1、Earthquakes,珍烧醚淬尘穴箱听惩坍仁戍献人纳宝徐脆饰藉愿玩守几奔祟递较册析余高Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),What is an earthquake?,An event that releases stored energy in the earths crustTakes place along a fault planeCan be naturally-occurring or human-induced (e.g. explosives used in mining)Large enough eart
2、hquakes manifest themselves on the surface of the earth through shaking and other ground displacement,魂蝴龋劫迭沽眺捍幻赖蔚员纶赛蜕逊波卖嚼伞吱税俐袭涝梢糊鸳药摸缆毅Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Earthquake Distribution,怠慧屡御推灌盆瓮刑撇薪爪赌胺演勤更捌吮耍梳像头弄饥氟嗅燥倍篓拒敞Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),What
3、 causes earthquakes?,As we know, the Earths lithosphere is divided into plates that interact with each otherAny gradual build up of stress due to the movement of plates can eventually be released as energy when the rocks that are stressed finally break,卤薪型簇造磋掩怀型都炯孕鞍厌共级汝泥攘熙枯纸祥搁折寓侣颖航驾缮句Lecture_10(Eart
4、hquakes)(1)Lecture_10(Earthquakes)(1),Elastic Rebound Theory,Describes the sudden release of the accumulation of stress causing movement along a faultNew fault or existing faultRequires that rock is somewhat ductileIt can bend without breakingRemember stress vs. strain (Lecture 3)The deeper the rock
5、 in question, the more ductile it iswarmerRock that is deep enough to undergo plastic deformation will not generate earthquakes,敬棺配愧绽吹瑞剧虎黄酒园象寥词帘石躺拟稽算耪络曰统堪盒贮花限湖有Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Types of Faults(Review from Lecture 3),There are three main categories of faultsNormal
6、faultReverse faultThrust fault is a type of reverse faultStrike-slip faultTransform fault is a type of strike-slip fault,熊抡兔宪弦墨默鉴养疹螺幸膊咎特胜卿鲍宵均乖痘缝荐匝股毯劝绪恼熬猿Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Normal Fault,Not very common, despite the nameOne land mass moves away from another with gravi
7、tyForms fault scarps,Fault scarp,姨碾炒厄讫趋靡竟姨瞥径骄呆获蚂征甥零灰砚久义酸始品擞武眼荡顺越篱Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Reverse Fault,Occurs where one land mass is pushed upwards against another land massIf the angle of contact is less than 45, it is called a thrust fault,边谎摧卓神妖沮惹羹欢辞饿奠千衍惜蜘耍刊辐毫增羽貉呛佐氨受哪
8、考谗摸Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Strike-slip Fault,Occurs at transform marginsOne land mass slides past another one with negligible vertical motion,查昂再唉下骤姆被僻轮署彪力蘑熙依阴勋腰渠壶缔铬岛将威柳蕉潭羊场霍Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Transform Fault,A type of strike-slip fault
9、with abrupt terminationsOccurs at spreading centersMagma intrusion forces apart two lithospheric plates, but the motion is not smoothPlates spread through abrupt breakage of oceanic crustal materialBreakage causes moderate earthquakes,USGS,密再励轮挛煎膛窃苑兽厄喻期抠典怨筛吨仔胰时柠哨爬杉震杰哇威彪篷羚Lecture_10(Earthquakes)(1)Le
10、cture_10(Earthquakes)(1),Horsts and Grabens,A graben is an area bounded by two parallel normal faultsA horst is the piece of land that remains stationary whilst the graben is formed,USGS,匹乘涪破扛褒进基肠逐惜政脑瑶莽屿烷恐魔篡驮篓设喉霜涛幼孜氮锗氛跃Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Types of Waves,Earthquakes g
11、enerateBody waves (travel through the earth)P and S wavesSurface waves (travel along the surface)Rayleigh and Love waves,曾扑跌关涂剔伊衰庄锁焙援锋凳咱锑肖视匪俄朱六辖代挎双贱萝吧号详爽Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Body Waves,P-waves (compressional or primary)Moves 4-7 km/secPrimary wave to be detected at a
12、recording stationRock vibrates parallel to the direction of wave propagationCan pass through liquid or solid materialAre refracted when they change media,Purdue,趣秧睡矣膀指腰爵炔脖肇抉洽溺疯氨唇肩戮憾耶词壮膝衬馅绦罚它贯色礁Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Body Waves,S-waves (shear or secondary)Moves 2-5 km/se
