- A new study reveals a worrisome quake history in Panama.
- The revised quake threat comes as the canal is being expanded.
- Of more seismic concern than the canal is Lago Gatun and Panama City.
Two large earthquake faults could expose the Panama Canal to serious shaking and perhaps damage, say geologists who have uncovered 1,400 years of fault ruptures in the area.
Worse than that, however is the threat to Panama City, which houses a third of the nation's population -- many in buildings that could become death traps in a major quake.
The threat comes from the Limon and Pedro Miguel faults in Central Panama which have ruptured both together and separately in the past. A team of seismologists sorted out the history of the past quakes by deciphering extensive changes in the landscape -- like streams offset several feet or meters -- and shifts in at least one historical road.
The analysis on the seismic history and hazards of central Panama was published in the latest issue of the Bulletin of the Seismological Society of America. The study was done at the behest of the Panama Canal Authority, which is in the process of expanding and upgrading the canal so it can handle much larger ships carrying far more cargo.
The Panama Canal was originally built from 1904 to 1914, when cargo ships were a a lot smaller than today. The new canal, which is scheduled for completion by 2014, will allow much larger ships to traverse the 48-mile-wide isthmus separating the Pacific from the Caribbean and Atlantic waters.
"An earthquake (in 1621) offset the Camino de Cruces that the Spanish used to get gold to Panama City," said Thomas Rockwell of San Diego State University. The centuries-old cobblestone road was cut by one of the faults and offset about 10 feet. A similar sort of offset could cross the canal itself.
Paleoseismic investigations by Rockwell and his colleagues show that both the Limon and Pedro Miguel faults are active, recur frequently with large quakes and can shift the ground from 1.5 to 3 meters (4.9 to 9.8 feet).
The oldest rupture the seismologists found was on the Pedro Miguel fault, and appears to have been in 455 A.D. However, the last Pedro Miguel quake and the third Limon fault rupture are both dated to about 700 A.D. This could mean both faults unzipped at the same time.
"There was a general perception before this (study) that there weren't any earthquakes," said Rockwell. This was despite the fact there was a magnitude 7.9 quake in 1882, which also created a tsunami. "They have historical earthquakes (but) that just wasn't part of the thoughts of engineers."
Geologically speaking, there is every reason to expect earthquakes in Panama, since the land there was created by the ongoing collision of tectonic plates, Rockwell explained. The new assessment will likely be used in the design of the new canal locks. But what really worried Rockwell and other seismologists is Panama City and the large lake, Lago Gatun, in the middle of the isthmus, which is held back by two aging dams.
"This is a very real issue," said seismologist Mary Lou Zoback. "There have been hints at this (quake history and threat) but we hadn't a comprehensive picture. I'm quite honestly much more concerned about Panama City. It is a very large fault and has a potential for a very large earthquake."
Panama's population is about 3.3 million. About 1.2 million of those people live in Panama City, Zoback pointed out. Many live in homes made with heavy, un-reinforced blocks on steep hillsides that could easily collapse in a strong earthquake, she said.
Then there is the huge Lago Gatun, which supplies the water to the locks that make the canal function.
"The real concern is if you breach one of the dams and drain the lake, it would take 10 years to refill it," said Rockwell. "So it's not just a matter of repairing. This would ruin Panama's economy."