Plethora of aftershocks normal, experts assure

As of Thursday morning, over 200 aftershocks had occurred in Yibin, Sichuan province, after the city was struck by a magnitude 6.0 earthquake on June 17. Experts said the frequency of aftershocks, though comparatively high, is still within normal range.

The special geological conditions in the region, which boasts no big seismological faults but many small and widespread ones, are to blame for the frequent aftershocks. Those small faults could have easily been made active after the major quake, the experts said.

According to the China Earthquake Networks Center, 225 aftershocks above magnitude 2 had been recorded as of 11 am on Thursday. The biggest one occurred at 10:17 am on Thursday in Yibin's Gongxian county. It was the fourth aftershock above magnitude 5.

"The frequency is within the normal range. The public don't need to panic," said Du Fang, director of the Sichuan Provincial Earthquake Forecast Research Center.

The June 17 earthquake, which claimed 13 lives, is the biggest ever recorded in Yibin.

Du said the possibility of another major earthquake in the region is small as there is no active big seismological fault within a 50-kilometer radius of the stricken area.

He said the earthquake and its aftershocks, though not high in magnitude, still resulted in some causalities and damage as their epicenters are close to the ground. Poor quality construction of buildings was also a contributing factor.

Yi Guixi, a researcher with the center, said Yibin could continue to be hit by aftershocks for an extended period of time because of seismic interaction among secondary faults.

"Generally, there has been a decline trend in the frequency," he said.

Du Bin, an official in charge of earthquake monitoring and forecasts, said Sichuan province has been accelerating the construction of its seismic intensity rapid reporting and early warning project. The project is expected to start operations this year.