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Transcript
Base your answers to questions 24 through 28 on the following map, The map shows the time of arrival of seism-ic sea waves (tsunamis) from locations throughout the Pacific Ocean to the Hawaiian lslands. For example, an earthquake at any loGtion on the line labeled '6 h' could prcduce a tsunami that would arrive in Honolulu 5 hour later. ‐ ヽ Reporting Stations . a 0 5∞ 1000 1 Tide stations Seismograph stations 2000 1 : Distance (miles) From which location would a tsunami arrive at Honolulu in the shortest time? 1 2 Kodiak (3)Tahiti La Jo‖ a (41 Wake iS:and (3)Honolu!u 27. The most likely reason for collecting this Pacific Ocean data is that Honolulu is (l) the site of frequent maior eruptions (2) an equal distance from manY seismic stations 26. Approximately how fast do seismic sea waves travel from Midway to Honolulu, Hawaii? (3)1500to 2000 mph (1)31to 51 mph 14)3000 to 5000 mph (2)300to 500 mph AM● del (3) surrounded by earthquake-prone zones (4) the site of a major tide station 28. O Tahti h = hours : Which reporting station is NOT located on the Pacific plate? (1)HOng Kong (2)Midway ぃ 。 Locations in this region where major earthquakes occur are most closely associated with areas of (1) volcanic eruptions (2) P-wave absorption (3) magnetic field reversal (4) mid-continental folding Start Here of■ artht h“ erl● 『 :ヨ :T∬1:田 語 影議RI油出塁讐:馴鼠嘗僣雷轟議期よ」 the study of earthquake waves. Topic l2: Earth3 Dynamic Crust and lnterior 255 Methods of Studying Earth,s lnterior The deepest mines are little more than 3.5 kilometers deep, and the deepest drill hole (in Russia) is approximately 12 kilometers deep. ffri, f Z kilometers represents less than 0.2 pircent of the distance to the center of Earth. properties of Earth,s interior through the study T"ibT (earthquake) the of seismic S"r.^ost.of waves. This is much the same as stud/ing truman interiors with methods such as X-rays, ultrasounds, and CAT scais, By comparing thousands of seismograms from hundreds of locations, scientists have determined the times the different types of seismic waves arrive and when they don't arrive at numerous lociiions around Earth. By comparing these records with tests done using explosives in the oil industry and tests with nuclear bombs, scienti-sts discovered that seismic *"y"r fj".j1Tflect, change velocity, and become absorbed by various parts of Earth's interior. Figures 12-10 and 12-11 show the most corunon model of Earth's interior that has resulted from these seismic wave studies. Zones of Earth Our analysis of seismic waves indicates that Earth is composed of a number of zones, as shown in Figures 12-10 and 12-11, The crust is the outermost part of Earth below the atmosphere or hydrosphere. Though mostly solid rock, the crust includes the ioil and eroded and weatheid rock deposits. Below the crust is the mostly solid part called the mantle, Earth's thickest zone that contains approximatellg0 percent of Earth,s The mantle is separated from the crust by a ttLln interface caled 1olurn9. the Moho. Below the Moho, the rocks become denser. The whole crust and F" "9V "f-g"11ost portion of the mantle (called the rigid mantle) are together called the lithosphere. (See Figure 12-11.) The lithosphere is Earthquake focus O. 60° lo2° 120。 143° Distance in degrees 102° ……>Refracted ――) Rttected waves waves 寵 変 訥 ざ F1911ぃ ●■2・ ■0.Arr:v● :ti_and Paths Of seismic waves moving thrOugh Earthヽ :nterion Ana:ysis of the■ mes seismic waves ar"ve has resulted in interpetat10ns of ref:ecuons and refractions ofthtt waves in Eartht inte"or This analysis has resu:ted in the dら ぃ ● standad “ “ 256 ■^_^_^_^=‐ __‐ ●│ model of the zone! ot Earth! lnterior ihown herE“ ^.I_1^`● fopt tz: Eanhb Dynamrc C.usr and tnteflor divided into sections called "plates," which you will study in the next section. 襦 Below the lithosphere is another portion of the upper rnantle called the asthenosphere. This zone was discovered because it was found that seismic waves decreased in velocity from approximately 100 to 700 kilometers below Earth's surface. The asthenosphere is believed to be a plasticJike portion of the upper mantle that is at least Partly 2 center 0 8 6 4 2 0 4 3 2 1 /だ じ ︲ ︲ t ぶ / n a れ ヅ 珈 ′ m0 0 0 0 0 5 0 。 