Quake forecasting a 'hard nut' to crack: Chinese expert

Uzbekistan News.Net
Tuesday 13th May, 2008 (IANS)

Beijing, May 13 (Xinhua) Forecasting an earthquake remains a 'hard nut' to crack, a Chinese expert told reporters here Tuesday even as a local newspaper reported that a seismologist had warned against a possible strong earthquake in Sichuan region five years ago.

In a press conference, Zhang Xiaodong, vice director and a researcher of the China Earthquake Networks Centre, said the inaccessibility of the Earth's interior, the complex rhythm of earthquakes and the low probability of a quake at any given place was behind the 'thorny' nature of earthquake forecasting.
'We can only gauge underground changes based on observations on the surface of the Earth,' he said.
The press conference was held as rescue work continued in southwestern China, which was struck by a 7.8-magnitude quake Monday that killed more than 12,000 people.
According to Zhang, experts have learned through years of study that seismic rhythms are quite complex, depending on geological structures, time periods and the magnitude of earthquakes.
Earthquakes happened every year somewhere in the world, he said, but for any specific region, the cycle could be thousands of years long.
For researchers, a cycle required samples for calculation. But 'the sample (for quakes) was very hard to obtain even in a lifetime,' he said.
The official, however, said the difficulty of forecasting 'doesn't mean we can do nothing in the area'.
'In the past 20 years, we have detected earthquakes prior to more than 20 incidents. However, the proportion was (of detection among actual quakes) very low,' Zhang said, adding, 'We haven't passed the test of earthquake forecasting'.
The official English newspaper, China Daily, Tuesday reported that seismologist Chen Xuezhong of the China Seismological Bureau had warned more than five years ago, based on seismological records and animal studies, that a strong earthquake was likely in Sichuan.
The newspaper also said that at least two swarms of toads were seen on the streets of cities in the region days before the quake.

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