万物简史英文版_比尔·布莱森-第40章

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！


at　an　angle；　as　if　they　had　encountered　some　kind　ofbarrier。　from　this　he　deduced　that　the　earth　has　a　core。　three　years　later　a　croatianseismologist　named　andrija　mohorovi？i鈥瞔　was　studying　graphs　from　an　earthquake　in　zagrebwhen　he　noticed　a　similar　odd　deflection；　but　at　a　shallower　level。　he　had　discovered　theboundary　between　the　crust　and　the　layer　immediately　below；　the　mantle；　this　zone　has　beenknown　ever　since　as　the　mohorovi？i鈥瞔　discontinuity；　or　moho　for　short。

we　were　beginning　to　get　a　vague　idea　of　the　earth鈥檚　layered　interior鈥攖hough　it　really　wasonly　vague。　not　until　1936　did　a　danish　scientist　named　inge　lehmann；　studyingseismographs　of　earthquakes　in　new　zealand；　discover　that　there　were　two　cores鈥攁n　innerone　that　we　now　believe　to　be　solid　and　an　outer　one　（the　one　that　oldham　had　detected）　thatis　thought　to　be　liquid　and　the　seat　of　magnetism。

at　just　about　the　time　that　lehmann　was　refining　our　basic　understanding　of　the　earth鈥檚interior　by　studying　the　seismic　waves　of　earthquakes；　two　geologists　at　caltech　in　californiawere　devising　a　way　to　make　parisons　between　one　earthquake　and　the　next。　they　werecharles　richter　and　beno　gutenberg；　though　for　reasons　that　have　nothing　to　do　with　fairnessthe　scale　became　known　almost　at　once　as　richter鈥檚　alone。　（it　has　nothing　to　do　with　richtereither。　a　modest　fellow；　he　never　referred　to　the　scale　by　his　own　name；　but　always　called　it鈥渢he　magnitude　scale。鈥潱﹖he　richter　scale　has　always　been　widely　misunderstood　by　nonscientists；　though　perhapsa　little　less　so　now　than　in　its　early　days　when　visitors　to　richter鈥檚　office　often　asked　to　seehis　celebrated　scale；　thinking　it　was　some　kind　of　machine。　the　scale　is　of　course　more　anidea　than　an　object；　an　arbitrary　measure　of　the　earth鈥檚　tremblings　based　on　surfacemeasurements。　it　rises　exponentially；　so　that　a　7。3　quake　is　fifty　times　more　powerful　than　a6。3　earthquake　and　2；500　times　more　powerful　than　a　5。3　earthquake。

at　least　theoretically；　there　is　no　upper　limit　for　an　earthquake鈥攏or；　e　to　that；　a　lowerlimit。　the　scale　is　a　simple　measure　of　force；　but　says　nothing　about　damage。　a　magnitude　7quake　happening　deep　in　the　mantle鈥攕ay；　four　hundred　miles　down鈥攎ight　cause　no　surfacedamage　at　all；　while　a　significantly　smaller　one　happening　just　four　miles　under　the　surfacecould　wreak　widespread　devastation。　much；　too；　depends　on　the　nature　of　the　subsoil；　thequake鈥檚　duration；　the　frequency　and　severity　of　aftershocks；　and　the　physical　setting　of　theaffected　area。　all　this　means　that　the　most　fearsome　quakes　are　not　necessarily　the　mostforceful；　though　force　obviously　counts　for　a　lot。

the　largest　earthquake　since　the　scale鈥檚　invention　was　（depending　on　which　source　youcredit）　either　one　centered　on　prince　william　sound　in　alaska　in　march　1964；　whichmeasured　9。2　on　the　richter　scale；　or　one　in　the　pacific　ocean　off　the　coast　of　chile　in　1960；which　was　initially　logged　at　8。6　magnitude　but　later　revised　upward　by　some　authorities（including　the　united　states　geological　survey）　to　a　truly　grand…scale　9。5。　as　you　will　gatherfrom　this；　measuring　earthquakes　is　not　always　an　exact　science；　particularly　wheninterpreting　readings　from　remote　locations。　at　all　events；　both　quakes　were　whopping。　the1960　quake　not　only　caused　widespread　damage　across　coastal　south　america；　but　also　set　offa　giant　tsunami　that　rolled　six　thousand　miles　across　the　pacific　and　slapped　away　much　ofdowntown　hilo；　hawaii；　destroying　five　hundred　buildings　and　killing　sixty　people。　similarwave　surges　claimed　yet　more　victims　as　far　away　as　japan　and　the　philippines。

