一個由法國與土耳其地震學者組成的研究團隊，最近從觀測資料中發現一種罕見的「超級剪力地震」（supershear earthquake）。這種前所未知的地震爆發時，主斷層會以極高速產生破裂，而且會在距離主斷層較遠的地區引發餘震，破壞力可能相當巨大。
圖1. A quake reading on a seismograph. A French-Turkish team of seismologists on Thursday said they had found evidence about the impacts of a rare but extremely violent earthquake called a supershear.
這項研究由法國「國家科學研究中心」（CNRS）的 Michel Bouchon 博士與土耳其海峽大學「坎地利觀測站與地震研究所」的 Hayrullah Karabulut 博士合作，論文刊於最新一期的美國《科學》周刊。兩位學者指出，超級剪力地震發生時，能量脈衝的行進速度可高達每小時 2 萬 1600 公里，遠高於在岩體內部傳遞的剪力波（S 波），其效應有如戰機以超音速飛掠之後出現的音爆。
圖2. 地震波的種類 － 體波（Body Waves）與表面波（Surface Waves）－圖片來源：http://en.wikipedia.org/wiki/Seismic_wave
這類地震 1999 年在土耳其（Izmit, Turkey）西北部發生過兩次，2001 年在中國西藏、2002 年在美國阿拉斯加州各一次。其中 2001 年 11 月 14 日，發生在青藏高原中北部昆侖山口西的芮氏規模 7.9 地震，地表破裂帶達 425 公里，至今仍是世界紀錄，破裂長度與規模的比例也遠遠超過統計值。不過上個月 12 日的中國汶川大地震仍屬於傳統類型，並非超級剪力地震。
圖3. November 14, 2001 - 發生在西藏芮氏規模 7.9 的地震，在地表上留下的痕跡（圖片來源：http://www.seismo-watch.com/EQS/AB/2001/011114.China.M7.9/011114.China.P1.html）
圖4. November 14, 2001 - 西藏－崑崙山大地震斷層衛星圖（圖片來源：http://www.ipgp.jussieu.fr/~lacassin/Kunlun/kunlun.html）
超級剪力地震並不常見，只會發生在直線排列的特定型態斷層上，讓震波能夠避開障礙、高速前進，並以輻射方式影響遠離主斷層的次級地質構造，引發難以預測的餘震。Bouchon 與 Karabulut 希望進一步研究容易發生超級剪力地震的地區，預先判定可能發生餘震的地區，這類研究對於餘震預警和救災都有幫助。
原始報導：
，更新日期 2008/06/07 04:33 閻紀宇綜合報導原文：
New Study Sheds Light On Mysterious 'Supershear' Quakes
A French-Turkish team of seismologists on Thursday said they had found evidence about the impacts of a rare but extremely violent earthquake called a supershear
In a supershear, a pulse of energy can rip along the fault at up to 21,600 kilometres (about 13,000 miles) per hour -- many times faster than the speed of sound -- and can inflict immediate and potentially massive damage to buildings in the vicinity.
These quakes are not frequent and only occur on particular faults that are in a straight line, as this allows the pulse to be propagated without hitting an obstacle, rather as a car can speed along a straight road but slows at corners.
The devastating May 12 quake that hit China's southwestern province of Sichuan was not a supershear, but a conventional quake resulting from compression between two plates.
In a study published in science, researchers Michel Bouchon of France's National Centre for Scientific Research (CNRS) and Hayrullah Karabulut of Istanbul's Earthquake Research Institute pored over two supershear quakes that struck northwestern Turkey three months apart in 1999.
They also looked at a 2001 quake in Tibet that had a magnitude of 7.9 and produced a rupture of 425 kilometres, the longest ever observed, and at a supershear event in Alaska in 2002.
They found that supershears inflicted aftershocks in unexpected regions.
Compared with conventional, slower quakes, whose aftershocks are centred around the fault line, supershears unleashed aftershocks on nearby secondary faults and previously-dormant faults that had been awakened by stress from the rocketing pulse.
Being able to predict where aftershocks are likely to occur in a supershear-vulnerable zone could help save lives, although Bouchon, in remarks to AFP, commented " we need a lot more observations of large quakes to be sure" of where such spots could be.
The study is published in the US weekly journal Science.
© 2008 AFP
原始論文：
The Aftershock Signature of Supershear Earthquakes
Michel Bouchon and Hayrullah Karabulut
Science 6 June 2008: 1323-1325.
[Abstract]