A camera watches to closely track animal behavior. [Photo/IC]

"Our zoo is not transformed into a monitor station because the animals will display abnormal behavior when they are teased by visitors," said Shen.

Possible animal farms need to house more than three species and a pond, if there is one, needs to cover dozens of hectares, so that we have enough samples to do cross checks, said Zhao Bing, division chief with Nanjing seismological bureau.

Preferred farms should be in relatively quiet neighborhoods away from factories or mines.