Meeting the Challenge of Imminent Earthquake Prediction
By Wei Xinde, staff reporter of Chinese Science News, May 9, 1997
A number of large earthquakes have occurred this year in the Jiashi area of Xinjiang province, China. They have caused great concern among experts and the general public at home and abroad. While many of the earthquakes that occurred in April were over magnitude 6.0, only nine people died among the affected population of more than 300,000.
Imminent Earthquake Prediction Made A Great Contribution
As early as March 7, the Chinese State Seismological Bureau (SSB) brought together experts from their Center for Analysis and Prediction (CAP) and other SSB units in Beijing to assess the earthquake situation in Jiashi. They agreed that they should "… pay attention to the possibility of another earthquake of magnitudes between 5 and 6, or even as high as 6, in the Jiashi area."
Later, on March 13 and 20, based on the anomalies associate with the series of Jiashi earthquakes, and the shifting of local geomagnetic minimum in the region, CAP issued this statement: "..there may be another earthquake between magnitude 5 and 6 and even as high as 6 in the Jiashi area, especially during the period from March 20 to April 13."
On March 26, Xinjiang Seismological Bureau also submitted a short-term and imminent earthquake prediction report to the SSB, stating that “...between April 1 and July 1, there is a high probability of a magnitude 6 earthquake in the Wuqia and Jiashi area."
On April 3, Huang Xiangning (Associate Research Fellow of the Institute of Crustal Stress of the SSB), Prof. Li Junzhi (Earthquake Research Center, Beijing Polytechnic Institute), and Ren Zhenqiu (Chinese Academy of Meteorological Science) jointly presented a short-term and imminent earthquake prediction report to the SSB. Their conclusion was that there would be an earthquake of magnitude 7 to 7.5 at 38.7N-40.2N, 75E-77E on April 7 (+/-3 days).
On April 3, the SSB Prediction Section and the Center of Analysis and Prediction forwarded the prediction reports to the Xinjiang Seismological Bureau.
At 7 p.m. on April 5, the Xinjiang Seismological Bureau convened an emergency meeting to discuss the imminent earthquake prediction reports and decide on a course of action. At 8 p.m. the Bureau recommended that the Jiashi County Government take immediate action and mobilize the general public to take earthquake protection measures. These precautionary measures greatly reduced human casualties and economic losses.
[ On April 6, 7:46 a.m. Beijing time, a magnitude 6.3 earthquake occurred; at 12:36 p.m. another quake of magnitude 6.4 hit the Jiashi County. Although more than 2000 houses collapsed, there was no loss of life and only 23 people were slightly injured.* ]
Profs. Li Junzhi, Ren Zhenqiu, and Huang Xiangning received a personal telephone call from the head of CAP after the earthquakes congratulating them on their "..pivotal role in this (successful) warning." The three experts, however, continued to warn that "there is still a high probability of an even greater earthquake because the seismic energy in the Jiashi area has not been fully released." Sure enough, on April 11 and 16, two more quakes (M6.6 and M6.4) followed. The total energy eventually released in this series of M>6 Jiashi quakes between April 6 and 16 was equivalent to a single M6.8 earthquake, close to the M7 earthquake predicted by the three experts. This particular prediction by the three experts is considered accurate on all three parameters: time, location and magnitude, a distinguished achievement in China and abroad. The Chinese scientists have begun to make some breakthroughs in the global problem of short-term and imminent quake prediction.
Many Years of Chinese Scientific Efforts Pays Off
This successful prediction was hardly accidental. Over a hundred earthquakes occur daily around the world. But many of them are small in magnitude and escape human detection. People, however, are concerned about devastating earthquakes, and they welcome scientists to make accurate short-term (within months) or imminent predictions (within days or hours) before a major earthquake.
An earthquake prediction must consist of three basic parameters: time, location, and magnitude. To-date, even the most accurate earthquake prediction method can only achieve a success rate of 30%. Therefore many scientists in the world do not yet consider earthquakes predictable. However, Mr. He Yongnian, Deputy Director of SSB, stated recently that Chinese scientists are optimistic regarding earthquake prediction.
In particular, Chinese scientists have made ten successful predictions of destructive earthquakes (M>6) since the devastating Great Tangshan Earthquake in 1976. A huge amount of earthquake data have been accumulated to form the scientific basis for recognizing earthquake patterns and evaluating predictions. These achievements are unique to the Chinese scientific community.
