地質學家去年已定位出引發川震的斷層 - 地球科學討論

ENS一篇蠻用心的英文報導，以下摘錄重點


Scientists Identified Earthquake Faults in Sichuan Last Year
http://www.ens-newswire.com/ens/may2008/2008-05-18-01.asp


Research published by earth scientists last summer in the international
journal "Tectonics" found that geological faults in China's Sichuan
Basin "are sufficiently long to sustain a strong ground-shaking
earthquake, making them potentially serious sources of regional seismic
hazard."

The international team of Chinese, British, Swiss and American scientists
mapped and analyzed a series of geologically young faults that cross
Sichuan province like recently healed scars.

The team mapped the densely populated Sichuan Basin and adjacent
mountains using a technique known as tectonic geomorphology. With this
technique, scientsts can demonstrate changes in ground movement over time,
such as offset river channels, disrupted floodplains, abnormally shaped
valleys and uplifted landscape features.

Two long faults in particular, running almost the entire length of the
Longmen Shan range, showed clear evidence of slip during the last few
thousands, and in some cases, the last few hundreds, of years, they found.

One of these faults is "likely" to be the one that gave rise to the 7.9
magnitude May 12 earthquake, the scientists said today in a statement.

"Exactly why the Longmen Shan are here is a mystery. Unlike the Himalaya,
which form the southern boundary of Tibet and whose faults chatter
continuously with small earthquakes, faults in the Longmen Shan, remnants
perhaps of geological events hundreds of millions of years ago, have
historically only produced earthquakes up to magnitude 6," the authors
write.

Geomorphological evidence, described in the "Tectonics" paper, suggests
that the mapped faults are very steep with dominantly lateral or strike-
slip displacements taking place over time scales of thousands to hundreds
of thousands of years.

This contrasts with shorter-term measurements using Global Positioning
Systems which suggest a greater proportion of thrust or shortening
displacement than lateral displacement.

The observations of seismologists at the British Geological Survey
suggest both things - more thrust in the southwest, nearer the epicenter
of the quake, and more strike-slip toward its direction of propagation,
the northeast.


To read the paper, "Active tectonics of the Beichuan and Pengguan faults
at the eastern margin of the Tibetan Plateau," click here.
http://www.geography.dur.ac.uk/documents/densmore/densmore_etal07.pdf


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