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Earthquakes
E&S 8
| Question | Answer |
|---|---|
| Earth's radius | 6370 km |
| average depth of ocean | 4 km (70%) |
| continent's average elevation | 840 m above sea level |
| what are the layer of the earth? (outer to inner) | crust, mantle, outer core, inner core |
| which layer is the only one that is liquid and NOT solid rock? | outer core |
| alfred wegener | noticed continents matched like a puzzle, found fossils on different continents; suggested continental drift theory |
| Sir Harold Jeffreys | objected Wegener's theory and stalled the study of plate tetonics for forty years |
| Emile Argand | used to study medicine then switched to geology; agreed with Wagener; amplified plate tetonics theory and theory of evolution; examined sediment placement |
| Arthur Holmes | proposed that rocks flow because they are heated from below and cooled from above; silly putty example (pull fast |
| how slow do rocks flow? | mantle rocks flow a few cm a year; takes around 100 million years to flow from top to bottom of mantle |
| age of earth | 4.6 billion |
| oldest rocks | 4.2 billion |
| most forms of life started to appear | around 500 million years ago |
| oldest oceanic seafloor today | 200 million years |
| convection | flow driven by heating; heat from below and cool from top; top sinks, bottom rises; liquid continually overturns |
| harry hess | discovered midocean ridges, proposed sea floor spreading |
| earth's magnetic field | switches sign randomly every .5 |
| how fast do tetonic plates move? | 0 to 20 cm/year; 25 miles per million years |
| number of plates | 10 |
| pangaea | around 350 to 175 million years ago all continents were connected, NA on equator and dinosaurs ruled to earth |
| supercontinent progression (youngest first) | Gondwanaland, Pangeae, Rodinia, Columbo, Kenorland, Ur, Vaalbara (God, Please Reserve, Can Keep U Virginal) |
| Wilson Cycle | the openning and closing of the ocean floor, seafloor younger than continental crust |
| crust types | ocean: 8km; continents: 30 km, floats on mantle |
| types of plate boundaries | divergent, convergent, transform |
| divergent plates | plates move away from each other, mantle rises to fill the space; midocean ridges, rift in contintental plate |
| convergent plates | plates move toward each other, one gets pushed down while the other gets pushed up, subduction zones |
| transform plates | rub against each other, no land is created or destroyed |
| subduction zones | large and frequent earthquakes, crust is destroyed, earthquakes occur at surface to 700 km below |
| 3 types of subduction | ocean to ocean (trenches are deepest in ocean), ocean to continent (active volcanism), continent to continent (makes mountains because it does not subduct |
| faults | can be active or inactive, can be seismic or aseismic |
| trust v normal faults | in thrust, hanging wall move up; in normal, footwall moves up |
| 3 exceptions for most quakes occuring at plate boundaries | mid continental quakes, hotspots, blurring at plate boundaries |
| ductile v brittle | ductile is slow, everyday plate movement while brittle is fragil rock with fast motion that can be found around the time of earthquakes |
| earthquake occurance formula | slip in earthquakes=fault rate x time between quakes |
| why you can't count on a formula | little earthquakes take some of the slip, earthquakes trigger others to occur before they are due, calculation most useful as a "warning" |
| stress | force per unit area |
| strain | the fraction of size that a body is destroyed |
| linear elasticity | when stress is proportional to strain |
| friction increases with | depth; pressure grows, more strain accumulated, deep quakes release a lot more stress |
| fault trace | where fault plane intersects the Earth's surface |
| fault scarp | steep slope formed by fault motion, erosion smoves scarps with time, it sticks up like a ledge |
| rupture process | rock breaks and slides against each other, sliding rocks send vibrations outward, most of damage in quakes is caused by vibrations |
| focus | point where the rupture started |
| hypocenter | location and time of start of quake |
| epicenter | surface projection of hypocenter |
| rupture | the breaking of rocks and sliding of one side of the fault against the other side, occurs when stress exceeds strength |
| crack speed after rupture | 3 km/sec |
| crack lenghth | larger length means greater magnitude and longer duration |
| magnitude and approximate rupture sizes | Mag 8: 500 km; Mag 7: 70 km; Mag 6: 10 km; Mag 4: 200m; Mag 2: 5m |
| wave | disturbance that travels far through a medium |
| seismic waves | vibrations of the ground, elastic waves |
