Re: [新聞] 臺灣地區的颱風可避免災難性的地震嗎？
※ 引述《Morbert.bbs@ptt.cc ()》之銘言：
: 預防重於治療--臺灣地區的颱風可避免災難性的地震嗎？
: http://www.tam.gov.tw/news/2007/200701/07010403.htm
: 來源：台北天文館天文新聞
: 美國華盛頓卡內基研究所（Carnegie Institution）Alan Linde、Selwyn
: Sacks及中研院地科所研究人員曾在12月中旬的自然（Nature）期刊中發表
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Nature並沒有這篇論文....
這個研究是在十二月AGU（美國地球物理聯合會）
研討會中（由中研院的劉啟清研究員）口頭發表，
Nature網站有一個專門整理重要研討會內容的部落格，
所以被Nature部落格寫出來。
（有台灣研究人員參與的研究，報導裡卻沒有提到名字，這樣有點令人難過...）
: 論文指出：颱風可能會引發地震。這篇報告並在自然期刊網站的部落格中
: 引發討論。
: 臺灣位於太平洋板塊、菲律賓板塊和歐亞大陸板塊的交界，其中菲律賓板
: 塊與太平洋板塊均為比重較大的海洋地殼，且向西移動，與比重較輕的歐
: 亞大陸板塊擠壓後，會向下沈降，隱沒在歐亞大陸板塊之下，而歐亞大陸
: 板塊受擠壓部分上升形成臺灣本島，為「聚合型」的板塊邊界。由於處在
: 如此特殊的地方，臺灣因而擁有各式各樣豐富的活躍地質風貌，成為地質
: 學者的研究天堂。
: http://www.tam.gov.tw/news/2007/200701/typhoon.jpg
: Linde與中研院地科所、臺灣地震科學中心等機構的研究人員於2003年開始
: 合作進行「板塊邊界觀測台計畫（Plate Boundary Observatory - Taiwan，
: PBO-T）」，在臺灣東海岸設置了3部應變觀測器（strainmeter），或利用
: GPS等儀器，觀察臺灣鄰近區域活躍的板塊邊界的各項變化，試圖找出為何
: 臺灣東海岸板塊邊界為何發生大規模地震的頻率不若其他類似地方的原因。
: 經過多年觀測後，研究人員提出一個全新的理論，認為由於臺灣經常會有颱
: 風通過，颱風為大氣壓力較低的地方，因而促使臺灣陸地壓力減輕，使得斷
: 層滑動速度加快；不過雖說「加快」，其實以人的觀點而言還是很慢，沒有
: 什麼危險性。因此在本質上，熱帶風暴可能會引起許多小型地震，並因小型
: 地震不斷發生，讓板塊邊界上的能量不致於累積得過大，因而鮮少發生大規
: 模的危險性地震。
: 雖然這個點子很不錯，不過似乎並不適用在全球。例如美國墨西哥灣就並非
: 位在板塊邊界這種高危險地震帶上，所以颶風的發生並不會對地震有何影響。
: 而日本的地質條件與臺灣差不多，就對這個颱風引發小地震、阻礙大地震發
: 生的想法頗感興趣，也打算加入相關研究。
: 資料來源：
: [台北天文館]
: http://www.tam.gov.tw/news/2007/200701/07010403.htm
: [板塊邊界觀測台計畫（Plate Boundary Observatory - Taiwan，PBO-T）]
: http://www.earth.sinica.edu.tw/research/research.htm
: [自然(NATURE)期刊的部落格]
: http://blogs.nature.com/news/blog/2006/12/agu_do_typhoons_cause_earthqua.html
:
Nature部落格中的原文是（中文報導似乎是直譯這篇文章）
Sometimes a couple of scientific instruments, in just the right place,
can trigger all sorts of new investigations. Take the three strainmeters
that the Carnegie Institution of Washington placed along the eastern
coast of Taiwan starting in 2003. Alan Linde and Selwyn Sacks, working
with their Taiwanese colleagues, were trying to figure out why the area
didn't seem to have as many large earthquakes as it should - being located
on the boundary of two tectonics plates and all.
Instead, the scientists arrived at a whole new theory. Typhoons passing
over the island, the team argues, release pressure on the land and allows
the faults there to slip at very high, but very slow and non-dangerous,
rates. In essence, tropical storms enable a lot of very small earthquakes
and prevent the large and dangerous ones.
It's a very cool concept that, unfortunately, may not apply other areas
of the world. The US Gulf Coast, for instance, is not at high risk of
killer earthquakes and thus could conceivably be saved by hurricanes.
But Japanese scientists are interested in extending the work to their
country, Sacks told me at his poster session this morning.
"This is a big surprise for us," he said. "It's the kind of finding that
is driven by data, not by insight."
這是這個研究在AGU研討會的摘要：
As part of a cooperative program between Academica Sinica, Taiwan,
and Carnegie Institution of Washington a small network of Sacks-Evertson
strainmeters has been installed in eastern Taiwan, starting in 2003. The
program focuses on providing data that will complement GPS data sets in
aiding improved understanding of the rapid and complex tectonic
deformation of the area. The initial data from all sites show the
standard characteristics of good quality: tidal signals with very high
signal to noise ratio and large (～10,000 counts on 24 bit ADC system)
amplitudes; strains trending into conpression with rates that decrease
exponentially with time and earthquakes clearly recorded. Additionally
the instruments have recorded a number of slow strain changes with
durations ranging from about an hour up to a few days; we interpret these
signals in terms of slow earthquakes. All of the slow events identified
to date occur at the times of typhoons passing over or very close to the
study area, but not all typhoons are associated with slow strain events
(e.g. 9 typhoons in 2004 were accompanied by 5 slow events). Seismicity
for the area deliniates a roughly north-south striking steeply dipping
(to the west) zone with reverse slip; the shallowest extent of the zone
is approximately 10 km inland. We look for source solutions consistent
with that tectonic setting. The slow events exhibit a considerable range
of amplitude and complexity; small, short amplitude events have a quite
simple and smooth waveform; the longest (2 days) and largest (100 to 350
nanostrain at 3 sites) has waveforms with a lot of structure. The
similarity among the stations (located in an isosceles triangular array
with spacing ~ 10 km and 4 km) is indicative of rupture propagation
of a slow slip source (equivalent magnitude about 5), propagating up dip
and from south to north. Typhoon activity produces a large increase in
short period (~ sec) energy so it is not possible to determine
whether these slow events are accompanied by non-volcanic tremor, as has
been reported for the Nankai subduction and Cascadia slow events. We
hyothesize that the slow earthquakes are triggered by the typhoon
activity due to lower air pressure over land reducing the normal force
on the fault zone.
所以他們提出的理論是
颱風的低壓降低斷層面的正向力(normal force)
-> 引發slow earthquake
（-> 斷層能量得以釋放，降低大地震發生的機會?
這點在摘要裡沒提到，也許口頭發表時有說到，所以部落格裡才會寫出來）
重點是在slow earthquakes，這指的是斷層面緩慢但持續時間較長的錯動，
（可持續數小時甚至數週，產生的震波很不明顯，
除了特殊儀器strainmeter或GPS觀測得到之外很難察覺）
跟一般所說的地震很不一樣。
摘要裡提到，台灣東部一年經由slow earthquake釋放的能量，
約等同於一個規模五的地震，
也就是說，累積一百年的話，颱風可能幫助釋放一個規模七地震的能量。
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