Chapter 8

StudyBlue printing of Chapter 8 html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, font, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, b, u, i, center, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td { margin: 0; padding: 0; border: 0; outline: 0; font-size: 100%; background: transparent; } body { line-height: 1; } blockquote, q { quotes: none; } blockquote:before, blockquote:after, q:before, q:after { content: ''; content: none; } /* remember to define focus styles! */ :focus { outline: 0; } /* remember to highlight inserts somehow! */ ins { text-decoration: none; } del { text-decoration: line-through; } /* tables still need 'cellspacing="0"' in the markup */ table { border-collapse: collapse; border-spacing: 0; } /* end RESET */ .header { min-width:800px; } .logo { padding:6px 20px 2px 20px; margin:0; font-size:25px; font-weight:bold; color:#808285; position:relative; border-bottom: 1px solid #c5c5c5; } .logo-blue { color:#70adc4; } .logo-desc { font-weight:normal; font-size:19px; color:#cccccc; margin-top:50px; position:absolute; display: none; } .back-button { position:absolute; top:20px; right:20px; font-size:13px; line-height:25px; color:rgb(0,175,225); font-weight:normal; } .back-button a { color:rgb(0,175,225); } .instructions { padding:0; margin:0; width:100%; position:relative; color:rgb(100,100,100); } .step-holder { border-left:1px solid #ededed; margin-left:20px; } .steps { padding:15px 0; float:left; width:24%; border-right:1px solid #ededed; text-align:center; } .steps-01 { } .steps-02 { } .steps-03 { } .steps-04 { } .label { padding:5px 10px; } .print-button { } .print-button a { background-color:rgb(0,175,225); color:white; line-height: 19px; padding:9px 8px 5px 30px; font-size:14px; text-decoration:none; background-image: url(images/printer.png); background-repeat: no-repeat; background-position: 7px 50%; -moz-border-radius: 5px; -webkit-border-radius: 5px; } .print-button a:hover { background-color:black; } .theNote .content { width: 8.0in !important; margin: 5px auto; padding:20px; background-color:white; } .theNote .header { border-bottom: 1px dashed #C8C8C8; font-size: 17px; padding: 0 0 10px; line-height: 19px; color: #00ADE1; min-width:500px; } .theNote .body { font-size: 14px; line-height: 19px; padding: 10px 0; } .theNote{ padding:6px 0; clear:both; background-color: rgb(200,200,200); } .theNote h3{ color: rgb(100,100,100); } .theNote h1, .theNote h3{ background-color:white; padding:2px 20px; width:8.0in !important; margin: 0 auto; font-size: 15px; } .theNote h1{ padding-top: 10px; font-size: 15px; } .theNote h1:first-child{ font-size: 20px; } .theNote h3 { font-size: 14px; font-weight: normal; } #options { border: 3px double #ccc; padding: 5px 12px; margin: 10px 50px 10px 20px; float: left; } #info { border-top: 1px solid #ccc; padding-top: 5px; font-style: italic; } li { margin: 5px 10px 5px 25px; } ul li { list-style: disc; } ol li { list-style: decimal; } img { border: 0; } table { clear: both; width: 100%; border: 1px solid #c5c5c5; border-width: 1px 0; margin: 0; page-break-after: always; } table#page { page-break-after: auto; } td { text-align: center; font-size: 12px; border-bottom: 1px dashed #c5c5c5; height: 1.75in; width: 50%; padding-left: 15px; } .leftside { border-right: 1px solid #cccccc; padding: 0 15px 0 0; } .bottom td { border-bottom: none; } .clearfix { clear:both; line-height:1px; height:1px; } img { max-width:80%; max-height:150px; margin:20px; } @media print {.header { display: none; } .content .header{ display:inherit; } table { border: 1px dashed #bbb; border-width: 1px 0; } .theNote{ background-color:white; } } 8.1 - earthquake -vibration of Earth produced by the rapid release of energy -caused by slippage along a break in Earth's crust - focus -point within Earth where the earthquake starts - epicenter -location on the surface directly above the focus -usually associated with earthquakes -actual causes and effects of earthquakes were not understood before the 1906 San Fransisco earthquake -doe to this event western side of San Andreas Fault moved 4.7 meters to the North -forces within Earth slowly deform the crustal rocks on both sides -cause the rocks to bend and store elastic energy -rocks slip at the weakest point (the focus) -exerts forces farther along the fault -allows deformed rocks to snap back in place -this is an earthquake - elastic rebound -springing back of the rock to its original place - elastic rebound hypothesis - explanation for the release of energy stored in deformed rocks -most earthquakes are produced by the rapid release of elastic energy stored in rocks that has been subjected to great forces. when the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake -aftershocks -produced by movements that follow a major earthquake -usually weaker than main earthquake - foreshocks -small quakes that often come before a major earthquake -usually weaker than main earthquake - fault creep -slow gradual movement along the fault 8.2 Measuring Earthquakes -the first attempt to discover the direction of earthquakes was made by the Chinese - seismographs -instruments that record earthquake waves - seismogram -a trace produced by ground motion recorded by the seismograph - seismos: shake - gramma: what is written -show that 2 main types of seismic waves are produced by an earthquake 1) surface waves -seismic waves that travel along Earth's outer layer -movement similar to ocean waves -move in an up and down motion and side to side motion -side to side movement make surface waves the most destructive 2) Body Waves -travel through Earth's interior -identified as P or S waves -depending on how they travel through materials within Earth - P waves -push-pull waves -compress and expand rocks in direction waves travel -known as compression waves - S waves -shake particles at right angles to the waves direction of travel - transverse waves -temporarily change the shape of the medium - gas and liquids do not transmit S waves -a seismogram shows surface, P, and S waves -P waves are the fastest then S waves, then surface waves -differences in velocity used to locate epicenter -the direction