In China, a corp of dedicated 'volunteer' scientists in a variety of disciplines work alongside professional earthquake scientists at the forefront of earthquake prediction. Out of a sense of civic duty, these volunteer scientists have made unremitting efforts in monitoring and predicting earthquakes over the years, despite the lack of research funding. Realizing that East Asia is entering into the fifth period of peak seismic activity for this century, China's State Science and Technology Commission and the United Nations Department of Development Support and Management Services (UNDDSMS) established the Global Programme for the Integration of Public Administration and Science of Disasters. The Global Programme has a coordination unit based in the Institute of Geology, Chinese Academy of Sciences, and facilitates the collaboration of many of these volunteer and professional earthquake scientists.
The Global Programme has brought Profs. Li, Ren, and Huang together in their earthquake prediction efforts. In the past two years, the team has presented five short-term and imminent earthquake predictions to the SSB. Two were essentially correct in all three parameters, while two predictions for earthquake beyond China's border (but issued to SSB only), were essentially correct in two out of the three parameters. In 1996, they predicted a M6.5 earthquake in the Hetao area (40.5N-42N, 108E-110E) between March 18 and March 25. A quake of M6.4 occurred in Baotou (in the Hetao area) on May 3. The location and magnitude they had predicted were correct, while the time was off by 39 days. It is worth noting the short-term and imminent prediction made in May 1995. Although one element was incorrectly predicted, Arthur Holcombe, Resident Representative of UNDP, conveyed to Song Jian, Minister of the State Science and Technology Commission, three days after the earthquake, the Japanese government's appreciation for the Chinese prediction, which their scientists did not make using customary approaches.
Mr. Holcombe also mentioned that the techniques Chinese scientists employ differ from ones used in other countries. While scientists around the world mainly employ seismology, Chinese scientists utilize geoelectricity, geomagnetism, planetary science, meteorology, hydrology, crustal stress, infrasound, and abnormal animal behavior.
Integrated View of Internal and External Causes of Earthquakes
Profs. Li, Ren, and Huang summarize their methodology as one that integrates internal and external causes. Although there are now as many as over a hundred methods in earthquake prediction, none of them, in the minds of practically all quake experts, is reliable by itself. In their Jiashi quake prediction report card, the team gave the following supporting facts:
By integrating their individual studies of internal and external causes of earthquakes and their long-term observations, the team looks for coincidental occurrences of causes. The successful prediction methods they have come to rely on over the years are:
1) Infrasonic Method
Infrasonic waves have specific decay characteristic while propagating through a solid medium (such as the Earth's crust). Professor Li discovered that within 9 days before a major earthquake, abnormal infrasonic waves can be detected. Used in imminent prediction, this method has an error in time of less than 4 days and error in magnitude of less than M0.8. He has not yet been able to demonstrate prediction of location.
2) Crustal Stress Method
Prominent Chinese geologist Dr. Li Siguang [known in the West as Dr. J.S. Lee] once remarked that the birth of an earthquake is a mechanical process. Prof. Huang Xiangning discovered that the longer the time of abnormality in crustal stress, the stronger the impending earthquake. His empirical formula has been able to predict the magnitude within an error of +/-M0.5. Moreover, he discovered that the intersecting area of the principal crustal stress directions as measured at different monitoring stations can locate the epicenter of impending earthquakes.
3) Resonant Superposition of Tide-Generating Forces
Ren Zhenqiu discovered that calculating resonant superposition of tide-generating forces is a good tool for earthquake prediction. Long-term observations show that this method, coupled with an understanding of seismic mechanisms, can predict earthquake occurrence time to within 3 to 5 days, and the location to within 150 to 220 km.
Among the three prediction methods, infrasonic wave and crustal stress may be considered "internal" instability conditions found in the pre-seismic process. Tidal force resonance may be considered an external factor that can trigger an earthquake when the internal instabilities exist.
Other emerging techniques for earthquake prediction include geological micro-vibration, satellite [infrared] imaging and abnormal Earth signals. Reflecting the holistic Chinese approach, the three experts agree that the different prediction methods should be considered in concert as much as possible. They would only issue an imminent prediction when all three of their methods point towards an impending event. However, they stress that their work is still in its early stages. While some preliminary results are encouraging, imminent prediction is still a complex problem. Given the risk of strong earthquakes in China in the next two years, mitigating measures and vigilance should be stressed. With scientists in all fields stressing multidisciplinary collaboration and accuracy in research, we can be optimistic about a breakthrough in earthquake prediction and earthquake risk reduction in the near future.