13、cSecond wave to be detected at a recording stationRock vibrates perpendicular to the direction of wave propagationCan only pass through solid material,Purdue,谊狄少澜诊茧明夷柑熟着论导蚕持氰橡谴澈牢滞属改盆答虏猎菏叫缆坯姑Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Surface Waves,Rayleigh wavesBehave like ocean wavesDestru
14、ctiveCause much land movementSlow-movingLove wavesLike S-waves with no vertical movementGround movement is perpendicular to propagation directionDestructiveCause side-to-side swinging of buildings,Plummer et al.,涸败歼机膊蜒椭梨徒慷磁几钳又谣芝菇赊况了蒲倒惕惕尺鹊毗厚圭舶襄场Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Mea
15、suring Earthquakes,SeismometerVarious designs, depending on the type of motion you wish to observeE.g. (right). The weight stays stationary due to inertiaDrum turns constantlymoves left, drawing a line moving to the right, moves right, and line goes left,,厚董百讲划脏决漳兜累掐圃埔侍舆滓伍教耐汾佑开遵德场赚矫焙慧俏镇卉Lecture_10(E
16、arthquakes)(1)Lecture_10(Earthquakes)(1),Locating Earthquakes,There is a global network of seismometersEven a small earthquake is possible to detect from far awayWith a sensitive seismometerIt is possible to tell how far away an earthquake occurredFrom the difference in arrival time of P- and S-wave
17、s,龟荷砧攫银素亥蓬芦么铃母遍累液暑连兵煤欣婚举歼瘸付踢呼菩孩堪芥渍Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Seismograms,A seismogram is the graphical representation of Earth movement,USGS,沦政桂嫩便倘朱捣偿显道周材头躺谁半酣日阁认仗导撑绎吓巨冬山镇椿再Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Not necessary to know what type of rock waves tr
18、aveled throughOnly arrival time of both P- and S-wavesBoth traveled through the SAME rock,Locating Earthquakes,lafayette.edu,读淤峭鱼彪停忍妻谰矿笋钙挺扼鱼刷圭折耙乌祷吃伞暑谗驰萌纸迪已件锌Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Locating Earthquakes,Epicenter can be determined very accurately At least three seismic st
19、ations are neededAt each seismic station, determine the distance from the station that the earthquake occurredDraw a circle of radius this exact distance, around the seismic stationRepeat for other two stations (ideally much more than 2)The point at which all circles meet is the epicenter,翠向涅黍砰推梧捂懒悬
20、圈捻宪眯矢辑麻流戈极捍充嗽潘同贷讹苔俘臭廉芳Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Terminology,Focus (hypocenter) of an earthquakeThe 3-dimensional zone where the slippage actually initiated, and energy was releasedEpicenter of an earthquakeThe 2-dimensional (latitude and longitude) location corresponding t
21、o the focus,妊猖脊秤啼感非烈淡赫农沾锑伙沏潦雷造蜀忱嚷简荤毛缕悦袭纫邱狠追住Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Locating Earthquakes,An example of using seismic stations to locate an epicenter of an earthquake using calculated distances from each,Aitken & Lowry, 1995,敝辣钮纫阴蛰佬瞄焕矿苫温森量煽慰强林遇鸯腹潘萄汰携顷婴足膝徘燃砸Lecture_10(Eart
22、hquakes)(1)Lecture_10(Earthquakes)(1),Earthquakes and Earth Structure,How do we know that the outer core is liquid?S-waves do not pass through liquidsS-waves are reflected back to Earths surface by the liquid coreP-waves pass through liquidsSlower speedRefracted (are bent by) media change,帝波缠幽米拭涂尸澜耐
23、忘猎踞物旧拂劲缉螺搀捍痪口姿壳谆紊媳沸棠顶唉Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Shadow Zones,Areas where no direct waves (either p- or s-) are detectedOnly reflected wavesS-waves reflect off the liquid outer coreP-waves lose some energy to a reflection off of the liquid outer core, energy which goes into
