A strong earthquake with a magnitude of 5.9 jolted northern Japan on Monday in the latest aftershock to hit a region struck by a deadly tremor last month. The earthquake struck at 11:15 a.m. (9:15 p.m. EST Sunday) and its focus was near those of the other quakes that have hit the Niigata region, the Meteorological Agency said. A series of smaller quakes followed. No tsunami warning was issued. Public broadcaster NHK said a 68-year-old construction site worker was in hospital for treatment after being buried in a landslide and six people were slightly injured when they were hit by parts of a wall that collapsed. High-speed bullet trains in the area were temporarily halted and parts of local highways closed for safety checks, NHK said. The Niigata region, 150 miles north of Tokyo, was hit by a 6.8 magnitude earthquake on Oct. 23 that killed at least 39 people. That was Japan's deadliest quake since one with a magnitude of 7.2 killed more than 6,400 in Kobe in 1995. "It's scary. They keep coming, so you can't relax," one woman told NHK following the aftershock. The frequency of aftershocks has eased, but the Meteorological Agency has warned that more tremors of a similar scale could continue for about a month. The magnitude is measured by a technique similar to the Richter scale but adjusted for Japan's geological characteristics. Seismologists have said that the initial quake had occurred in a "seismic gap" -- part of an active fault that had experienced little or no seismic activity for a long period, causing stress to build up and making an earthquake more likely. They have said there were still areas in the fault where the stress remained to be released, meaning aftershocks could occur in such places. Earthquakes are common in Japan, one of the world's most seismically active areas. Japan accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater. **PHOTO CAPTION*** Japanese children crawl down on the floor at an elementary school in Kawaguchi town, northern Japan as a strong earthquake with a magnitude of 5.9 jolted the area November 8, 2004, the latest aftershock to hit a region struck by a deadly tremor last month. (Reuters)