| raypaths and wavefronts | raypaths are lines that show the direction that the seismic wave is propagating; wavefronts connect positions of the seismic wave that are doing the same thing at the same time; raypaths are generally perpendicular to wavefronts |
| amplitude | the max wave height, high amplitude=high sound |
| wavelength | horizontal length of one cycle of a wave |
| period | the time required for one wavelength |
| frequency | number of waves that pass a certain poin in a given amount of time |
| velocity | rate at which the wave travels; V=wavelength/period=wavelength X frequency |
| 3 kinds of elastic waves | longitudinal, horizontal transverse, vertical transverse |
| types of seismic waves | Body waves (P and S), Surface waves (Love and Raleigh) |
| P Waves | longitudinal, material moves back and forth in the direction the wave travels, fastest type of wave, 5 |
| S Waves | material moves back and forth perpendicular to wave direction, arrives second to P wave, 3 |
| surface waves | travel on surface of earth, slower than S waves, largest amplitude; Love waves go side to side, Raleigh waves go up and down |
| formula to measure distance from EQ | (Difference in time of P and S waves)/[(1/Velocity S) -(1/Velocity P)] |
| complications for seismic waves | reflection, refraction, conversion |
| measuring stress and strain in nature | stress cannot be determined so we look to measure strain (deformation) |
| seisometer | instrument that record the motions in the ground |
| mass spring seismometer | requires one part to be attached to the ground and another to be isolated from the ground, requires a spring to return mass to original position and a damping mechanism to stop mass from moving and affecting future recordings, and also a pivot so mass mov |
| types of seismometers | mass/spring, challenger space study, remote locations |
| magnitude | measures the size of the earthquake |
| intensity | Measures the effect of an earthquake at a location; Scale from 1 to 12; Obtained from damage to buildings, changes in the earth's surface, felt reports; useful for historic earthquakes and comparing today's to past |
| measures of an earthquake | magnitude, intensity, length of fault that breaks, area of fault break, displacement, seismin moment (area X displacement), death or injuries, damage ($) |
| earthquake effects | ground shaking, ground settling, landslide & avalanches, fault offset, tsunamis & seiches |
| human assisted hazards from a quake | fires, flood from dam failure, toxic spills |
| ways of measuring an earthquake | felt reports (not very accurate), seismic measurements, mapping of rupture zone, Geodetic measurements of ground shift, Geologic observations of past earthquakes (fault displacements) |
| magnitude | measure of the earthquake's size; Determined by taking the logarithm of the largest ground motion recorded form a particular wave type, correction for distance from seismometer to epicenter; Several types depending on wave |
| Charles Francis Richter | made Ritcher scale in 1935, nudist, help telephone, no grad student, had seismometer on his coffee table |
| Richter magnitude | M=log(10)A where A is the amplitude on the instrument; Ex: M=log(1mm)=3, M=log(1000mm)=6 |
| different types of magnitudes | M(L): local or Richter mag, uses S wave; M(B): body wave magnitude, P wave at 30 to 90 degrees; M(S): surface wave mag; M(W): moment magnitude, uses seismic moment |
| how large can earthquakes get? | in 1960 Chile recorded M(W) 9.5, but we have only been recording for 50 years; the whole earth breaking in half M(W) 12; subduction quakes hit 9; transform and ridge quakes hit 8 |
| seismic moment | M(O)=mui*Distance*S(surface area ruptured) N.m |
| moment magnitude | M(W)=2/3log(M(O))-6 |
| rule of thumb on magnitudes | a quake X+1 has 10 times greater amplitude, 3.3 times longer length and duration, 33 times greater energy in waves at release time |
| explosions | first motions are all compressive in all directions, this is how you can tell it is different from an earthquake |
| how many earthquakes are there in a year? | 15 w/ mag>7, 155 w/ mag>6, 1300 w/ mag>5, 10,000 w/ mag>4, linear relationship, about 20,000 a year w/ mag>1 |
| Gutenberg/Richter relationship | equation for # of quakes; Log N=a |
| earthquake regular occurance | a little less than one mag 3 per week, but most can't even be felt |
| seqence | set of quakes that appear related in space and time |
| foreshock | quake followed by a bigger quake, can occur hours before, only half of mainshock have foreshocks, near mainshock hypocenter |
| mainshock | biggest quake in a sequence; larger mainshocks have more aftershocks, foreshocks and aftershocks usually mag or more smaller than mainshock |
| aftershock | quake after the biggest quake in a sequence; Near mainshock rupture zone; Can number in thousands; Can go on for years or decades; Most predictable and studied quakes |
