鄂尔多斯周缘地震带地震活动的分期和相关分析

PERIOD DIVIDING AND CORRELATION ANALYSIS OF SEISMICITY IN THE SEISMIC ZONES AROUND THE ERDOS BLOCK

利用最优分割法对鄂尔多斯周缘地震带(区)的地震活动进行了分期,并作了相关分析。结果表明,1000年以来汾渭地震带北段可划为4个活跃期,每个活跃期的中心间距约300年,最大地震为7级,天水—陕南地震带(区)近一、二百年的地震活动可分为持续约10年左右的几个地震簇。所有分期中,海原地震带能量释放最大,且最近仍很活跃。汾渭地震带和海原—银川地震带活跃期存在相关现象,且其南段往往先于北段活跃,目前活动水平较低。该带1900年以来地震还有与河套地震带地震相呼应的现象和沿构造带南北迁移的规律。根据分期和相关结果推测,鄂尔多斯周缘各地震带都存在中强地震背景。其中海原—银川地震带近期发生5—6级或更大地震的可能性较大,天水—陕南地震带近期也有发生中强地震的可能。汾渭地震带虽然存在孕育6级以上大震的背景,但近年还不会发生强震。

Period dividing of seismicity by the optimal section and correlation analysis of scismicity of the seismic zones around the Erdos Mock arc respectively made in this paper. The result shows that the north segment of Fenwei seismic zone can be divided into 4 active periods since 1000, with the centers of those periods being approximately 300 years apart. The maximum earthquake was an event of about M7. Seismicity of Tianshui-south Shaanxi seismic zone can be classified into several clusters, each of which lasted about 10 years in the recent 1 or 2 centurier. Haiyuan seismic zone had the largest seismic energy release in all the periods, and is presently still rather active. The seismicity of Fenwei seismic zone correlates with the period during which Haiyuan-Yingechuan seismic zone was active, and is presently showing a lower level of activity. Earthquakes occurred since 1900 along the south segment of Fenwei seismic zone correlate with those along Hetao seismic zone, and the scismicity seems to migrate south or northward along the Fenwei graben. It is inferred that there exists a background lor moderately-strong and strong earthquake occurrences in the future in all the zones, among which the Haiyuan-Yingchuan seismic zone is more vulnerable in recent times, whereas south Shaanxi seismic zone might also be hit by a moderately-strong or strong event. Fenwei seismic zone might not be hit by strong earthquakes in the next one year or two although it possesses the background tor generating a strong earthquake.