Experts said that aftershocks from the magnitude-7 quake in Sichuan province may not cause more substantial damage and injuries, unlike those after the 2008 disaster.

The strength of Saturday's quake, whose epicenter was in Lushan county, Ya'an, was 33 times less than the magnitude-8 quake Wenchuan county five years ago, said Jiang Haikun, deputy director of the China Earthquake Network Center forecasting department.

The more energy released in the seismic activity, the more damage it causes, Jiang said.

There will be many aftershocks from Saturday's quake in the coming days, and some stronger than magnitude 5.0 cannot be ruled out in disaster areas, he said. They can last for months, or even years. But judging from the experience of the Wenchuan quake, he added, the frequency of the aftershocks will diminish.

So far, the strongest aftershock measured magnitude 5.3, at 11:34 am on Saturday, according to the center.

Sun Shihong, a retired chief forecaster at the China Earthquake Administration, agreed with Jiang, saying the damage from Saturday's quake will not be as extensive as that in 2008.

"When the massive earthquake hit Wenchuan five years ago, Ya'an was one of the serious disaster areas. Consequently, the houses and buildings there were reinforced, and that is a good thing that came from the disaster," he said.

Damage to the earthquake-resistant buildings will not be severe, and there may be fewer injuries from houses collapsing than in 2008, he said.

"There is indeed some relationship between the two big quakes, because Saturday's was about 200 kilometers away from the earlier one and it formed in the same way as the 2008 quake," he said. Both occurred along the Longmen Mountain Fault, he said.

But Saturday's quake was not an aftershock of the Wenchuan quake, he said.

Chen Xuezhong, head of the administration's Institute of Geophysics, agreed, saying the seismic events occurred in different parts of the fault zone.

"The earthquake in Ya'an was a new shock along the fault line, but in a different direction. It was the southern part on Saturday, and in 2008 it was the northern," he said.

But Chen Yuntai, a geophysicist at Peking University, concluded that the Ya'an quake was the biggest aftershock of the Wenchuan quake after considering its location, energy released and fault direction.

After the magnitude-8 Wenchuan quake, many of the aftershocks measured around magnitude 6.0, and the largest was magnitude 6.4 on May 25, 2008, Chen said.

"Generally, the biggest aftershock is about magnitude 1.2 smaller than the earthquake itself. Thus, Saturday's quake can be regarded as the biggest aftershock (of the Wenchuan quake)," he said.

By Saturday evening, more details of the Ya'an quake were being examined, the center said.

"We'll keep watching for aftershocks and avoid more secondary damage or disasters hitting this place again," Sun said.

Southwestern China has been the scene of several deadly earthquakes. The area is on the boundary between the Indian and Asian tectonic plates, which grind against each other.

Worldwide, there have been 12 earthquakes stronger than magnitude 7 this year, and such massive seismic events occur on average 18 times annually, according to the center.

caoyin@chinadaily.com.cn

(China Daily 04/21/2013 page2)