Download Taiwan Moves Closer to Mainland, Pulled by Forces That Molded Its

Taiwan Moves Closer to Mainland, Pulled by Forces That Molded Its Mountains
By INGFEI CHEN
Published: April 18, 2006, New York Times
Politically, Taiwan's relationship to Beijing could be characterized primarily as a rift borne of
defiance on one side and menacing rebuke on the other. But geologically, the small island of
Taiwan appears to be on a collision course with mainland China. Over millions of years, that
is.
Francis Wu and his colleagues this month will deploy seismometers around Taiwan, with its
rising peaks, to learn more about mountain building.
Multimedia
Graphic: An Island on the Move
Millimeter by millimeter, the same colossal forces that molded Taiwan's steep mountains —
and that unleash its earthquakes — are narrowing parts of the Taiwan Strait, bringing the
island ever closer to the mainland.
Now an international coalition of scientists from the United States, Taiwan and Japan are
planning to delve into those mountain-building processes. And despite friction between
Taipei and Beijing, the project's leaders have quietly requested assistance from mainland
Chinese geologists. If officially approved, the researchers say, the collaboration would be one
of the biggest formal cross-strait scientific partnerships. Such joint endeavors remain rare.
Known as Taiger, the $5 million study will use seismic monitoring on land and sea to create a
three-dimensional snapshot of Taiwan —the geological equivalent of an M.R.I. scan, said
Francis Wu, a geophysicist at the State University of New York, Binghamton.
Scientists have previously used the same techniques to make 3-D images of many mountain
ranges. But because the Taiger survey will be of much higher resolution, it will provide the
most detailed map yet of a mountain belt — from its 12,900-foot peaks to its roots about 18 to
30 miles underground and deeper, to earth's upper mantle, 370 miles underground, Dr. Wu
said.
This month Dr. Wu and his colleagues will deploy a first set of seismometers along three
transects spanning the island' s width. For two years the instruments will record vibrations
from nearby and distant earthquakes.
Because the shock waves travel at different speeds through different materials, they reveal
much about the rock structures within the earth's crust. In November, the researchers will
bury another 1,000 seismometers placed at 100-meter intervals, to detect controlled
explosions.
The mapping will continue in spring 2008 in the waters around Taiwan. The American
research ship Marcus Langseth will shoot gigantic air bubbles underwater, creating seismic
waves that travel into the sea floor and bounce back. Strings of sensors towed by the ship and
a grid of seismometers on the ocean bottom will monitor the experiment.
The survey builds upon a rich history of research exploring Taiwan's topography. Since the
1970's, the island has been a natural laboratory for probing how collisions between tectonic
plates, the vast interlocking slabs that make up the earth's crust, gave birth to mountain belts.
"Taiwan is one of the fastest rising mountains in the world," Dr. Wu said.
The island's peaks are rising roughly two or three centimeters a year. That may sound about
as thrilling as watching your toenails grow, but for Dr. Wu and others who ponder
geodynamic events that unfold over hundreds of millions of years, it is more like the
Indianapolis 500.
Taiwan popped up in the Pacific Ocean four million to five million years ago when the
Eurasian plate —where mainland China is — slid under an ancient chain of volcanic islands
sitting on the neighboring Philippine Sea plate. Sometime later, the two plates somehow
reversed roles at the north end of Taiwan: there, the Philippine slab slides under the Eurasian
slab.
The Himalayas, an estimated 50 million years old, are also growing rapidly and are of interest
to scientists. But Taiwan's smaller scale (roughly the size of Vermont) and greater accessibility
make it easier to study, Dr. Wu said.
The island is not only seismically active; it also undergoes substantial erosion from monsoons,
in a process believed to influence how quickly mountains rise, said Kip Hodges, a geologist at
the Massachusetts Institute of Technology. Taiwan is "a very good place to study this kind of
collisional behavior," Dr. Hodges said.
In fact, the classic theory of how mountains evolve came from research on Taiwan, said
Timothy Byrne, a geoscientist at theUniversity of Connecticut and a consultant for the
Taiger study. In the early 1980's, John Suppe, a Princeton geologist, and his colleagues
calculated that mountains form in subduction zones just as a bulldozer pushes into a pile of
sand, creating a wedge-shaped mound in front of its shovel blade.
For Taiwan, the bulldozer blade is the Philippine plate, scraping the top of the Eurasian plate.
"That's a pretty good analogy for the top 10 or 15 kilometers of Taiwan," Dr. Byrne said. "It's
not grains of sand but small blocks of the earth's crust that are breaking apart."
But questions remain over how much the bulldozer model applies at greater depths, Dr. Byrne
said, particularly under the midsection of Taiwan. Dr. Wu, for one, speculates that the
Eurasian slab does not actually subduct there but instead has crumpled up against the
Philippine plate, edge to edge, like two cars in a head-on collision.
By answering some major questions about the deep structure, the new study could improve
the understanding of mountain building, Jacques Angelier, a veteran French investigator of
Taiwan geology, said in an e-mail message. Dr. Angelier, who is not involved in the mapping
study, works at the Villefranche Oceanological Observatory of the Pierre & Marie Curie
University.
A clearer picture of Taiwan's plate dynamics could also help define its potential seismic
hazards, said Chao-Shing Lee, a geoscientist at the National Taiwan Ocean University in
Keelung, another study collaborator. Mountain making causes earthquakes, like the
7.6-magnitude temblor that struck Taiwan in 1999, killing 2,400 people.
Historical accounts show that huge quakes in the Taiwan Strait have set off deadly tsunamis,
including one that swamped Keelung, at the island's north tip, in 1867. And scientists believe
that a tidal wave set off by a quake destroyed the Quanzhou seaport in South China in 1604. A
tsunami generated in the strait could reach Taiwan and the mainland in 20 minutes to a
couple of hours, Dr. Lee said.
Since geology's perils pay no heed to politics, Dr. Wu and Dr. Lee visited the China Geological
Survey in Beijing in November to discuss its potential participation in the Taiger study.
Mainland geologists said they could use their ships to help with the air bubble experiments in
the strait, said Dr. Lee, who is a member of the science and technology council that advises the
president of Taiwan. "We can split the task but cooperate, and then we share the data," he
said.
Rui Gao, a geophysicist at the Chinese Academy of Geological Sciences, said in an e-mail
message that the collaboration would "benefit people on both sides of the strait."
Political differences should not prevent scientific partnerships, he said.
Although Taiwanese and Chinese researchers routinely work together individually, large-scale
official partnerships are still rare. In an act of geodiplomacy, the geoscientists are now
delicately moving to persuade their respective governments to approve the Taiger study
collaboration.
But success seems uncertain with continuing political tension. Taiwan's president persists in
pushing for independence; Beijing, which last year passed legislation outlawing Taiwan's
secession, has in the past vowed to reunify it with China by force if needed.
Meanwhile, as the Philippine and Eurasian plates converge at eight centimeters a year, the
island's mountain zone keeps gradually growing on its west side. Some parts of the strait are
becoming shallower and narrower, said Dr. Byrne of Connecticut. It's impossible to predict
how the plate interactions will change, but if current patterns hold, he said, in a few million
years "Taiwan Strait will be gone, will be dry land."
Will the island and the mainland ultimately reunify? Asked the question at a recent scientific
meeting in San Francisco, Dr. Lee smiled enigmatically and chuckled. "If the Chinese can be
that patient," he said.