Map Courtesy of Earth Consultants International
A seismic fault runs right through a lake between the Panama Canal's two existing locks, close to the third set.

The quality standards set for the locks for the Panama Canal's Third Lane Expansion are enormously high, partly due to seismic risk. While the danger posed by earthquakes is perceived to be low, studies by the Panama Canal Authority (ACP) found evidence of an active fault running next to the new locks on the Pacific side of the canal.

A program to examine the canal's seismic vulnerability was initially launched in 1994. In 2003, a Seismic Advisory Board was created to continue these efforts but also provide input for the then-proposed expansion project. The board's research found a fault running through the Pacific-side expansion project was positively linked to a temblor 400 years ago, believed to be of magnitude 7 or greater.

The initial design of the Pacific locks required they withstand peak ground acceleration of 0.3g. That was reduced to 0.5g after the findings of the geotechnical studies. The Atlantic-side locks initial standard of 0.5g was reset to 0.3g, roughly the degree of shaking associated with an earthquake in the magnitude-8 range.

Maximilliano De Puy, the ACP's geotechnical manager, says the strict standard is dictated by a trio of factors: the proximity of the Pacific locks to the Pedro Miguel fault, the need to ensure a seismic event would not substantially interrupt canal traffic and the locks' expected 100-year life span.

The ACP turned to MWH Global to augment the locks' design to handle a potential major seismic event in close proximity to the canal. The group assembled a design team that included outside experts and consultants to create a 3D model of the locks and run seismic tests.

The model of the lockheads and gates themselves took seven months to develop and more than 70 hours to run each test load, says MWH's project manager, Michael Newbery. Furthermore, each lockhead required a minimum of 14 seismic load tests. Models of all the lock chambers were also developed. "It was a tremendous amount of computing," Newbery says.

The Borinquen Dam will be part of the access channel connecting the Pacific locks and the canal's main navigation channel, separating it from the Miraflores Lake. It sits atop the Pedro Miguel fault. The ACP opted for rockfill embankment with a central earth core. The structure is designed to sustain a three-meter horizontal displacement and a 0.5-m vertical displacement.

Concerns about seismic activity on the canal were aired as early as 1906 by Brig. Gen. Henry L. Abbot, a member of the American and Foreign Board of Advisory Engineers advising Congress on the original canal proposal. Abbot objected to a lock canal due to seismic risk.

The largest documented earthquake in Panama's history was an estimated magnitude-7.6 temblor on Sept. 7, 1882, that caused 50 deaths and destroyed many buildings in Colòn. The epicenter of the quake was in the Caribbean Sea, about 50 miles from the coast of Panama. The significant amount of historical documentation of this event was one reason the Caribbean side of the isthmus has been more associated with seismic risk.

Another quake, on May 2, 1621, destroyed almost all the houses in the country and is believed to have been magnitude 7 or greater. Previously, this event was thought to have had an epicenter on the north of the isthmus, but research has revealed it was more likely along the Pedro Miguel fault.