芦山地震的预测

On the Forecasts of the Lushan Earthquake in 2013

2013年4月20日中国四川省雅安市芦山县发生了7.0级地震,对于这次地震发生的时间和地点,震前有不同程度的预测。为了推动地球科学发展,提高地震预测水平,以达到最大限度地减轻地震灾害损失,特对此作一小结。2011年3月11日日本东北部海域发生9级地震以后,利用可公度性原理,分析了近年来发生在世界各地的大地震,发现这些地震发生的时间具有可公度性,且它们基本上发生在其时间轴上的可公度值点上。根据对川滇块体地震信息的可公度性分析,该研究区的可公度值是2.44年,因而2013.24年就是未来地震可能发生的时间点;根据卫星重力异常反映的地壳密度异常变化图,雅安西侧与汶川具有两个特征相同的独立的卫星重力局部高异常梯度突变区,2008年的汶川地震只是释放了龙门山断裂带东北段的能量和应力,这导致能量和应力在龙门山断裂带南西段,特别是南西端与重力异常突变位置的叠加区加速积聚和集中,因此曾佐勋多次指出四川的下一个大震将在雅安与康定之间发生。这两方面的分析都是震前的,可惜它们是彼此独立的。如果事前能将这两个方面的预测加以综合分析,则可以达到短期预测的目的。这再一次表明,地震预测必须走综合分析之路。

A magnitude 7.0 earthquake occurred at the Lushan County, Ya’an City, Sichuan Province, China in April 20, 2013.We had various forecasts of the time and location of this earthquake.In order to advance development of geosciences and improve accuracies of forecasts of earthquakes, which, should help to minimize damages from earthquakes, we summarize these forecasts in this paper.After a magnitude 9 earthquake occurred off the northeastern coast of Japan on March 11, 2011, we used the method of commensurability to analyze the earthquakes in recent years in the world and found that the dates of these earthquakes are all at commensurable points.According to our analyses dates （ in units of years from the A.D.） of earthquakes in the Sichuan-Yunnan block follow a law of commensurability as 2.44K＋b with K an integer numbering between 0 and 5.From this law we predicted an earthquake to occur at the time 2013.24 A.D.in the block, which is consistent with the Ya’an （ Lushan） earthquake.We further checked a map of gravity anomalies from satellite measurements, which actually reflects the distribution of crust-density anomalies.From the map we found that there were two highly abnormal regions of local abrupt changes of gravity gradients on the west side of the Ya’ an and at the Wenchuan County, respectively.The two regions have common characteristics.The 2008 Wenchuan earthquake only released the energy and stress in the northeastern section of the Longmenshan fault zone .In the southwestern section of the fault zone, particularly in the regions of gravity anomalies there, the energy and stress became more concentrated due to the Wenchuan earthquake.Prior to the Ya’an earthquake one of us （Zeng Zuoxun） had noticed the pattern of gravity anomalies and repeatedly pointed out that the next high-magnitude earthquake in the Sichuan Basin after the Wenchuan earthquake was about to happen between Ya ’ an and Kangding.It is unfortunate that the studies of commensurability and gravity anomalies were carried out by different authors without communications about the studies.If the two studies were combined before the Ya’an earthquake, a short-term forecast of the earthquake could have been realized.This once again shows that earthquake forecasts need to take synthetic approaches.