0 4 0 0 0 3 。 0 0 2 differences in composition and density. 5一 C 00こ こ0一 ﹂ ︵ ︺︶o﹂ o The two crusts are also distinguished by 127131 \Earthヽ 。 0 。 6 coastal regions. Andes Trench 0ヽ3一〇0﹂α Earth's Crust Earth's crust, or upper lithosphere, is divided into two major divisions. The continental crust makes up the continents and larger islands, and the oceanic crust makes up most of the crust beneath the oceans. The continental crust is usually much thicker than the oceanic crust. The contential crust is thickest where highest-in mountain regions-and usually thinnest beneath h° 99‐ 122 ● ob ‘0いoE に いo ∽cp 〓 E ︶ Figure 12-10 shows the outermost dimension-by area---of the shadow zone of the outer core that, due to refraction, does not receive any refracted seismic waves. The bottom of the outer core is indicated by the waves reflected off the outside edge of the inner core. Figure 12-10 also provides evidence that the outer core is liquid: Because no 9waves pass through the zone, it can't be a solid, and because the zone has too much pressure, it cannot be a gas. The 9waves are absorbed as they enter the outer core. The liquid nature of the outer core is also indicated by the major drop in P-wave velocity, as shown in Figure 12-11. Beneath the outer core is the inner core extending down to Earth's center. Due to the great pressures and the increase in P-wave velocity at the inner core (as shown in Figure l2-11), the inner core is believed to be a solid. 3.0 oceanic 4 Beneath the mantle Earth's core is divided into two parts-the inner core and the outel core. III ↑M° い 0一 OEO〓〓︶ ﹂ ︵COυoい ヽ O む一 υp9 ・ molten. Much of the magma and lava of the crust and lithosphere is thought to originate in this zone. Note on the temPerature graph in Figure 12-11 that the melting Point and temperature curve intersect, indicating this partial melting. The asthenosphere allows the plates of the lithosphere to move around Earth's surface and to move up and down. Below the asthenosphere is the maiority of the mantle, called the stiffer mantle. :潟 υ 7 continental 1000 0 0 10002000 3000400050006000 Depth(km) FIgurG l2-ll. Properties and zonet of Earth's interior: Analysis of the seismic wave! and other studies have resulted in the inlejen(e about Earth! interior illurtrated here. Note that most ot Earthb interior i5 solid except for the outer <ore and portions of the asthenosphere, both ot which are liquid' (See algo the lnferred Properties of Earth3 lnterior in the Earth scr'ence Befetence lablet., Topic 12: Earth's Dynamic Crustand lnterior 257 The continental crust is made largely of granitic ^ (p rocks-rocks with a mineral or chemical composition similar to granite. The oceanic crust is composed mostly of basaltic rocks-rocks similar in mineral or chemical composition to basalt. The granite is less dense than the basalt; thus, the granitic continental crust is less dense than the basaltic oceanic crust. See the average value of the density of the continental crust and oceanic crust on the Ir:rferred Properties of Earth,s Interior in the Earth Science Reference Tables. Composition of Earth's lnterior Many scientists think Earth,s inner and outer core are composed largely of iron and nickel. There is much evidence to support this hypothesis, including the iron and nickel composition of many meteorites and Earth's magnetism-iron and nickel are two of a few magnetic elements. In addition, a combination of iron and nickel at the temperafures and pressures believed to be in Earth,s core can account for the observed properties of the seismic waves that pass tfuough the core. The high-density iron-nicke-l composition of the core and the low-density composition of the crust indicate that the mantle must have a composition different from the crust and the core and an interrnediate density. : (!) 