for　pure；　focused；　devastation；　however；　probably　the　most　intense　earthquake　in　recordedhistory　was　one　that　struck鈥攁nd　essentially　shook　to　pieces鈥攍isbon；　portugal；　on　all　saintsday　（november　1）；　1755。　just　before　ten　in　the　morning；　the　city　was　hit　by　a　suddensideways　lurch　now　estimated　at　magnitude　9。0　and　shaken　ferociously　for　seven　full　minutes。

the　convulsive　force　was　so　great　that　the　water　rushed　out　of　the　city鈥檚　harbor　and　returnedin　a　wave　fifty　feet　high；　adding　to　the　destruction。　when　at　last　the　motion　ceased；　survivorsenjoyed　just　three　minutes　of　calm　before　a　second　shock　came；　only　slightly　less　severe　thanthe　first。　a　third　and　final　shock　followed　two　hours　later。　at　the　end　of　it　all；　sixty　thousandpeople　were　dead　and　virtually　every　building　for　miles　reduced　to　rubble。　the　san　franciscoearthquake　of　1906；　for　parison；　measured　an　estimated　7。8　on　the　richter　scale　andlasted　less　than　thirty　seconds。

earthquakes　are　fairly　mon。　every　day　on　average　somewhere　in　the　world　there　aretwo　of　magnitude　2。0　or　greater鈥攖hat鈥檚　enough　to　give　anyone　nearby　a　pretty　good　jolt。

although　they　tend　to　cluster　in　certain　places鈥攏otably　around　the　rim　of　the　pacific鈥攖heycan　occur　almost　anywhere。　in　the　united　states；　only　florida；　eastern　texas；　and　the　uppermidwest　seem鈥攕o　far鈥攖o　be　almost　entirely　immune。　new　england　has　had　two　quakes　ofmagnitude　6。0　or　greater　in　the　last　two　hundred　years。　in　april　2002；　the　region　experienceda　5。1　magnitude　shaking　in　a　quake　near　lake　champlain　on　the　new　york鈥搗ermont　border；causing　extensive　local　damage　and　（i　can　attest）　knocking　pictures　from　walls　and　childrenfrom　beds　as　far　away　as　new　hampshire。

the　most　mon　types　of　earthquakes　are　those　where　two　plates　meet；　as　in　californiaalong　the　san　andreas　fault。　as　the　plates　push　against　each　other；　pressures　build　up　untilone　or　the　other　gives　way。　in　general；　the　longer　the　interval　between　quakes；　the　greater　thepent…up　pressure　and　thus　the　greater　the　scope　for　a　really　big　jolt。　this　is　a　particular　worryfor　tokyo；　which　bill　mcguire；　a　hazards　specialist　at　university　college　london；　describesas　鈥渢he　city　waiting　to　die鈥潯。╪ot　a　motto　you　will　find　on　many　tourism　leaflets）。　tokyo　standson　the　boundary　of　three　tectonic　plates　in　a　country　already　well　known　for　its　seismicinstability。　in　1995；　as　you　will　remember；　the　city　of　kobe；　three　hundred　miles　to　the　west；was　struck　by　a　magnitude　7。2　quake；　which　killed　6；394　people。　the　damage　was　estimatedat　99　billion。　but　that　was　as　nothing鈥攚ell；　as　paratively　little鈥攑ared　with　whatmay　await　tokyo。

tokyo　has　already　suffered　one　of　the　most　devastating　earthquakes　in　modern　times。　onseptember　1；　1923；　just　before　noon；　the　city　was　hit　by　what　is　known　as　the　great　kantoquake鈥攁n　event　more　than　ten　times　more　powerful　than　kobe鈥檚　earthquake。　two　hundredthousand　people　were　killed。　since　that　time；　tokyo　has　been　eerily　quiet；　so　the　strainbeneath　the　surface　has　been　building　for　eighty　years。　eventually　it　is　bound　to　snap。　in　1923；tokyo　had　a　population　of　about　three　million。　today　it　is　approaching　thirty　million。　nobodycares　to　guess　how　many　people　might　die；　but　the　potential　economic　cost　has　been　put　ashigh　as　7　trillion。

