Scientists puzzled by absence of foreshocks

… and other typical precursors prior to China Earthquake

Published on Global, May 31, 2008.

BEIJING, May 20 (Xinhua) — Some scientists were puzzled by the unusual quiet period of quakes before the 8.0-magnitude earthquake struck southwest China. But others believe there had been precursors, which stood as warnings for a major quake.

“There were no foreshocks and the activity level of minor quakes around the epicenter was low for quite a long time before the earthquake,” said Xiu Jigang, deputy director of the China Seismological Bureau (CSB).

He said there were no short-term anomaly of animals, underground water and other typical precursors, which can lead to a prediction of a major earthquake.

Chinese netizens cited tens of thousands of migrating toads before May 12 in Mianyang, a city close to the epicenter of the earthquake in southwestern Sichuan Province, and unusual cloud formations in east China’s Shandong Province as quake precursors. But experts said they might not be related to the quake.
“There are complicated reasons for the anomaly of animals and underground water. An earthquake is only one of them along with climate change and weather conditions,” said Zhang Guomin, a research fellow with the Research Institute of Seismology under CSB …

… However, research fellow with the Institute of Crustal Dynamics of CSB Qiu Zehua said, China would be able to make substantial progress in short-term prediction if more monitoring stations could be set up in areas which have been found prone to earthquakes.

“I believe that there must be precursors before an earthquake, but they might only happen in areas around the epicenter,” said Qiu. “The problem is that our monitoring stations are too scattered to observe them. We should focus our monitoring efforts in certain targeted areas.”

Researchers in China, a country which suffered 33 percent of the world’s inland earthquakes in the 20th century, are catching up with international seismological studies. In the measurement of the earthquake in Sichuan, the first report by CSB set the magnitude at 7.6 on the Richter scale after the quake on May 12. The quake was shortly upgraded to 7.8, based on more statistics from monitoring stations. Then the bureau revised the magnitude to8.0 on Sunday, with reference to foreign observatories.

The magnitude was revised upward after specialists carried out “real-time and detailed measurements of the quake according to international practices,” said Luo Zhuoli, an expert with CSB.

The quake, claiming 34,073 lives as of 4:30 p.m. Monday and leaving 245,108 injured so far, has caused serious damage to buildings, bridges and other public facilities in an area of more than 100,000 square kilometers.

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