and experts say the nankai trough is overdue for a big jolt. if a earthquake hit this area, it could produce what scientists called long period ground motion. that means ground movement during an earthquake that causes vibrations that last a long time. earthquakes causing short quake ground vibrations did not generate intense swaying. but long period ground motion causes intense swaying in high-rise buildings. inside, there's lots of damage. the march 2011 earthquake that hit northern japan did this in this is a video from a restaurant in a high-rise. the skyscraper in tokyo swayed slowly. the megaquake generated long period of motion. the swaying does not die down even in areas far from the epicenter. it is a huge concern for this disaster relief expert. >> translator: there can be more than 1,000 people in each skyscraper. several million people could be affected by the swaying. if they are hit by heavy objects, it could kill them. precautions must be taken. >> reporter: and some cities are already taking those precautions. japan's tourist bu