九江—瑞昌地震序列的波速比特征研究
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摘要
根据多台和达法,利用数字地震观测记录对九江-瑞昌地震序列的波速比特征进行研究,获得了具有参考价值的结果:(1)在震源深度10km上下,波速比平均值存在差异,差异层位正好是江西地区上地壳和中地壳的分界层位,与2005年11月26日九江—瑞昌5.7级地震的震源深度一致,这种现象可能反映了震源位置附近的介质物理性质和化学性质存在变异,可能与这次地震的孕育和发生有着密切联系。(2)在震源区的较小范围内,沿地震序列的北西优势走向,两侧的波速比平均值大小不同,反映出地质结构和岩石性质存在差异,其差异分界线走向与震源机制解中的一组北西向节面走向一致,推测九江—瑞昌5.7级地震可能是由一条北西向断裂活动引起的。(3)2005年12月3日ML3.9级余震前,波速比连续出现超出警戒线的高值异常,回落到平均值以下后地震发生。目前九江—瑞昌地震序列的波速比持续处于高值异常,应当警惕回落到平均值以下后发生显著有感地震。
Through analysis on the characteristics of V_P/V_S ratio in the series of Jiujiang-Ruichang earthquake we found:(a) there is a difference in the mean V_P/V_S ratio 10km beneath the surface,which is just dividing layer of upper crust and middle crust in the area,and it is consistent with the depth of Jiujiang-Ruichang M_S(5.7 earthquake) that occurred on November 26,2005 in the region.It indicated that there were some variations in the physical and chemical character of the medium in the vicinity of hypocenter,which may be closely relevant to the development and occurrence of the earthquake.(b) along northwest of the series' dominant direction in the vicinity of hypocenter,the mean V_P/V_S ratio at both side is different,it indicates there is difference in geological structure and rock character.As the dividing line of difference is consistent with the northwest strike of one group nodal planes in the focal mechanism solution,we guess that Jiujiang-Ruichang M_S5.7 earthquake may be caused by a northwest active fault.(c) Before the M_L3.9 aftershock that occurred on December 3,2005,the V_P/V_S ratio appeared continuously high value anomalies,which went beyond the warning line.After the V_P/V_S ratio recovered below the mean value,the aftershock occurred.At present,the V_P/V_S ratio keeps in high value anomaly,we should be alert the occurrence of felt earthquakes when the mean value drop.
Through analysis on the characteristics of V_P/V_S ratio in the series of Jiujiang-Ruichang earthquake we found:(a) there is a difference in the mean V_P/V_S ratio 10km beneath the surface,which is just dividing layer of upper crust and middle crust in the area,and it is consistent with the depth of Jiujiang-Ruichang M_S(5.7 earthquake) that occurred on November 26,2005 in the region.It indicated that there were some variations in the physical and chemical character of the medium in the vicinity of hypocenter,which may be closely relevant to the development and occurrence of the earthquake.(b) along northwest of the series' dominant direction in the vicinity of hypocenter,the mean V_P/V_S ratio at both side is different,it indicates there is difference in geological structure and rock character.As the dividing line of difference is consistent with the northwest strike of one group nodal planes in the focal mechanism solution,we guess that Jiujiang-Ruichang M_S5.7 earthquake may be caused by a northwest active fault.(c) Before the M_L3.9 aftershock that occurred on December 3,2005,the V_P/V_S ratio appeared continuously high value anomalies,which went beyond the warning line.After the V_P/V_S ratio recovered below the mean value,the aftershock occurred.At present,the V_P/V_S ratio keeps in high value anomaly,we should be alert the occurrence of felt earthquakes when the mean value drop.
引文
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[3]刘继录,张从珍,曹肃朝,等.张北6.2级地震前后波速比在源区与场区的变化特征[J].华北地震科学,2001,19(2):14-20.
[4]梅世蓉,冯益德,张国民,等.中国地震预报概论[M].北京:地震出版社,1993,78-80.
[5]陆远忠,陈章立.地震预报的地震学方法[M].北京:地震出版社,1985,175-196.
[6]啜永清,宋美琴.山西大同盆地震源机制解矛盾符号比及波速比变化的研究[J].山西地震,2005,109(2):1-3.
[7]赵晋明,胡毅力,杨润海,等,岩石临破前波速奇异变化的再研究[J].地震研究,2001,24(2):136-139.
[8]张成科,张先康,赵金仁,等.渤海湾及其邻区壳幔速度结构研究与综述[J].地震学报,2002,24(4):428-435.
[9]祝治平,张先康,盖玉杰,等.邢台震源区及其邻近地区地壳上地幔速度结构研究[J].地震学报,1992,27(3):328-334.
[10]黎明晓,张晓东.应用多台法测定华北地区地壳的平均波速比[J].地震,2004,24(1):163-169.
[11]冯益德.地震波速比异常[M].北京:地震出版社.1981.
[12]杨明桂,王昆.江西省地质构造及地壳演化[J].江西地质,1994,8(4):239-251.
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