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三种不同类型的地震预测
Long-term prediction 长期预测 As Christopher Scholze described : Christofpher Scholze做了如下描述3∶ “Long-term prediction, which is the estimate, on a decadal time scale, of the probable failure time of segments of active faults, is now an established part of seismic hazard analysis9 . On the basis of that methodology, several studies forecast the 1989 Loma Prieta, California, earthquake in the six years before that event10 . The utility of this kind of prediction is that with a decadal lead time, it can guide engineering and emergency planning measures to mitigate the impact of the earthquake. An intermediate-term prediction is an update of the long-term prediction brought about by an increase in seismicity (Fig. 1D) or some other indicator that the fault is near its failure point.” “长期预测，是对于活跃性断裂带某一段可能破裂的时间的一种十年标度的预计，目前作为地震风险分析的组成部分之一4。在该种方法基础上，数项研究在地震发生前六年对1989年加利福尼亚州Loma Prieta地震进行了预测5。该种类型预测的应用，是利用其十年数千范围的提前量，对工程设计和紧急计划措施予以指导，以便减轻地震的造成的冲击。中期预测则是地震活动性增加〔图1D〕，或表明断裂带接近于破裂点的某种其它指标，而对长期预测进行的更新。 David Bowman & Charles Sammis also pointed out : David Bowman & Charles Sammis也指出6∶ “But what about forecasting earthquakes on the year-to-decade scale? Although 'predictions' over this timescale might not justify such drastic actions as the evacuation of cities, it would certainly give policy-makers as well as individual citizens sufficient time to brace themselves for the impending event, in much the same way that California was able to prepare itself for last winter's El Niño. With this paradigm in mind, forecasting on the year-to-decade scale would be immensely useful.” “但是，对地震进行一年至十年数值范围的预测如何？尽管依照这样的时间标度进行的‘预测’，不能作为撤退城市居民这样的激烈行动的决策依据，它肯定将给决策者们，以及居民个人，足够的时间振作精神对迫近的地震事件做好准备，就象加利福尼亚州对去年冬季对厄尔尼诺气候做好准备一样。考虑到这个范例，对地震进行一年至十年标度的预测将非常有用。” Against even such possible merits of “Long-term forecasts”, Robert J. Geller stated : 连“长期预测”的益处都反对，Robert J. Geller声称7∶ “Long-term forecasts: where do we stand?” “长期预测”∶我们处于何种地位？ “If they were reliable and accurate, long-term forecasts could be useful in engineering and emergency planning measures to mitigate the impact of earthquakes. Unfortunately, however, there is serious question about the accuracy and reliability of proposed methods for long-term seismicity forecasts.” “如果可靠的和准确，长期预测对于采取工程和紧急救援规划方面措施，减轻地震造成的冲击方面可能有用。然而，遗憾的是，对于长期地震活动性预测所提议的方法的准确性和可靠性方面存在着严重的问题。” “The downside of long-term forecasts” “长期预测的不利之处” “Until we have well validated methods, we should be reluctant to recommend that government authorities take strong action on the basis of long-term forecasts, although no great harm and some good is likely to result from taking sensible precautionary measures on a moderate scale in regions for which long-term forecasts have been issued.” “在我们有经良好验证过的方法之前，我们应当在推荐政府当局在长期预测基础上采取有力度的行动方面应当谨慎。然而，对于那些已发布长期预测的地区，采取明智的适度预防性措施，看来能够获得某些好处和不会造成很大损害的结果。” “There is, however, a risk that the authorities in regions for which long-term forecasts have not been issued may become overly complacent. This is not merely a theoretical possibility. Several hypothetical future earthquakes in and around the Tokyo area have been the subject of extensive discussion in Japan for the past 25 years (see section 5 of ref. 1 ). Partly as a result of these forecasts, local governments in western Japan, including Kobe, incorrectly assumed that their region was not at significant risk, and failed to take sufficient precautionary measures against earthquakes. This was one of the causes of the unexpectedly large damage caused by the 1995 Kobe earthquake.” “然而，对于没有发布长期预测的地区政府可能导致当局过于洋洋得意的风险。这不仅仅是一种理论性的可能性。关于东京及其邻近区域可能发生几次假定的未来地震，一直是日本过去25年期间认真讨论的议题〔参看参考文献8的第5节〕。部分由于这些预测的结果，日本西部地方政府，包括神户，错误的预计它们的区域不面临这方面重大的风险，从而未能对地震采取足够的预防性措施。这是1995年神户地震造成没有预计到的重大损失的原因之一。” Immediate Alert 即震报警 Also as Christopher Scholze described3: Christopher Scholze描述如下3∶ “In another type of prediction, an Immediate Alert, seismic waves above a certain threshold send an electronic alert, which, with a lead time of several seconds, can be used for such things as shutting down nuclear reactors, gas and electricity grids, and the like. A system like this is in use in Japan to stop high-speed trains in the event of an earthquake.” “在另一种类型的预测中，即即震报警，超过一定限度的震波将发出电子报警，比发震时间有几秒钟的提前量，可以用于关闭核电站反应堆、燃气和电力网等。这样一种系统在日本用于在发生地震时终止高速列车的运行。” Short-term earthquake prediction 短期地震预测 One of the sharpest contradictory arguments of the debate is on this topic. 这个议题上的争论是这场辩论中最尖锐的争论之一。 In the opening session, Ian Main stated : 在开场白中，Ian Main宣称9∶ “Earthquake forecasting. Here we would try to predict some of the features of an impending earthquake, usually on the basis of the observation of a precursory signal. The prediction would still be probabilistic, in the sense that the precise magnitude, time and location might not be given precisely or reliably, but that there is some physical connection above the level of chance between the observation of a precursor and the subsequent event.” “地震预测。这里，通常在观察前兆信号的基础上，我们试图对迫近的地震的某些特点进行预测。该种预测仍然是概率性的，即准确的震级、时间和位置未能准确或可靠的给出。但是，在观察到的前兆和而后发生的地震之间有超过偶然机会的某些物理联系。”
