【摘要】 作为活化的古老克拉通,华北地区的地震活动非常频繁。上世纪60年代以来,华北地区曾经发生了1966年邢台M7.2,1975年海城M7.3和1976年唐山M7.8等地震。2012年5月28日,在唐山地震震源区又发生了M4.8地震,引起了国内外地学界的广泛关注和争议。争议的焦点在于此次地震是1976年唐山地震的余震,还是唐山地区乃至整个华北地区新一轮地震活动开始的预兆。本文利用华北地区过去40多年的地震活动资料,研究了邢台、海城和唐山地区的地震活动。研究结果显示,邢台、海城和唐山地区过去30多年的小震活动明显高于这些地区大震前的地震活动及华北地区的背景地震活动,应是余震。同时由GPS资料计算的邢台、海城和唐山地区的地壳水平应变率也明显高于华北地区的背景值。这些小震活动和地壳水平应变率同时表明邢台、海城和唐山强震区的余震数十年后仍在持续。震后粘性松弛可能是华北地区长时间余震持续的主要原因。更多还原

【Abstract】 As a Mesozoic decratonization craton,seismicity is intense in North China.Since the 1960s,several major earthquakes occurred in North China,including the 1966 Xingtai M7.2 earthquake,the 1975 Haicheng M7.3 earthquake,and the 1976 Tangshan M7.8 earthquake etc.Recently,a small earthquake sequence occurred in the hypocenter region of the 1976 Tangshan M7.8 earthquake.The sequence has caused widespread concerns and heated debate.In the science community,the debate is whether the recent Tangshan earthquakes are the aftershocks of the 1976 earthquake or are harbingers of a new period of active seismicity in the area and the rest of North China,where seismic activity seems to fluctuate between highs and lows over periods of a few decades.Seismic activity in the Xingtai,Haicheng and Tangshan regions is studies based on the small earthquake catalog in the past 40 years.The results show that seismic activities in the three regions are more frequent than not only regional seismicity before major earthquakes,but also the background seismicity in North China.Despite the earthquake activity,present-day crustal strain rates in the Xingtai,Haicheng and Tangshan regions obtained from GPS survey are also obviously higher than the background strain rates in North China.Both the small earthquake activity and the crustal strain rate indicate that the recent seismicity in the Xingtai,Haicheng and Tangshan regions should be aftershock sequences of last major events in the regions,respectively.The aftershock activity should last at least tens of years in North China.The crustal stress relaxation after major earthquake may be one of the major reasons for the long aftershock sequence in North China.更多还原