An Yin of the University of California in Los Angeles and his colleagues analysed modern and historical records of earthquakes in northern China. Mapping their locations revealed a 160-kilometre-long fault segment running through Tianjin, roughly 100 kilometres southeast of Beijing. This area has not experienced a major tremor for about 8,400 years, and the authors estimate that a quake of roughly magnitude 7.5 is either overdue or will strike in the next 2,000 to 3,000 years.Given the region’s complex fault structure, however, other factors could explain the lack of major earthquakes, such as multiple smaller quakes releasing energy from the fault.