Remote triggering of fault-strength changes on the San Andreas fault at Parkfield
Taka'aki Taira1, Paul G. Silver1,4, Fenglin Niu2 & Robert M. Nadeau3
1. Department of Terrestrial Magnetism, Carnegie Institution of Washington, District of Columbia 20015, USA
2. Department of Earth Science, Rice University, Houston, Texas 77005, USA
3. Berkeley Seismological Laboratory, University of California, Berkeley, California 94720, USA
Deceased.
4. Correspondence to: Taka'aki Taira1 Correspondence and requests for materials should be addressed to T.T. (Email: taira@dtm.ciw.edu).
Abstract
Fault strength is a fundamental property of seismogenic zones, and its temporal changes can increase or decrease the likelihood of failure and the ultimate triggering of seismic events. Although changes in fault strength have been suggested to explain various phenomena, such as the remote triggering of seismicity, there has been no means of actually monitoring this important property in situ. Here we argue that 20 years of observation (1987–2008) of the Parkfield area at the San Andreas fault have revealed a means of monitoring fault strength. We have identified two occasions where long-term changes in fault strength have been most probably induced remotely by large seismic events, namely the 2004 magnitude (M) 9.1 Sumatra–Andaman earthquake and the earlier 1992 M = 7.3 Landers earthquake. In both cases, the change possessed two manifestations: temporal variations in the properties of seismic scatterers—probably reflecting the stress-induced migration of fluids—and systematic temporal variations in the characteristics of repeating-earthquake sequences that are most consistent with changes in fault strength. In the case of the 1992 Landers earthquake, a period of reduced strength probably triggered the 1993 Parkfield aseismic transient as well as the accompanying cluster of four M > 4 earthquakes at Parkfield. The fault-strength changes produced by the distant 2004 Sumatra–Andaman earthquake are especially important, as they suggest that the very largest earthquakes may have a global influence on the strength of the Earth's fault systems. As such a perturbation would bring many fault zones closer to failure, it should lead to temporal clustering of global seismicity. This hypothesis seems to be supported by the unusually high number of M 8 earthquakes occurring in the few years following the 2004 Sumatra–Andaman earthquake.
http://www.nature.com/nature/journal/v461/n7264/full/nature08395.html
http://www.nature.com/nature/journal/v462/n7273/full/nature08545.html
新理論 地層壓力轉移「震群」竄全球
更新日期:2010/03/05 02:26 王嘉源／綜合報導
中國時報【王嘉源／綜合報導】
最近全球發生強烈地震的頻率異常地高，台灣四日上午也出現地震，是否完全純屬巧合，引起討論。傳統看法認為，地理位置相距遙遠的大地震不至於有所關聯，但也有科學家指這是所謂的「震群」（earthquake clusters）現象，全球各地強震可能和台灣高雄縣甲仙地震有關。
《夏威夷現在新聞》（HawaiiNewsNow）網站四日引述美國內政部地質調查所報導，一個地方發生強震後，可能出現骨牌效應，產生「震群」現象。因為大地震造成地層壓力轉移，繼而出現一連串地震。
看似距離遙遠 仍有骨牌效應
一月十二日，芮氏規模七．○強烈地震重創加勒比海國家海地。接著二月廿六日，日本琉球附近海域發生同樣規模的強震。翌日，南美智利即發生八．八級大地震。再來就是台灣南部高雄在四日出現六．四級地震，同一天幾小時前智利還有規模五．九到六．一的餘震。根據傳統看法，地理位置相距十分遙遠的地震不能相提並論，但這次不到兩個月內發生如此多強烈地震，令科學家不敢斷言純屬巧合。
去年九月，英國《自然》周刊發表的一項研究報告指出，二○○四年十二月印尼蘇門答臘發生引起大海嘯災難的芮氏規模九．一強震，也對加州「聖安地列斯斷層」（San Andreas fault）造成影響。
美國地震學家發現證據顯示，該次大地震及後來蘇門答臘又出現的一連串地震，造成距離八千公里之外的聖安地列斯斷層頻頻鬆動，三個月內小地震不斷；斷層區某些區塊的裂縫內充滿液體，液體外流並鬆動斷層，因而增加地震發生的可能。
http://tw.news.yahoo.com/article/url/d/a/100305/4/21h8k.html
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