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本文对川滇地区自有地方台,网建立以来的21年间记录到的239次小震群进行了研究,发现Ms≥6.7级的强震绝大多数都发生在小震群年频度增高的背景上。并引用了归一化熵值K作为衡量震群序列中能量分布均匀度的特征量,分析了不同K值的震群与中强震发生的对应关系,发现K≥0.8的震群发生与Ms≥5.5的中强震发生的对应率为59.3%;虚报率为40.7%;漏报率约占14%。K<0.8的震群发生满足无震条件的约占56%。以上结果表明,用归一化熵值K≥0.8来区别前兆震群与一般震群,结果没有华北地区的那样显著。在川滇地区,要将所对应的强震震级提高到6.5级,结果才比较好。
In this paper, 239 small earthquakes recorded in the past 21 years since the establishment of local stations in Taiwan and Sichuan have been studied. It is found that most of the strong earthquakes of Ms≥6.7 occur in the high frequency of small earthquakes On the background. The normalized entropy value K is used as the feature quantity to measure the energy distribution uniformity in the earthquake swarm sequence. The correspondence between the earthquake swarm with different K values and the occurrence of moderate strong earthquakes is analyzed. It is found that the swarm with K≥0.8 and Ms The corresponding rate of moderate-strong earthquakes ≥5.5 was 59.3%, the false alarm rate was 40.7% and the false negative rate was about 14%. Seismic occurrences with K <0.8 satisfy about 56% of the conditions without earthquake. The above results show that using the normalized entropy value K≥0.8 to distinguish the precursory swarm and the general swarm, the result is not as significant as in North China. In Sichuan and Yunnan, it is better to increase the magnitude of the corresponding strong earthquake to 6.5.