2004年9月17日阳江4.9级地震序列的一些特征
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摘要
2004年9月17日阳江M4.9级地震是1969年阳江M6.4级地震发生后至今震级最大的余震之一,该震中区及附近1970年以来至2004年底的九千余次ML1级以上的地震月频次的统计结果显示,本地4.5级以上地震震前短临时段内,ML 1.0级以上小震活动水平增强不明显,但2004年与1986年的地震临震前,ML0.1级以上的微震次数却异常升高;本地4.5级以上地震前3个月至1年左右,b值均处于0.55左右的低值状态。衰减系数H值的计算均大于1,显示本地4.5级以上地震的余震衰减都很快,在较短时间内呈现出孤立型较强的特点。本次4.9级地震作出的震源机制解显示为走滑型,与1969年主震的情况较为类似。
After the M6.4 earthquake occurred in 1969,Yangjiang M4.9 earthquake in 2004 is one of the biggest aftershocks among the 9429 aftershocks(ML≥1.0) in the area.The frequency curve shows the seismic activity level didn′t rise obviously before the M≥4.5 earthquake in a short and imminent time span.But the frequency curves of the microquakes in 1986 and 2004 main shock rise obviously.Before the M≥4.5 earthquakes the b value curve decreased to about 0.55.The decay coefficient H of the M≥4.5 earthquakes shows that the frequency of the aftershocks decayed rapidly and that series should belong to the isolated type series in a short time.The focal mechanism of the M4.9 earthquake shows that it belongs to strike slip type that is similar to the M6.4 earthquake in 1969.
After the M6.4 earthquake occurred in 1969,Yangjiang M4.9 earthquake in 2004 is one of the biggest aftershocks among the 9429 aftershocks(ML≥1.0) in the area.The frequency curve shows the seismic activity level didn′t rise obviously before the M≥4.5 earthquake in a short and imminent time span.But the frequency curves of the microquakes in 1986 and 2004 main shock rise obviously.Before the M≥4.5 earthquakes the b value curve decreased to about 0.55.The decay coefficient H of the M≥4.5 earthquakes shows that the frequency of the aftershocks decayed rapidly and that series should belong to the isolated type series in a short time.The focal mechanism of the M4.9 earthquake shows that it belongs to strike slip type that is similar to the M6.4 earthquake in 1969.
引文
①广东省地震局地震应急指挥部办公室.2004年9月17日阳江市平冈镇4.9级地震应急工作总结,2004.
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