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Another problem will be the serious difficulty of

identifying explosions as nuclear tests.  At lower yields,

the number of nonnuclear events of similar size increases

(e.g., mining explosions and earthquakes on land, explo-

sions for geophysical exploration, volcanoes at sea, mete-

orite impacts in the atmosphere).  Nonnuclear events

increase the total number of events to be processed by a

verification system, and a small percentage of them gener-

ates signals similar to those expected from nuclear explo-

sions.  This, too, increases the difficulty of identifica-

tion.

In addition to its technical limitations, the IMS has

other problems.  The fact that stations monitoring some

nations will be within their own borders offers the possi-

bility that IMS data could be manipulated, or that the

stations could be shut down during a test--just as

Pakistan turned off a key seismic station within its bor-

ders when it conducted a nuclear test in May 1998.  Some

of the stations monitoring China will be within China;

some monitoring Russia are within Russia.  Hypothetically,

either nation could ensure that the station or stations

would not be working during the time of a test, thus

depriving the IMS of key data.  Shutdowns would not neces-

sarily appear unusual because, inevitably, there will be

times when the stations are not functioning properly.

The technical problems with CTBT verification are com-

plicated by another difficulty that will not be addressed

in detail here: the problem of gaining political consensus

for a response when noncompliance with the treaty is sus-

pected.  In the case of the current nuclear testing mora-

torium, there have been indications that Russia may have

conducted low-yield nuclear tests.  Yet there have been no

U.S. protests or inquiries.  Shortly after an incident in

January 1996, former secretary of defense William Perry

told Congress that there had been suspicious activity at

the Russian test site, but there was no follow-up of con-

sequence.15   There are numerous possible explanations for

the lack of concern, including fear of setting the stage

for resumption of U.S. testing, fear of embarrassing

President Yeltsin, and fear of upsetting the then-ongoing

negotiations on the CTBT.  Regardless of the reason, it is

clear that challenging nations suspected of illegal behav-

ior can be politically very difficult.

Other Nations May "Legally Cheat"

The inability to verify the CTBT is complicated by

yet another factor: the CTBT does not define what consti-