of the epicenter can be know when a distance from 3 seismographs is known - 95% of the major earthquakes occur in a few narrow zones -most occur around the outer Pacific ocean -known as the circum-Pacific belt -some occur around the Mediterranean Sea - Mediterranean-Asian belt -others occur on a continuous belt through the worlds ocean - ocean ridge system -scientist have used 2 types of measurements to describe the size of an earthquake 1) intensity -measure of shaking at a given location based on the amount of damage -not a quantitative measurement 2) magnitudes -quantitative measurements -rely on calculations using seismograms -measure of the size of seismic waves or the amount of energy released at the source of the earthquake - richter scale -based on amplitude of the largest seismic wave - logarithmic scale -x10 increase in wave amplitude is an increase of 1 on the magnitude scale -only useful for small shallow earthquakes -moment magnitude scale -amount of displacement that occurs along a fault zone -calculated using several factors 1) average amount of movement along the fault 2) area of surface break 3) strength of broken rock - (surface area of fault) x (average displacement along fault) x (rigidity of rock) -moment magnitude is only scale that estimates the energy released by an earthquake 8.3 Destruction from Earthquakes -damage to buildings and other structures from earthquakes depend on several factors 1) intensity 2) duration of the vibrations 3) nature of the material structure is built on 4) design of the structure -unreinforced stone or brick buildings are the most serious safety threats - liquidification -occurs when loosely consolidated sediments are saturated with water -turns once stable soil into liquid - tsunamis -seismic sea waves -not produced by the tidal effect of the sun or moon -occurs where a slab of the ocean floor is is displaced vertically along a fault -can also occur when the vibration of a quake set an underwater landslide into motions -travels 500-950 km/hr -open ocean height less than 1 meter -wavelength: 100-700 km -in shallow water waves slow and can reach heights greater than 30 meters -water levels in tidal gauges can be used to determine if a tsunami has formed -with many earthquakes the greatest damage to structure is from landslides and ground subsidence or the sinking of the ground triggered by vibrations -violent shaking of earthquakes can cause landslides -can also cause large sections of ground to collapse, liquefy, of subside -fires can be started when gas and electric lines are cut - short range predictions -to provide an early warning of the location and magnitude of a major quake -monitoring of possible precursors 1) uplift 2) subsidence 3) strain of rock near active faults 4) water levels and pressures in wells 5) Radon gas emissions from fractures 6) small changes in electro magnetic properties of rocks -not successful so far - long range forecasts -give the probability of a certain magnitude earthquake occurring within 30-100 years -based on the idea that earthquakes are repetitive or cycling -only has limited success -not enough information about where and how earthquakes will occur in known to make accurate long term predictions seismic gaps -area along a fault where there has not been any earthquake activity for a long period of time 8.4 Earth's Layered Structure -deepest well is 12 km into earth's crust -If earth was made of the same materials throughout seismic was would travel in straight lines at a constant speed -there is an increase in the speed of waves with depth -due to pressure -changes the elastic properties of rock -paths of seismic waves are refracted as they travel -Earth's interior consists of 3 major zones based on chemical composition 1) crust 2) mantle 3) core - crust -thin, rocky outer layer of earth -divided into 2 parts 1) oceanic crust - 7 km thick -consists of igneous rocks basalt and gabbro -about 180 million or less years old -density: 3.0 g/cm 3 2) continental crust - 8-75 km thick -averages 40 km -consists of many rock types -average composition of continental rock is granitic rock called gandidiorite -average density of 2.7 g/cm 3 -some over 4 billion years old - mantle -contains over 82% of earth's volume -solid rocky shell -extends to a depth of 2890 km -dominant rock type in the upper mantle is peridotite -average density of 3.4 g/cm 3 -core -composed of iron-nickel alloy -average density of 13 g/cm 3 - temperature, pressure, and density are all directly proportional with depth -earth can be divided into layers based on physical properties 1) lithosphere 2) athenosphere 3) outer core 4) inner core -lithosphere -the crust and uppermost mantle -about 100 km thick - athenosphere -weak layer compared with the lithosphere -temperature and pressure results in a small amount of melting -part of upper mantle - outer core -liquid layer 2260 km thick -flow of metallic iron in this zone generates earth's magnetic field - inner core -sphere with a radius of 1220 km -compressed into a solid state - Andrija Mohorovicic -Croatian seismologist -in 1919 he presented evidence for layering in the earth -found that the velocity of seismic waves increases abruptly below 50 km - Mohorovicic discontinuity (Moho) -boundary separating crust from mantle -another boundary was discovered between mantle and outer core -seismic waves can travel around the world -p waves were bent around liquid outer core -caused P waves to arrive several minutes later than expected -region where bent P wave arrive is called the shadow zone -explained if core has a different composition than mantle - S waves cannot travel through the outer core -early seismic data and drilling technology indicate that the continental crust is mostly made of lighter granitic rocks -crust of the ocean floor has a basaltic composition -peridotite produces a substance similar to lava -meteorites are assumed to be composed of the original material from which Earth was formed -Earth's core thought to be mainly dense iron and nickel similar to metallic meteorites, the surrounding mantle is believed to be composed of rocks similar to stony meteorites