This week's staggering cocaine bust in Philadelphia is another sign that traffickers are turning to East Coast seaports as a result of increased law enforcement pressure along the country's southwest border.

Federal law enforcement officials raided a container ship at Philadelphia's port and discovered 33,000 pounds (15,000 kilograms) of the illicit drug, one of the largest caches ever intercepted on U.S. shores. Federal officials estimated it had a street value of more than $1 billion.

It was at least the third major bust in Philadelphia and New York since February.

Nicholas Magliocca, a University of Alabama researcher, says that "as soon as interdiction puts pressure on one place, it just pops up somewhere else."