SCIENCE OBSERVER
Looking for Dr. Pangloss
David Schneider
On Christmas Day 2004, early in the afternoon, geophysicists at the
Pacific Tsunami Warning Center in Ewa Beach, Hawaii, realized that a
powerful temblor had occurred just west of the Indonesian island of
Sumatra—one they feared might cause a significant tsunami when
the disturbance reached shore. Unlike the waves that propagate
through the solid earth, tsunamis can take hours to travel between
their source region and some of the faraway places they damage. So,
in principle, early detection and the dissemination of warnings can
save lives. Yet the geophysicists at the Pacific Tsunami Warning
Center found themselves ill-prepared to alert officials in nations
bordering the Indian Ocean. One reason is that the network of tide
gauges and ocean-bottom pressure sensors these geophysicists rely on
is, for the most part, limited to the Pacific, so they did not have
the means to check whether a tsunami had indeed been generated.
Given the huge number of people that perished in this horrific
disaster, it seems fitting that world leaders have called for a
tsunami warning system, presumably one similar to that in the
Pacific, to be set up in the Indian Ocean. But is this really the
best response?
One concern is that such a move does nothing to improve tsunami
readiness in communities bordering the Atlantic, an ocean that is
typically ignored in this context. Big tsunami-generating
earthquakes are most likely to take place in the Pacific, which is
surrounded by subduction zones (places where two tectonic plates
grind together as one plunges downward), or to a lesser extent in
the Indian Ocean, which is bordered by the Sumatran subduction zone
on the east. But, in fact, the Atlantic also has regions where
subduction takes place. One is situated to the east of the Caribbean
Sea, just outside the arc of the Antilles islands. Subduction also
takes place to the east of the South Sandwich Islands, which are
found in the South Atlantic. Although these earthquake-prone zones
are smaller than those bordering the Pacific, neglecting their
potential to cause destructive tsunamis would be
irresponsible—especially given that an even more subtle area
of subduction in the Atlantic produced a devastating tsunami in the
not-so-distant past.
On November 1 of 1755—All Saint's Day—at about 9:30 in
the morning, a powerful earthquake struck in the easternmost
Atlantic. The shaking was felt throughout Europe, with the most
destructive effects focused along the coast of the Iberian Peninsula
and Morocco. Lisbon in particular was hard hit, and many of its
250,000 residents lost their lives. Most perished in the collapse of
buildings. Others succumbed to the fires that immediately broke out.
Some sought refuge from the toppling buildings and growing inferno
along the city's waterfront, only to become victims some 40 minutes
later when the tsunami reached shore. The waves grew about 6 meters
tall in Lisbon and reached a height of more than 15 meters at Cape
San Vicente in southwest Portugal. They ran up to 10 meters or more
when they hit the coast of Morocco.
Casualty estimates vary considerably, but it is generally thought
that the earthquake, fire and tsunami together killed some 60,000
people. This death toll amounted to a substantially greater fraction
of the world's population (then probably about a half a billion)
than did the toll in the recent Indian Ocean calamity. The scale of
this 18th-century disaster and its devastating impact on
Lisbon—then an important center of
Catholicism—engendered much philosophical questioning about
the nature of divine justice. It inspired, for example, Voltaire's
satirical novel Candide, in which the titular protagonist
is constantly asking his tutor, the ever-optimistic Dr. Pangloss,
about how to reconcile the woes of the world with the existence of a
benevolent God.
So the lesson from history is clear enough: Subduction-zone
earthquakes in the Atlantic can also create destructive tsunamis.
Another reason not to exempt the Atlantic from future planning is
that dangerous tsunamis are not all triggered by large
subduction-zone earthquakes. In 1929, for example, a relatively
modest quake triggered an undersea landslide on the continental
slope off Canada. That landslide in turn gave rise to a tsunami,
which killed 29 people. And marine geologists are aware of similar
spots on the other parts of the continental shelf that must have
raised even more havoc in the distant past. In 2000, Neal Driscoll
of Woods Hole Oceanographic Institution and two colleagues published
a study of the sea floor off the coasts of Virginia and North
Carolina, suggesting that this area of the continental slope may be
subject to failure, something that could conceivably spawn a
devastating tsunami along the Eastern Seaboard of the United States.
Is the proper answer, then, to expand the tsunami-warning system now
in place in the Pacific to the whole planet? Perhaps. But this
strategy doesn't make for a complete solution. The problem, as many
commentators have noted, is that registering the threat and
communicating warnings to country officials does not guarantee
appropriate action on the ground. The Indian Ocean disaster provides
an illuminating example: After the quake struck, the geophysicists
in Ewa Beach sent an e-mail warning to authorities in Thailand, who
had given them no other contact information. But the message was
ignored. (Accounts differ: Some say the critical e-mail was never
read; others contend that Thai officials were fearful of
jeopardizing the tourist trade and decided not to issue a warning,
expecting that it would turn out to be a false alarm.) But more
vigilance on the part of civil-defense officials may not be the
answer either. In Japan, where tsunami warnings are effectively
communicated, the citizenry tends to get jaded—in a recent
episode in Hokkaido, only half the people warned to evacuate the
danger zone bothered to leave.
What then must we do? Better education about tsunamis for anyone
living close to the ocean would probably go a long way—even
without any formal warning system. Steven Ward, a geophysicist and
tsunami modeler at the University of California, Santa Cruz, says
that "the first arrivals are not usually all that big." He
further points out that the period of these waves can be 10 or 15
minutes, meaning that after observing unusual changes in the level
of the ocean" you'd have time either to walk to high ground or
climb up a good, strong building."
Expanding on the Pacific warning system would, of course, be helpful
too. But in doing so, planners should pay considerable attention to
the inherently weak link between warning and response. The system
shouldn't allow lackadaisical authorities to veto alarms by whim;
nor should it be set up with such sensitive triggers that
populations eventually become complacent. To fix such problems,
geophysicists and civil-defense planners will probably need to take
heed of psychology as much as technology. In the best of possible
worlds, clever minds could be expected to come up with a system that
always worked flawlessly. But, as Voltaire was so good at pointing
out, ours is far from the best of all possible
worlds.—David Schneider