BEIJING, May 13 (Xinhua) — Earthquake forecasting remains a “hard nut” to crack, a Chinese expert told reporters here on Tuesday.
Zhang Xiaodong, vice director and a researcher of the China Earthquake Networks Center, said that 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 on Monday that killed at least 11,921 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 expert made the remarks in response to a reporter’s question about the implications of natural phenomena supposedly reported to employees in the Sichuan seismological bureau by relatives, days before the Wenchuan quake.
Tuesday’s China Daily reported that at least two swarms of toads were seen on the streets of cities in the region days before the quake. The newspaper also reported that a government seismologist, Chen Xuezhong of the China Seismological Bureau, had warned more than five years ago that, based on seismological records and animal studies, a strong earthquake was likely in Sichuan.
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. “We haven’t passed the test of earthquake forecasting.”