A strong earth tremor yesterday rocked the northern city of Tangshan, where a devastating earthquake in 1976 killed more than 200,000 people. The quake, measuring 4.7 on the open-ended Richter scale, hit Tangshan, in Hebei province, at 10.47 am. Xinhua said residents and local officials reported the quake had shattered windows, toppled walls and caused cracks in buildings. The seismic activity was felt 175 kilometres away in Beijing and Tianjin. A State Seismological Bureau official said the quake was an 'aftershock' of the 1976 tremor, which measured 7.8 on the Richter scale. A spokesman for the Hong Kong Observatory, which recorded the latest seismic wave, said an aftershock 20 years later was not unusual. The latest quake had been predicted in a monthly forecast report issued by the state bureau on March 27, following the installation of new equipment. 'Buildings in Tangshan are built to sustain seven or eight on the Richter scale. Most of them, except the older ones, are fine,' a bureau official said. He added that there was little chance of a stronger quake in the near future. Beijing said recently it was building a 135 million yuan (HK$126 million) satellite-based earthquake monitoring system to predict tremors more accurately.