seismic waves travel slower than the speed of light/radio waves? (you can see an earthquake and communicate a warning ahead of the shaking)
Are their faults in Indiana?
There are old faults everywhere including Indiana. Most tend to be inactive though.
What was detected just prior to the 2004 Parkfield, Californian earthquake?
There was absolutely no surface motion
What do reflection and earthquake seismology allow us to visualize?
They allow us to visualize the underlying structure of the earth based on rocks with different densities causing differing refractions and reflections. Man made explosions allow visualizations of crystal structures at shallow depths. Observing how seismic waves from earthquakes travel through the Earth enables us to visualize deep structures such as subducting plates and the Earth's core
Why does the US Geological Survey believe there is a high seismic hazard in the midwest?
This is because there is an old rift zone where the reactivation of a 500 million year old ancient fault has occurred.
What settings (type of plate boundaries, direction of relative plate motion) do thrust, normal, and strike-slip faults occur?
Thrust faulting occurs in compressional settings like subduction zones, fault is at an angle so that slip along the fault enables the region to shorten, fault does not open during an earthquake, the two sides slide past each other while remaining in contact Normal faulting occurs in extensional settings like mid-ocean ridges, the fault is at an angle so that slip along the fault enables the region to lengthen, fault does not open during an earthquake, the two sides slide past each other while remaining in contact Strike slip faulting occurs in settings where plates slide laterally past each other, the fault is vertical (no headwall or footwall), the crust neither lengthens nor shortens, fault does not open during an earthquake, the two sides slide past each other while remaining in contact
Why don't faults open gaps in the ground when earthquakes occur?
Too much pressure on either side, can't open gaps. Always true for all 3 types of faulting.
What kind of plate boundary is the San Andreas Fault?
Transform plate boundary
What are the types of seismic waves and their basic properties?
Two types of seismic body waves: P waves and S waves, and two types of seismic surface waves: Love waves and Rayleigh waves. Seismic Body Waves: P waves (pressure wave) - Up-down/Push-pull motion (similar to sound wave), travels through solids, liquids, and gases, fastest seismic waves (first to arrive) but cause the least shaking S waves (secondary or shear) - back and forth/side to side motion, travel only through solids, slower than p waves (Second to arrive) but more shaking with them. Their energy is converted to P waves when they bounce off. Surface waves (arrives last, most damage, and travel along the surface of Earth): Love waves - have side to side motion, travel only along the surface of a solid, surface waves are the last to arrive, but cause the most deformation Rayleigh waves - have up-down motion like an ocean wave, travel only along the surface of a solid, last to arrive but cause most deformation
Know the time frame we can we reliably (90% confidence level) predict when and where an earthquake will occur.
We cannot reliably predict earthquakes. Several centuries?
How do we observe the buildup of stress on a fault?
We use several very precise GPS instruments, typically a station in the ground spread out over an area.
What is a passive plate margin?
When a boundary between continental crust and oceanic crust is not a plate boundary, it is referred to as a passive margin. Passive margins are the locations where a continent split into two and an oceanic plate grew between them as the two parts drifted away from each other.
Why is the interior of Earth layered?
When everything was melted, the dense elements like iron sank to the center forming an iron core, and the lighter elements like silicon and oxygen rise to form a rocky mantle and crust. Process is called differentiation. (spinning water bottle experiment)
What is forced resonance
When something excites the natural frequency inherent to a structure
Which Ridge occurred first? a) b) c)
a) (different picture, supposed to be the first one to arise)
If the inner core is hotter than the outer core, why is only the outer core a liquid? a) Because the inner core is at higher pressure than the outer core. b) Because the inner core is cooler than the outer Core c) Because the outer core has a higher melting temperature. d) Because the outer core is made of nickel while the inner core is made of iron.
a) Because the inner core is at higher pressure than the outer core.
How does heat transfer through Earth's mantle? a) Convection b) Conduction c) Radiation
a) Convection Since mantle flows like a fluid (solid-state convection)
What kind of fault separates the subducting Indio-Australian plate from the Eurasian plate? (Hint: this is a compressional setting) a) thrust b) normal c) strike-slip
a) thrust
Why does the U.S. Geological Survey believe that there is high seismic risk in our own backyard? a) because of modern earthquakes in the region b) because of the historic earthquakes in the region c) because there is plate boundary d) GPS observations show a fast buildup of stress in the region
b) because of the historic earthquakes in the region
Magnetic opposites attract, so does the south magnetic side of a compass point northward? a) yes b) no
b) no We designed our magnets/compasses to correspond to Earth's geographic poles
What kind of faults are these? (picture of rock ledge) a) thrust b) normal c) strike-slip
b) normal
What would be the immediate effect if the Earth lost its magnetic field? a) dogs and cats would start living together b) our electrical grid would have some major problems c) lightning strikes would greatly increase d) our planet would be "literally cooked" by microwave radiation
b) our electrical grid would have some major problems
What are earthquake forecasts based on? a) measurements of ground motion b) the history of earthquakes in the region c) current seismicity trends d) all of the above
b) the history of earthquakes in the region
Subduction of the Pacific Plate beneath Japan pushes Japan to the west between earthquakes. Which direction does Japan move when a subduction zone earthquake occurs? a) further west b) to the east c) Japan remains stationary while the Pacific Plate slides further beneath it
b) to the east It releases elastic energy
The difference between P and S wave arrival times can be used to locate an earthquake. How many seismograms are required to do this? a) 1 b) 2 c) 3 d) 4
c) 3
Which spaghetti/marshmallow structure will sway more when shaken? a) tall b) short c) both, it depends
c) both, it depends
The earth's four layers and their thicknesses
crust: radius = 6371 km, thiccness = 35 km mantle: radius = 6336 km, thiccness = 2850 km outer core: radius = 3486 km, thiccness = 2270 km inner core: radius = 1216 km, thiccness = 1216 km
What kind of seismic waves are these? (San Andreas clip) a) P-waves b) S-waves c) Love waves d) Rayleigh waves
d) Rayleigh waves
In general, in which time frame can we predict with 90% confidence that a large earthquake will occur on a particular fault? a) within several days b) within several years c) within several decades d) within several centuries
d) within several centuries
Which of the following has proven to be a reliable earthquake precursor? a) magnetic pulse rates b) foreshocks c) creeping surface motion near faults d) change sin groundwater levels e) there are no reliable earthquake precursors
e) there are no reliable earthquake precursors