Christopher Scholze stated3: Christofpher Scholz宣称3∶ “What, then, should we do about short-term earthquake prediction? Should we declare it impossible and banish it from our minds? I think not: there is much yet to be learned about earthquake physics, and rapid progress is being made, particularly in the applications of the rate/state variable-friction laws to the problem12 . Until now we have been working in the dark, with the only observables being the earthquakes themselves.” “那么，我们应当对短期地震预测怎么办？我们是否应当宣布它是不可能的，并将它从我们的思维中排除掉？我想不应当∶在地震物理学方面还有那么多需要了解，快速的进展也正在实现，特别在对地震问题应用速率／状态变量—摩擦规律方面10。直到现在我们一直在黑暗中工作，唯一的观察对象仅是地震本身。” Dense permanent global positioning system (GPS) networks are presently being installed in California and Japan and elsewhere that, together with satellite radar interferometry, will allow us to view for the first time the evolution of strain fields in space and time. However, Robert J. Geller took a seem to be extreme but actually rather practical position : 然而，Robert J. Geller采取了一种看来极端事实上相当实际的立场11∶ “The public, media, and government regard an 'earthquake prediction' as an alarm of an imminent large earthquake, with enough accuracy and reliability to take measures such as the evacuation of cities. 'Prediction' is used exclusively in the above sense here; in other words, longer-term forecasts of seismic hazards or statistical forecasts of aftershock probabilities are not classified as predictions.” “公众、新闻媒介，以及政府视‘地震预测’为对即将来临的大地震的报警，其准确性和可靠性足以采取从城市中疏散居民这种措施。‘预测’在此的含义仅限于此；换句话讲，对地震风险的长期预测，或对余震可能性的统计性预测，均不能分类为预测。” On such a view, referred as “deterministic prediction”, in his Introduction to this debate, Ian Main described it as follows: 对于这样的看法，即称之为“确定性预测”的含义，在本次辩论的引言中，Ian Main对其描述如下∶ “Deterministic prediction. Earthquakes are inherently predictable. We can reliably know in advance their location (latitude, longitude and depth), magnitude, and time of occurrence, all within narrow limits (again above the level of chance), so that a planned evacuation can take place. ... Time-independent hazard has now been standard practice for three decades, although new information from geological and satellite data is increasingly being used as a constraint. In contrast, few seismologists would argue that deterministic prediction as defined above is a reasonable goal in the medium term, if not for ever12 .” “‘确定性预测’。认为地震具有内在的可预测性。我们可以事先可靠地知道它们的位置〔经度、纬度和深度〕，震经，以及发震时间，均在狭窄的误差限度之内〔重申在偶然机会水平之上〕，使得可以实施计划中的疏散……‘时间上独立的风险评估’三十年来一直作为一种标准的实践，尽管越来越多采用地质方面的和卫星探测的数据作为一种约束。与此相反，很少地震学家会争论上述内容定义的‘确定性预测’是一项合理的中期目标，或永远不是合理的目标12。 David D. Jackson pointed out : David D. Jackson指出13∶ “For real progress we need a methodical approach and a better strategy for testing hypotheses. We have good reason to expect wonderful discoveries, but not deterministic prediction.” “对于真正的进展来讲，我们需要对假说进行试验的一种系统的途经和更好的战略。我们有很好的理由来期望令人惊讶的发现，但不能期望‘确定性预测’。”
Max Wyss’s views seem to be reflecting a more common outlook: Max Wyss的看法看来反映一种更普遍的看法∶ “The future of earthquake prediction research ... I am pessimistic about the near future and optimistic about the long term. ... However, there can be no doubt that a preparatory process to earthquake rupture exists (foreshocks demonstrate this), and I am confident that ingenious and resilient people, who will come after us and will be amused by this tempest in a teapot about the prediction of earthquakes, will eventually improve our ability to predict some earthquakes in favourable areas, although not often with time windows as short as demanded by the moderator.” “对于地震预测研究未来的前景……我对其短期前景较为悲观，但对于其长期前景比较乐观……然而，地震破裂发生前存在着一个孕育准备阶段应毫无疑义〔前震显示了这一点〕，我也相信有独创性和韧性的人会跟随我们，并将会对地震预测的令人激动性所吸引，这终将改进我们在条件有利的区域对某些地震实现预测的能力，尽管预测时的时间偏差不一定能够短到这场辩论主持者所要求的程度。” 接续后篇∶
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陈一文 （cheniwan@263.net） 上传2007.01
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