29. Earth's crust is composed mostly of rocks and minerals, as illustrated on the various charts in the Edrth Science Reference Tables depicting minerals, sedimentary rocks, metamorphic rocks, and ign"ors .o"-ks. Geierally, the crust is composed of low-density rocks with a mixture of granitic and basaltic cornpositions. ln developing a model of Earth,s deep interior, most of the evidence was derived from (1) deep wells (2) mining operations (3) observation of other planets (4) seismic data 30. Through which zones (P-waves) travel? of Earth do primary waves (1) only the crust and mantle (2) only the mantle and outer core (3) onlythe outer and inner core (4) the crust, mantle, outer core, and inner core 31. According to the Earth Science Reference TableT in which group are the zones of Earth,s interior correctly arranged in order of increasing averい0 ●“ age density? 258 crust, mantle, outer core, inner core crust, mantle, inner core, outer core inner core, outer core, mantle, crust outer core. inner core, mantle, crust fopic t U: Earth's Dynamic Crust and tnterior 32. What evidence has been obtained concerning the existence of the Moho and Earth,s mantla? (1) satellite images (2) well drillings (3) exposures in deep canyons like the Grand Canyon (4) refraction of earthquake waves 33. What is the relationship among density, temperature, and pressure inside Earth? (1) As depth increases, density, temperature, and pressure decrease. (2) As depth increases, density and temperature increase, but pressure decreases. (3) As depth increases, density increases, but temperature and pressure decrease. (4) As depth increases, density, temperature, and pressure increase. !14. ln which parts of Earth's interior would melted or partially melted material be found? (1) stiffer mantle and inner core (2) stiffer mantle and outer core (3) crust and inner core (4) asthenosphere and outer core How does thickness and density of the continental crust compare to that of the oceanic crust? (l) The continental crust is thicker and less dense than the oceanic crust. (2) The continental crust is thicker and denser than the oceanic crust. (3) The continental crust is thinner and less dense than the oceanic crust. (4) The continental crust is thinner and denser than the oceanic crust. An earthquake occurs in city A. Recordings on a seismograph in city B show only the presence of P-waves. City A and B are on opposite sides of Earth-180' apart. what does this information allow you to infer about the structure of Earth's interior? How does the composition oJ the oceanic crust compare with the composition of the continen- tal crust? (1) The oceanic crust is mainly limestone, while the continental crust i5 mainly sandstone. (2) The oceanic crust is mainly limestone, while the continental crust is mainly granitic. (3) The oceanic crust is mainly basaltic, while the continental crust is mainly sandstone. (4) The oceanic crust is mainly basaltic, while the continental crust is mainly granitic. 39. The overall density of Earth is approximately 5.5 9/cm3. The average density of Earth's crust is between 2.5 gtcm3 and 3.0 g/cmr. What does this suggest about the density of Earth's core? 40. The composition of some meteorites supports the inference that Earth's core is corlposed of (l) Stop Here 41. The temperature of rock located 1000 kilometers below Earth's surface is approximately 1 2 00 つυ 助 crust generally decreases increases remains the same aluminum and calcium (2) iron and nickel (3) silicon and oxYgen (4) magnesium and potassium 37. As one travels from an ocean shore to the interior of a continent, the thickness of Earth's 1000° C 2600° C 3300° C 4300° C Plate lbctonics People have always wondered about the origin of continents, mountain ranles, volcanoes, earthquakes, and the multitudes of other features and err"its. In the pust, many legends, religious beliefs, and scientific theories have hied to explain Earth's features and events. Some of the older scientific theories include cooling and contraction of Earth, expansion of Earth, and continental drift. None of these earlier theories seems satisfactory for most of the scientific community today. Since the 1960s many new discoveries from the studies of ocean drilling, Earth's magnetism, satellite observations, and detailed analysis of