| corollaries | one never knows that a quake is a foreshock until the bigger mainshock coems along; Aftershocks can turn into foreshocks |
| differences between mainshocks and aftershocks | none, they are all earthquakes that just occur at different times in the sequence |
| Omori's Law | number of aftershocks decreases with time, N=C/t; and the likelihood of having big quakes decreases too |
| non conventional sequences | swarms. long range triggering, jumping faults |
| swarms | most common in volcanic areas, no obvious mainshock |
| Alaska | subduction thrust plate boundary, most dangerous faults in US with 8 eq > M=8 in last 100 years; Queen Charlotte fault |
| Diblee Maps | mapped CA on foot, wrote paper proposing lateral displacement along SA fault by 250 km |
| Eastern CA Shear Zone | 3 largest earthquakes in 140 years |
| Wasatch | Nevada, Utah, Idaho, Montana, Wyoming; 10 |
| Why is an earthquake famous? | remarkable by size, destruction, particular setting; proximity |
| How earthquakes damage trees | beheading, cutting roots |
| December 1812 | bad year for missions, two quakes, learned trees could be a good source about quakes when historical info is short, large quakes can cause damage far from fault |
| 1971 Sylmar quake | structures are damaged not only by how hard you shake but also by how long, dams subject to liquefaction |
| 1994 Northridge quake | buried fault=blind fault |
| 1984 Loma Prieta quake | liquefaction dangerous in artificial landfills, shaking amplified by soft soil |
| 1946 Alaska quake/tsunami | waves reached HI, Santa Cruz, Chile; in deep water, waves travel as fast as jets (800 km/hr) |
| tsunami | an ocan wave caused by motion of seafloor in quake, volcanic eruption or landslide; bigger wave created in deeper water; slow down in shallow water but have greater height |
| Chile 1960 | largest earthquake in the world |
| 1995 Kobe, Japan | costliest earthquake in history, compareable magnitude to Northridge but did more damage |
| 1556 Shaanix, China earthquake | deadliest quake ever, 0.83 million |
| 1975 Haicheng, China | thought they could predict earthquakes, but then 14 months later there was the worst disaster of the 20th century |
| Turkey | like California in that there are strike slip quakes, had a series of quakes in the 1940s |
| 2004 Sumatra Andaman earthquake | M9.0, 3rd largest ever, along subduction of IndoAustralian plate under Indonesia and the Berma plate, earth's rotation actually sped up and shortened the day |
| by 2.8 microseconds, no way to get warning to coastline communities | (blank) |
| Human factors that worsened the 2004 Sumatra quake | destruction of coral reefs, coastal mangrove forests and natural sad dunes |
| Lessons learned from earthquakes | (1)large EQ have large rupture area (2)can occur in unexpected places (3)exposed fault not an indicator size (4)EQs interact and sometimes progress along faults (5)people density & building practices determine # deaths (6)2ndary effects can be worse |
| Avoid living on fault | could be used for parks or streets; try to live at least 5 miles from a fault |
| Hazards due to ecological conditions (site) | soft soil increases shaking, wet soil liquefaction or landslides, cliffs and ridges are prone to landslides |
| Soft sites | stronger shaking, seismic waves grow in amplitude when passing from rock to softer material, uneven settlement |
| liquefaction | heavy solid objects (houses) will sink while hollow objects (septic tank) will float |
| cliffs and ridges | experience greater shaking because of wave reflection in concentrated area; landlisde and rockfall potential |
| Three basic considerations in building | (1) materials (2) design (3) quality of execution |
| Types of lateral bracing | diagonal, shear-wall, and frame-action |
| Soft story | openings present on first floor of building that reduce the strength of the wall; garage, doors, windows |
| wood frame with stucco | bad, adds weight and makes buildling weaker, can fall off, 1" of stucco=1/4" plywood |
| Earthquake preparedness | 60% chance most people will be at home in the event of a quake |
| common hazzards | furniture, pictures on walls, items falling on beds |
| To make an earthquake prediction, you need to state | (1) time interval it will occur (2) region it will be (3) projected magnitude |
| possible (false) EQ precursors | (1)increase or decrease in # of EQs (2)slow round motion (3)random emission (4)electrical resistivity (4)electromagnetic field (5)water chemistry (6)seismic wave velocity |
| problems with false alarms | expensive, disruptive, make people less likely to respond |
| hazard and risk | hazard is probability that an area will be affected; risk is probability that loss will occur; preparation lowers risk, not hazard; Risk=hazard*vulnerability*value |
Created by:
katydid
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