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本文所讨论的南北地震带北段大致范围为甘肃武都到宁夏石咀山和青海民和到陕西宝鸡地区,即北纬33—39度、东经103—107度。从历史上看,本区强震既有与华北强震共起伏的现象,也有与南北带中、南段强震相呼应的事实。然而本世纪六十年代以来,该区没有参与华北和西南地区的强震活动高潮而仅有中等地震活动(图1)。近七年来,全国强震活动和缓,未来成串强震是否会转移到本区有关地区又是一个现实问题。前者涉及到对过去地震予报实践中“虚报”的反省,后者是为了防止另一个极端即“漏报”问题。由于开展前兆观测时间较短(具有连续完整的资料一般不超过十年),靠前兆资料的综合分析解决上述问题为时尚早,现在还不得不求助于地震大形势的分析。
The northern section of the north-south seismic zone discussed in this paper roughly ranges from Wudu in Gansu to Shizui in Ningxia and Minhe in Qinghai to the region of Baoji in Shaanxi Province, which is 33-39 degrees north latitude and 103-107 degrees east longitude. Historically, both the strong and moderate earthquakes in this area have been co-fluctuated with the strong earthquakes in North China, and the fact that they have echoed the strong earthquakes in the middle and south parts of the north-south belt. However, since the 1960s, the area did not participate in the climax of strong earthquakes in North China and Southwest China, but only moderate earthquakes (Figure 1). In the recent seven years, it is a real problem that whether the strong earthquakes in the country will slow down or whether a series of strong earthquakes will be transferred to the relevant areas in the region. The former involves an introspection of “false reporting” in past earthquakes reporting, the latter in order to prevent the other extreme from being “omission”. Due to the short duration of precursory observation (with continuous and complete data generally not exceeding ten years), it is still too early to comprehensively analyze the above-mentioned problems by means of precursor data, and now we have to resort to the analysis of the general situation of the earthquake.