The unusually strong 8.9-magnitude quake that shook Japan Friday strained Japan's civil and nuclear power infrastructure, U.S. researchers say.

University of Pittsburgh seismologist Bill Harbert said Pitt's seismograph detected the 8.9-magnitude quake for 3 hours, a rare magnitude and duration, a Pitt release said Friday.

Pitt's seismic station registered near-constant activity for the full 3 hours, he said.

Kent Harries, a Pitt professor of civil and environmental engineering, said while much of Japan's infrastructure is among the most disaster-resistant in the world, earthquake- and tsunami-resistant construction calls for entirely different principles.

For tsunamis, buildings need to be able to let water pass through -- such as beach houses on stilts -- while structures need a solid base to withstand an earthquake.

Although Japan has done well incorporating both requirements, Harries said, "the tsunami clearly seems to be the dominant source of destruction."

John Metzger, a Pitt professor of mechanical engineering and material science, said Japan's emergency procedures, modern reactor and plant designs, and lessons learned from Pennsylvania's Three Mile Island incident in 1979 mean Japanese reactors will likely remain stable.

Modern reactors permit a lengthy amount of time to respond, and it appears Japanese engineers were able to institute safety measures in a reasonable amount of time, Metzger, a nuclear engineer, said.