The seis­mic catas­tro­phe in ‘San An­dreas’

Sep­a­rat­ing earth­quake fact from fic­tion in 分辦《加州大地震》中的事實與虛構

The China Post - - GUIDE POST -

The San An­dreas Fault awak­ens, un­leash­ing back-to-back jolts that leave a trail of mis­ery from Los An­ge­les to San Fran­cisco. Sky­scrapers crum­ble. Fires erupt. The letters of the Hol­ly­wood sign top­ple. Tsunami waves swamp the Golden Gate Bridge. In the film "San An­dreas," South­ern Cal­i­for­nia is rocked by a pow­er­ful mag­ni­tude- 9.1 quake fol­lowed by an even stronger mag­ni­tude- 9.6 in North­ern Cal­i­for­nia. U.S. Ge­o­log­i­cal Sur­vey seis­mol­o­gist Su­san Hough ac­com­pa­nied The As­so­ci­ated Press to a screen­ing of the film. De­spite the im­plau­si­ble plot, she said the San An­dreas Fault will in­deed break again, and with­out warn­ing. "We are at some point go­ing to face a big earth­quake," she said.

The San An­dreas Fault has long been con­sid­ered one of the most dan­ger­ous earth­quake faults be­cause of its length. At nearly 1,290 kilo­me­ters long, it cuts through Cal­i­for­nia like a scar and is re­spon­si­ble for some of the largest shakers in U.S. history. The San An­dreas Fault is no­to­ri­ous for pro­duc­ing big ones, but a mag­ni­tude-9 or larger is vir­tu­ally im­pos­si­ble be­cause the fault is not long or deep enough, Hough noted. The most pow­er­ful tem­blors in recorded history have struck along off­shore sub­duc­tion zones where one mas­sive tec­tonic plate dives be­neath another. The 1960 mag­ni­tude-9.5 quake off Chile is the cur­rent world record holder. The San An­dreas Fault has re­vealed its awe­some power be­fore. In 1906, a mag­ni­tude-7.8 re­duced parts of San Fran­cisco to fiery rub­ble. Nearly five decades ear­lier, a sim­i­lar-sized quake rat­tled the south­ern end of the fault.

In 2008, the U.S. Ge­o­log­i­cal Sur­vey led a team of 300 ex­perts that wrote a script de­tail­ing what would hap­pen if a mag­ni­tude-7.8 hit the south­ern San An­dreas Fault. They wanted to cre­ate a science-based cri­sis sce­nario that can be used for pre­pared­ness drills. The les­son: It doesn't take a mag­ni­tude-9 or greater to wreak havoc. Re­searchers cal­cu­lated a mag­ni­tude-7.8 would cause 1,800 deaths and 50,000 in­juries. Hun­dreds of old brick build­ings and con­crete struc­tures and a few high-rise steel build­ings would col­lapse. Com­puter mod­els show the San An­dreas Fault is ca­pa­ble of pro­duc­ing a mag­ni­tude-8.3 quake, but any­thing larger is du­bi­ous.

In the film, Lawrence Hayes, a fic­tional seis­mol­o­gist (played by Paul Gia­matti) no­tices spikes in "mag­netic pulses" that light up Cal­i­for­nia like a Christ­mas tree, herald­ing a mon­ster quake.

In re­al­ity, de­spite a cen­tury of re­search, earth­quake pre­dic­tion re­mains elu­sive. Sci­en­tists can't pre­dict when a jolt is com­ing and are gen­er­ally pes­simistic about ever hav­ing that abil­ity. Ev­ery warn­ing sign scru­ti­nized — an­i­mal be­hav­ior, weather pat­terns, elec­tro­mag­netic sig­nals, at­mo­spheric ob­ser­va­tions, lev­els of radon gas in soil or ground­wa­ter — has failed. "We wish it were as sim­ple as the movie por­trays. It isn't. Re­searchers have scoured ev­ery imag­in­able sig­nal try­ing to find re­li­able pre­cur­sors, but noth­ing has panned out," Hough said.

聖安德魯斯斷層甦醒,一波波地震從洛杉磯到舊金山接連發生,舉目所及滿目瘡痍。摩天大樓倒塌、火災不斷發生、好萊塢的標誌遭到摧毀,就連金門大橋也被海嘯吞沒。在電影《加州大地震》中,九點一級的強震先是侵襲南加州,隨後又有一個規模更強大的九點六級地震在北加州發生。美國地質調查局地震學家蘇珊霍夫陪同美聯社出席這部電影的首映會。儘管電影情節令人難以置信,她表示聖安德魯斯斷層的確會再次毫無預警地爆發地震。她說:「 我們未來的某個時候將會遭遇一個強烈的地震。」

聖安德魯斯斷層因其長度,一直被認為是最危險的地震斷層之一。長達近一千兩百九十公里的聖安德魯斯斷層就像一道穿越加州的傷疤,美國歷史上幾次規模最大的地震都源於這條斷層。霍夫指出,雖然聖安德魯斯斷層以引起大地震而惡名昭彰,但規模九級或更大的地震幾乎是不可能發生的,因為這條斷層不夠長、也不夠深。史上最強烈的地震都在沿海隱沒帶出現,剛好是一個巨大板塊潛至另一板塊下方的地帶。一九六○年在智利沿海發生的規模九點五級地震是目前世界上最強烈的地震,聖安德魯斯斷層過去就已展現過其可怕的威力。一九○六年規模七點八級的地震令舊金山成陷入一片火海及殘骸之中。而時間再往前推約五十年,一個類似規模的地震也襲擊了這條斷層的南端。

○○八年,美國地質調查局帶領一個由三百名專家組成的團隊撰寫一套模擬劇情,詳細說明如果一個規模七點八級的地震襲擊聖安德魯斯斷層南端,將會造成何等的後果。他們想創造出一個以科學為基礎的災難場景,以用於地震防範的演練。而結論是,就算不是規模九級或更大的地震,也可能造成這個地區的嚴重災情。研究人員計算出,一個規模七點八級的地震會造成一千八百人至五萬人死亡或受傷。數以百計的老式磚樓和混凝土建築,以及一些高層鋼架建築將會崩塌。電腦模型顯示,聖安德魯斯斷層可能會產生一個規模八點三級的地震,更大地震發生的可能性則較低。

在電影中,一個虛構的地震學家勞倫斯海耶斯(保羅賈麥提飾)指出,「磁脈衝」會使加州像聖誕樹一樣發光,並預示著巨大地震的到來。

在現實中,儘管經過一個世紀的研究,地震預警仍然遙遙無期。科學家無法預測地震什麼時候來臨,且對於發展出這種能力的可能性感到相當悲觀。每一種警示訊息都被檢視,包括動物行為、天氣模式、電磁信號、大氣觀測、以及土壤或地下水的氡氣含量,但都徒勞無功。霍夫說:「我們希望事實能如

同電影描繪的那樣簡單,但卻並非如此。研究人員試過每一個

他們想像過的方式,試圖尋找可靠的地震前兆,但一切都沒有

結果。」

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