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由于对美国东部地震的产生机理还不清楚,所以,还不可能预测这一地区的地震何时何地发生。一种预测本区未来大地震地点的方法,就是用来编制国家地震危险地图集的最新版本所用的部分方法。这种方法主要是利用较小地震(M≥3)的空间分布预测较大地震(M≥5)的地点。运用这种方法的基本假设是,较小地震所勾划出的地点是能够发生较大地震的。我们很想知道,这一方法对于一次按比例缩小的模拟,其使用的效果如何。在模拟中,用美国东北部及邻近地区地震台网所记录的甚至更小的地震(M≥2)的空间分布,来“预测”已经发生的较大地震(M≥4)的地点。我们用这种按比例缩小震级的方法来研究用小地震空间分布预测板块内部较大地震发生地点的可能范围。工作的实质是系统地分析在大地震附近先发生小地震的频度。我们设计了3种统计和报告方法,来研究小地震是否倾向于发生在未来大地震的震中地区。研究发现,平均看来,大地震在小地震附近发生的频度大于大地震随机分布的频度。但是,有很多大地震并不是根据小地震的分布来做出预测的。这意味着,如果我们要采用这种方法,就目前预测大震地点的水平而言,就不得不满足于有一定数量的“错过”。或许,这种对大地震地点的预测能力水平,是在给定的对本地区地震成因机制认识现状的条件下,我们所能预期取得成功的水平的现实估计。
It is impossible to predict when and where earthquakes in the region will occur because of the mechanism of the onset of the eastern United States earthquake. One way to predict the location of future major earthquakes in this area is to use some of the methods used to compile the latest version of the National Seismic Hazard Atlas. This method mainly uses the spatial distribution of smaller earthquakes (M≥3) to predict the location of larger earthquakes (M≥5). The basic assumption in using this method is that larger earthquakes can occur at the site delineated by smaller earthquakes. We would love to know how effective this method is for a scale-down simulation. In the simulations, the spatial distribution of even smaller earthquakes (M ≥ 2) recorded by seismograph networks in the northeastern United States and adjacent regions was used to “predict” the locations of the larger earthquakes (M ≥ 4) that have occurred. We use this method of down-scaling to study the possible range of predicting locations of major earthquakes within a plate using the spatial distribution of small earthquakes. The essence of the work is to systematically analyze the frequency of small earthquakes that occur first in the vicinity of a major earthquake. We have devised three statistical and reporting methods to study whether small earthquakes tend to occur in the epicenter of future major earthquakes. The study found that, on average, large earthquakes happen more frequently than small earthquakes occur more frequently than large earthquakes. However, many large earthquakes do not make predictions based on the distribution of small earthquakes. This means that if we were to adopt this method, we would have to be content with a certain amount of “missing” in terms of the current prediction of the locations of major earthquakes. Perhaps this level of predictive ability for sites of major earthquakes is a realistic estimate of the level of success we can expect given given the current state of knowledge about the genetic mechanism of the earthquakes in the region.