even　more　unnerving；　because　they　are　less　well　understood　and　capable　of　occurringanywhere　at　any　time；　are　the　rarer　type　of　shakings　known　as　intraplate　quakes。　thesehappen　away　from　plate　boundaries；　which　makes　them　wholly　unpredictable。　and　becausethey　e　from　a　much　greater　depth；　they　tend　to　propagate　over　much　wider　areas。　themost　notorious　such　quakes　ever　to　hit　the　united　states　were　a　series　of　three　in　newmadrid；　missouri；　in　the　winter　of　1811鈥�12。　the　adventure　started　just　after　midnight　ondecember　16　when　people　were　awakened　first　by　the　noise　of　panicking　farm　animals　（therestiveness　of　animals　before　quakes　is　not　an　old　wives鈥櫋�tale；　but　is　in　fact　well　established；though　not　at　all　understood）　and　then　by　an　almighty　rupturing　noise　from　deep　within　theearth。　emerging　from　their　houses；　locals　found　the　land　rolling　in　waves　up　to　three　feet　highand　opening　up　in　fissures　several　feet　deep。　a　strong　smell　of　sulfur　filled　the　air。　theshaking　lasted　for　four　minutes　with　the　usual　devastating　effects　to　property。　among　thewitnesses　was　the　artist　john　james　audubon；　who　happened　to　be　in　the　area。　the　quakeradiated　outward　with　such　force　that　it　knocked　down　chimneys　in　cincinnati　four　hundredmiles　away　and；　according　to　at　least　one　account；　鈥渨recked　boats　in　east　coast　harbors　and　。

。　。　even　collapsed　scaffolding　erected　around　the　capitol　building　in　washington；　d。c。鈥潯�onjanuary　23　and　february　4　further　quakes　of　similar　magnitude　followed。　new　madrid　hasbeen　silent　ever　since鈥攂ut　not　surprisingly；　since　such　episodes　have　never　been　known　tohappen　in　the　same　place　twice。　as　far　as　we　know；　they　are　as　random　as　lightning。　the　nextone　could　be　under　chicago　or　paris　or　kinshasa。　no　one　can　even　begin　to　guess。　and　whatcauses　these　massive　intraplate　rupturings？　something　deep　within　the　earth。　more　than　thatwe　don鈥檛　know。

by　the　1960s　scientists　had　grown　sufficiently　frustrated　by　how　little　they　understood　ofthe　earth鈥檚　interior　that　they　decided　to　try　to　do　something　about　it。　specifically；　they　got　theidea　to　drill　through　the　ocean　floor　（the　continental　crust　was　too　thick）　to　the　mohodiscontinuity　and　to　extract　a　piece　of　the　earth鈥檚　mantle　for　examination　at　leisure。　thethinking　was　that　if　they　could　understand　the　nature　of　the　rocks　inside　the　earth；　they　mightbegin　to　understand　how　they　interacted；　and　thus　possibly　be　able　to　predict　earthquakes　andother　unwele　events。

the　project　became　known；　all　but　inevitably；　as　the　mohole　and　it　was　pretty　welldisastrous。　the　hope　was　to　lower　a　drill　through　14；000　feet　of　pacific　ocean　water　off　thecoast　of　mexico　and　drill　some　17；000　feet　through　relatively　thin　crustal　rock。　drilling　froma　ship　in　open　waters　is；　in　the　words　of　one　oceanographer；　鈥渓ike　trying　to　drill　a　hole　in　thesidewalks　of　new　york　from　atop　the　empire　state　building　using　a　strand　of　spaghetti。鈥�

every　attempt　ended　in　failure。　the　deepest　they　penetrated　was　only　about　600　feet。　themohole　became　known　as　the　no　hole。　in　1966；　exasperated　with　ever…rising　costs　and　noresults；　congress　killed　the　project。

four　years　later；　soviet　scientists　decided　to　try　their　luck　on　dry　land。　they　chose　a　spot　onrussia鈥檚　kola　peninsula；　near　the　finnish　border；　and　set　to　work　with　the　hope　of　drilling　toa　depth　of　fifteen　kilometers。　the　work　proved　harder　than　expected；　but　the　soviets　weremendably　persistent。　when　at　last　they　gave　up；　nineteen　years　later；　they　had　drilled　to　adepth　of　12；262　meters；　or　about　7。6　miles。　bearing　in　mind　that　the　crust　of　the　earthrepresents　only　about　0。3　percent　of　the　planet鈥檚　volume　and　that　the　kola　hole　had　not　cuteven　one…third　of　the　way　through　the　crust；　we　can　hardly　claim　to　have　conquered　theinterior。

interestingly；　even　though　the　hole　was　modest；　nearly　everything　about　it　was　surprising。

seismic　wave　studies　had　led　the　scientists　to　predict；　and　pretty　confidently；　that　they　wouldencounter　sedimentary　rock　to　a　depth　of　4；700　meters；　followed　by　granite　for　the　next　2；300meters　and　basalt　from　there　on　down。　in　the　event；　the　sedimentary　layer　was　50　percentdeeper　than　expected　and　the　basaltic　layer　was　never　found　at　all。　moreover；　the　world　downthere　was　far　warmer　than　anyone　had　expected；　with　a　temperature　at　10；000　meters　of　180degrees　centigrade；　nearly　twice　the　forecasted　level。　most　s