Quake alert level for Zhaotong was raised earlier this year
National researchers raised the alert level for Zhaoting earlier this year after academics said it could suffer a magnitude 7 tremor
The national earthquake monitoring centre said it raised the risk level for Zhaotong, where more than 400 people died in a tremor on Sunday, from a magnitude 6 to a magnitude 7 this year.
The higher alert came after academics warned last year a fault line running through the area had stored up a "tremendous amount" of energy, and nearby counties could be hit by a quake as strong as 7.4.
Zhaotong city sits along the Zhaotong fault, one of the main fault lines for northeastern Yunnan province. The city has been listed as a "key area" for monitoring for the past decade, said a staff member of the provincial earthquake administration.
The dangers were highlighted in research published last year by experts from the State Key Laboratory of Earthquake Prediction under the China Earthquake Administration. The area contained a "locked fault" segment, the academics wrote. Without regular seismic activity, a "tremendous amount" of energy can build up over time, possibly centuries, before being unleashed in a major earthquake, according to the US Geological Survey.
The quake that struck on Sunday afternoon was a magnitude 6.5, and came at a depth of 12km. More than 2,370 people were injured and 80,000 homes collapsed, according to Xinhua.
"The state authority raised the earthquake alert level for the region from magnitude 6 to magnitude 7 this year", Jiang Haikun, director of the earthquake prediction office at the China Earthquake Networks Centre, told the South China Morning Post. Local authorities had been ordered to reinforce old buildings in the wake of the alert, the provincial earthquake administration said. But the region's heavy rain and the complex terrain were also to blame for the heavy casualty toll.
Jiang said the academic paper was "background research" on the fault zone, not a prediction of a major earthquake. "China has a lot of locked fault segments … Of course we have been following up the academic report. But when we say 'long-term' in earth sciences, we are talking about decades," he said.
The region has seen six earthquakes of magnitude 5 or above between 2003 and 2012, said Chen Guihua, a researcher at the Institute of Earthquake Science under the state earthquake agency.
Xu Xiwei, vice-president of the institute, said monitoring devices in the region had recorded irregular geological activities over the past few years. "The problem is scientists have not found out which irregular activities constitute precursors to earthquakes. The mechanisms are not fully understood," Xu said.
He called on the authority to set up more monitoring devices in the country's earthquake-prone zones to collect data on irregular geological activities.
"It's like looking for the treatment for cancer. Doctors would never find a cure for the disease unless they have done enough case studies, which is the same for us," he said.