利用地震剖面研究夏垫断裂西南段的活动性
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摘要
地震方法是针对厚覆盖区城市直下型活动断裂的一种不可替代的探测技术,对于不同的探测深度需采用不同的排列长度。为研究夏垫断裂在远离三河-平谷8.0级地震震源区的活动性,我们在该震源区SW方向约30km处开展了中浅层反射地震探测试验,并跨过中浅层地震探测到的夏垫断裂进行了浅层反射地震探测试验。浅层和中浅层地震探测的试验结果表明,在5m道间距的地震剖面上,在200m深度以下夏垫断裂得到了较好的反映,在该深度以上,该断裂反映不明显;在2m道间距的地震剖面上,夏垫断裂错断明显,但剖面上的最浅一组反射波(深度约30m)却没有发生明显错断。由此得出:距1679年三河-平谷8.0级地震震源位置SW方向约30km处,夏垫断裂的活动性减弱。
Seismic method is a necessary exploration method for detecting active faults buried directly beneath major cities in deep coverage area.Different array length must be adopted for different detecting depth.The Xiadian Fault is a seismogenic fault and related to the 1679 Sanhe-Pinggu earthquake(M=8.0).The deep and moderate-deep structural characteristics of the fault are revealed from the deep and moderate-deep seismic profiles across the fault.To research the activity of the fault away from the earthquake region,moderate-shallow seismic reflection detection experiment was developed with the working parameters as 5m group interval,15m offset,10 folds,60 active receiving channels,single-ended spread shooting by Wacker source,and one point receiving by 40Hz geophones.Based on the results of moderate-shallow seismic detection,a shallow seismic profile was laid across the fault detected by moderate-shallow seismic profiling.The shallow seismic reflection detection experiment was developed by using 2m group interval and hammer source as well as other ways similar to the moderate-shallow seismic reflection.It shows by the results of moderate-shallow and shallow seismic detection that the Xiadian Fault is well imaged at the depth below 200m on the seismic profile of 5m group interval,but it is invisible at the depth above 200m on the profile.The fault on the seismic profile of 2m group interval is obvious,but the shallowest reflection(depth about 30m)on the profile is uninterrupted.It can be educed that the activity of Xiadian Fault weakens about 30km southwest of the epicenter of the 1679 M8.0 Sanhe-Pinggu earthquake.
Seismic method is a necessary exploration method for detecting active faults buried directly beneath major cities in deep coverage area.Different array length must be adopted for different detecting depth.The Xiadian Fault is a seismogenic fault and related to the 1679 Sanhe-Pinggu earthquake(M=8.0).The deep and moderate-deep structural characteristics of the fault are revealed from the deep and moderate-deep seismic profiles across the fault.To research the activity of the fault away from the earthquake region,moderate-shallow seismic reflection detection experiment was developed with the working parameters as 5m group interval,15m offset,10 folds,60 active receiving channels,single-ended spread shooting by Wacker source,and one point receiving by 40Hz geophones.Based on the results of moderate-shallow seismic detection,a shallow seismic profile was laid across the fault detected by moderate-shallow seismic profiling.The shallow seismic reflection detection experiment was developed by using 2m group interval and hammer source as well as other ways similar to the moderate-shallow seismic reflection.It shows by the results of moderate-shallow and shallow seismic detection that the Xiadian Fault is well imaged at the depth below 200m on the seismic profile of 5m group interval,but it is invisible at the depth above 200m on the profile.The fault on the seismic profile of 2m group interval is obvious,but the shallowest reflection(depth about 30m)on the profile is uninterrupted.It can be educed that the activity of Xiadian Fault weakens about 30km southwest of the epicenter of the 1679 M8.0 Sanhe-Pinggu earthquake.
引文
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张先康,赵金仁,刘国华,等.2002.三河-平谷8.0级大震区震源细结构的深地震反射探测研究[J].中国地震,18(4):326—336.ZHANG Xian-kang,ZHAO Jin-ren,LIU Guo-hua,et al.2002.Study on fine crustal structure of the Sanhe-Pingguearthquake(M8.0)region by deep seismic reflection profiling[J].Earthquake Research in China,18(4):326—336(in Chinese).
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高景华,徐明才.2004.地震反射方法探测城市活断层中的几个问题[J].地质与勘探,40(增刊):91—95.GAO Jing-hua,XU Ming-cai.2004.Some problems in detecting active faults using seismic reflection method[J].Ge-ology and Prospecting,40(Suppl):91—95(in Chinese).
马文涛,唐文榜,徐锡伟,等.2005.北京黄庄-高丽营隐伏断裂立水桥段浅部活动特征的地震探测[J].物探与化探,29(6):503—505.MA Wen-tao,TANG Wen-bang,XU Xi-wei,et al.2005.Seismic exploration of shallow deformation along Lishuiqiaosection of Huangzhuang-Gaoliying active fault in Beijing urban area[J].Geophysical and Geochemical Explora-tion,29(6):503—505(in Chinese).
王庆海,徐明才.1991.抗干扰高分辨率浅层地震勘探[M].北京:地质出版社.40—211.WANG Qing-hai,XU Ming-cai.1991.Anti-interference High-resolution ShallowSeismic Exploration[M].GeologicalPublishing House,Beijing.40—211(in Chinese).
徐明才,高景华,柴铭涛,等.1998.地震方法在断层活动性评价中的应用研究[J].地震学报,20(3):279—284.XU Ming-cai,GAO Jing-hua,CHAI Ming-tao,et al.1998.Application research of seismic method in assessment of ac-tive fault[J].Acta Seismologica Sinica,20(3):279—284(in Chinese).
徐锡伟,吴卫民,张先康,等.2002.首都圈地区地壳最新构造变动与地震[M].北京:科学出版社.118—133.XUXi-wei,WUWei-min,ZHANG Xian-kang,et al.2002.The Latest Crustal Deformation and Earthquakes in Beijingarea[M].Science Press,Beijing.118—133(in Chinese).
徐明才,高景华,刘建勋,等.2005.应用于城市活断层调查的地震方法技术[J].中国地震,21(1):17—23.XU Ming-cai,GAO Jing-hua,LIU Jian-xun,et al.2005.Application of the seismic method to detecting active faults[J].Earthquake Research in China,21(1):17—23(in Chinese).
张先康,赵金仁,刘国华,等.2002.三河-平谷8.0级大震区震源细结构的深地震反射探测研究[J].中国地震,18(4):326—336.ZHANG Xian-kang,ZHAO Jin-ren,LIU Guo-hua,et al.2002.Study on fine crustal structure of the Sanhe-Pingguearthquake(M8.0)region by deep seismic reflection profiling[J].Earthquake Research in China,18(4):326—336(in Chinese).
Williams R A,Odum J K,Pratt T L,et al.1995.Seismic surveys assess earthquake hazard in the New Madrid area[J].The Leading Edge,14:30—34.
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