rocks and fossils hav-e led to *re plate tectonic theory. This theory has done for the earth sciences what evolution and genetics have done for the biological sciences' It has provided a unifying model to explain most, if not all, rnajor features and events of Earth's lithosphere. The Plate Tectonic TheorY The basic concept of the plate tectonic theory is that Earth's lithosphere is broken up into sections or pieces called plate*also called lithospheric plates and iectonic plates-and their movement and interaction produce major changes in Earth's surface. In this book the term "plates" will mosdy be used. These plates move about Earth's surface at a rate of a few centimeters per year (ipproximately the rate of fingemail growth)' These plates can also move up and down-usually at rates of only millimeters per y€ar--due to uplifting and sinking. The plates can move around and up and down because"they are floitlng on the asthenosphere--a plasticJike layer of the mantle' Topic 12: Earths Dynamic crusl and lnterior 259 !e{er to fjqle t2-12 and the lbctonic plates map in the Earth Scimce (D familiar with the namis and locations of the various plates. You will observe that the plates usually don,t follow continent or ocean boundaries. Note tnaitfre North Rmerican plate includes parts of Asia and North America; the pacific, Arctic, and the Atlantic Oceans; and Greenland and part of lceland. Westemmost Refermce Tablw to become Califomia and Mexico are part of the pacific plate. Most plates have continmta_l and oceanic cnrst at their tops. Almail number of plates are oceanic-that is, they have only oceaniC cmst at their tops, like the Nazca and Philippine plates. At least three times, if not more, most of the large landmasses (continents and larger islands) have come together, formin! supercontinents. Figure 12-12 shows how the supercontinent Rdin; formed approximately 800 million years ago and how the continmts have split and formed since' then. Note that diagrams G and H indicate the proiected positions of landmasses in the future, based on the rates ana dfuections the plates are moving in now The Three flpes of plate Boundaries As tfie plates move, they interact in three ways-they can separate, collide, and slide by each other. Most of the major evints involving Earth,s such as mountain building, earthquakes, and volcanic eruptions_occur at Uo.un$a1a yhere the plates interact. Each of the three-types of plate $e boundaries has its own set of unique events and features, whicfr are crusj illustrated in Figure 12-13. Diuergent Platc Eoundaries Wherc two plates sqrarate, or diverge, the boundary is catled a divergent ptate Uounaary. tfr"s" to"utio.E tt pt"t"" ^dt move apart and magma rises from below to fill in the separation, resulting " in igneous intrusions and extrusions, such as lava flows^urrd volca.roes. (See Figure 12-138.) This divergmce is sometimes called sea-floor spreading. " Thig magm? and resulting lava form igneous rock that creates new crust and lithosphere, which are then sptit and divided in two by the divefueice. The magma that forms in these regions is the result of divJrgence thai lowers the- confiningpressure and-melts rocks of the lower li-thosphere and asthenosphere. The divetgence also results in many earthquakes, most of which are shallow in depth. If the divergmce is wiihin thJcontinental crust, the result is a continental rift valley of mountains created by faulting and much volcanic activity. (See Figure iZ-taa.; Whm the divergmce is within oceanic crust,.the faulting and volcanic activity result in a mid-ocean ridge, a mountain range atihe bottom of theocean that is composed moslly of volcanoes ani lava flows. The mid-ocean-ridges often have a central depression, or rift valley, as shown in Figure 12-138. Convergent Plate Boundaries When two plates collide, or converge, the result is a convergent plate bounaary, Much of the dramatic events and feafures of Earth's crust are deated it these convergent boundaries. There are three varieties of convergent plate boundaries: o both plates with oceanic crust on top 260 Topic 12: Earthi Dynamic Crust and tnterior