Study: 99 Percent Probability of Los Angeles-Area Quake
By THE ASSOCIATED PRESS

LOS ANGELES — There is a 99.9 percent chance of a magnitude-5 or greater earthquake striking within three years in the greater Los Angeles area, where a similar sized temblor caused more than $12 million in damage last year, according to a study by NASA and university researchers.

The study released Tuesday was based on Global Positioning System and airborne radar measurements of how the Earth's crust was deformed by the magnitude-5.1 quake on March 28, 2014, in La Habra, about 20 miles southeast of downtown Los Angeles. The damage included broken water mains and cracked pavement.

By comparison, in 1994 the magnitude-6.7 Northridge earthquake left $25 billion in damage, caused dozens of deaths and injured 9,000 people.

The study looked at a 62-mile radius around the La Habra epicenter. Researchers observed shallow movements of the ground, took into account a deficit in the number of earthquakes expected there and calculated how much strain may remain in deeper faults that are still locked.

While the magnitude-5 quake was found to be extremely likely by April 1, 2018, one of magnitude-6 or higher was pegged at just 35 percent and the largest potential quake was estimated at 6.3.

Study leader Andrea Donnellan, a geophysicist at NASA's Jet Propulsion Laboratory, said the research is not a prediction. "It's a statistical probability that we computed," she said in an interview.

The U.S. Geological Survey took issue with the study, asserting that it was unclear how the study derived its numbers and that the accepted probability is 85 percent.

Responding to the criticism, Donnellan said the study's references to other scientific papers would allow other researchers to reconstruct the process.

According to the most recent Uniform California Earthquake Rupture Forecast, which was published in March and is the basis for the agency's National Seismic Hazard Maps, the Southern California region has a 100 percent chance of one or more magnitude-5 or larger quakes and a 93 percent chance of a 6.7 jolt during the next 30 years.

Thousands of older wood and concrete apartment buildings vulnerable to collapse in a major earthquake would get costly upgrades under sweeping retrofitting rules passed this month by the Los Angeles City Council.

Also participating in the NASA-led study were researchers from the University of California, Irvine; Indiana University, Bloomington; UC Davis; and the University of Nevada, Reno.

NASA：洛杉磯3年內99.9%有強震

美國太空總署（NASA）與戴維斯加大等大學在20日聯名發表的一項研究報告中指出，大洛杉磯地區未來三年內發生芮氏規模五或以上強震的機率高達99.9%。

主持這項研究的NASA噴射推進實驗室地球物理學家安德蕾．唐尼倫說，這項研究不是預測，而是「我們經過計算得出的統計或然率」。

去年3月28日，洛杉磯市區西南方的拉哈布拉發生芮氏規模5.1的地震，造成逾1200萬美元的損害。報告參考該次地震發生後，全球定位系統與空中雷達測量災區的地殼變形結果。1994年的洛杉磯北脊芮氏規模6.7強震造成數十人死亡、約9000人受傷，損失高達250億美元。

研究人員檢視震央拉哈布拉周圍半徑100公里內的地區，結果發現地面出現淺層移動。他們並將地區實際地震次數不及原預期的因素納入考量，同時估計可能還有多少能量蓄留在較深層的斷層。

研究人員認為，2018年4月1日之前，大洛杉磯地區發生芮氏規模五或以上地震的機率高達99.9%，發生芮氏規模六或以上地震的機率只有35%，可能發生的最大地震規模則是6.3。

美國地質測量所表示，研究人員並沒有說明如何取得這項報告的數據，而各界公認大洛杉磯地區，在未來發生芮氏規模五或以上地震的機率則是85%。

根據今年3月公布的最新「加州統一地震斷裂預測」，未來30年，南加州地區發生至少一次芮氏規模五或以上地震的機率是百分之百，出現芮氏規模6.7強震的機率則是93%。

原文參照：
http://www.nytimes.com/aponline/2015/10/21/us/ap-us-los-angeles-earthquake-study.html

2015-10-22．聯合晚報．A6．國際焦點．編譯陳世欽