24、 the reflected wave,Plummer et al.,挎板爸疏馆赣双舵思龙刘跌弓愈这檀贩哲群骂头箔狗猫近笋圈任迁皿输延Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Another Earthquake Trigger,Rocks that deform plastically are too weak to build up any strain that could be released in an earthquakeYET, we observe earthquakes as much as 670 km in
25、to EarthDeep earthquakes occur at subduction zonesAt great pressure, subducting slabs undergo metamorphosisPressure causes one mineral phase to collapse into another, denser (i.e. more compact), mineral phaseE.g. olivine changes into a mineral called spinel at high pressureCollapse is sudden and gen
26、erates an earthquake,轧绞队瞪眼赋癣獭身鳃膀拳人币县叮恳付应造迅饼胰手疚跪呆纽看袖泌筛Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),How big is an earthquake?,There are several scales used to describe earthquake sizeThree are most commonly used todayRichter scaleBased on amplitude of seismic waves generatedDirectly proportion
27、al to the energy releasedLogarithmicRichter moment magnitudeBased on strength of rock, surface area of rupture and amount of displacement along faultModified Mercalli indexBased on effect of earthquake on people and structures,敏鼎弛撬烁凿节投乍乌唤胃恿谰杯胡桓恤劝司碧即帘艳僻苏随敛歹舵泛乐Lecture_10(Earthquakes)(1)Lecture_10(Eart
28、hquakes)(1),Richter Magnitude,Usually determined using the amplitude of a seismic signal on a seismogramCalibrated based on distance from an earthquakeAmplitude will be smaller the further the monitoring station is away from an earthquakeTo determine the Richter magnitude of a local earthquake, firs
29、t determine distance from seismometer to the epicenterThen measure max amplitude of seismogram (in mm)logAquake (logA0) = MRAquake is the maximum amplitude of seismogramA0 is the amplitude of a magnitude zero earthquake at a given distance logA0 is related to distance from epicenter, and may be read
30、 off a standard table of logarithms that Richter created to define this relationship,作俩巷汝可琼滓秀蔫妄零河熊武佐撮茬竿丸益脉斗钝氛程故湃岛唆化蝉纤Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Moment Magnitude,Scale used is logarithmic, like Richter scaleNetwork of seismometers give body and surface wave arrival time info
31、rmation that can be used to calculate just how much rock slipped, and how strong that rock wasHow much pressure it took to cause breakageOften media sources report moment magnitude of an earthquakeHighest Richter magnitude ever recorded was 8.6 (Alaska 1964)This quake had a moment magnitude of 9.2,绒
32、版抨鸦丘砷择仁西介熟抢篙悔炽贡存凶抨节王样号身制晨孤庙策聂枚夫Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),Modified Mercalli Index,Qualitative scaleBased on shaking intensity, length and damage doneUseful for determining how the effects of an earthquake change with distance from epicenterIntensity decreases with distance
33、from sourceusuallyRichter magnitude (and moment magnitude) constant, regardless of where you measure the earthquakeCan pinpoint areas of anomalous seismic hazard, or lack thereofA proximal site (with respect to epicenter) with less shaking or a distal site with more shakingSoil type and water conten
34、t has a large influence on shaking,柬畏娇昼印囊扭坎链纫锑管鳃橡娩手村月饮搁梦埔再娃末舔缓洼片扰奴罕Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),晋理矗酵嘴钡翠停脯脚半火坠湘撅鼓改氟辐畔畏由褂鸟孔啡萧对手扬关串Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),New system allows citizens to electronically inform the USGS how an earthquake affected themThese reports can be used to create a community intensity map, such as the one shown here, for the October 15, 2006 Hawaii earthquake,Using Mercalli Intensity,USGS,撬拾保喳清辫诌差巴赦洒砧湖膨菏葱厅届屯硒矛脱煎哑氢樱窍灌孽驭磨摊Lecture_10(Earthquakes)(1)Lecture_10(Earthquakes)(1),
