利用地震和爆破资料反演宁夏及邻区浅层三维速度结构
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摘要
将有限差分正演及LSQR反演方法应用到宁夏及邻区,利用该区2003—2009年7年间的地震和爆破记录,经过重新细致分析,得到了具有4个以上台站清楚记录到初至波Pg和Pn到时的地震426次、爆破52次,剔除到时离散较大的数据后共有2788条记录.获得了不同深度的速度平面分布图像以及不同位置的深度速度剖面图像.得出深度0—5km的平均速度约为5.1km/s,深度5—25km的平均速度约为5.9km/s,深度25—30km的平均速度约为6.4km/s;浅层低速层主要分布在银川地堑、中卫清水河盆地,高速层主要分布在银川地堑西部的贺兰山区.此结论与该地区地质结构相符.深层高速层在中卫—同心断裂带一带最为显著,低速层主要分布在银川地堑及以西部分地区、固原清水河断裂带等.
We applied the finite difference and LSQR inversion algorithm to the seismic data in Ningxia and adjacent region. We collected Pg and Pn first arrival data from 426 earthquakes and 52 explosions occurred during the 7 years of 2003—2009. By excluding the data with large scattering we obtained 2788 arrival time readings. Inverting these data gives the velocity image on horizontal planes at different depth and the image on some vertical profiles. By referring relevant geological materials and some previous studies we have drawn the following conclusion:the average P-wave velocity for the depth range of 0—5 km is 5.1 km/s, the average velocity for 5—25 km is 5.9 km/s, while that for 25—35 km reaches to 6.4 km/s. In the shallow part the low velocity zones are mainly in Yinchuan graben basin and Qingshui river basin in Zhongwei county, while a major high velocity zone locates in Helan mountain area. In the deep crust a high velocity zone is seen along the Zhongwei-Tongxin fault zone, while low velocity zone lies mainly in the Yinchuan graben and its west, and in Guyuan Qingshui river fault zone. This conclusion is basically consistent with the result of previous studies.
We applied the finite difference and LSQR inversion algorithm to the seismic data in Ningxia and adjacent region. We collected Pg and Pn first arrival data from 426 earthquakes and 52 explosions occurred during the 7 years of 2003—2009. By excluding the data with large scattering we obtained 2788 arrival time readings. Inverting these data gives the velocity image on horizontal planes at different depth and the image on some vertical profiles. By referring relevant geological materials and some previous studies we have drawn the following conclusion:the average P-wave velocity for the depth range of 0—5 km is 5.1 km/s, the average velocity for 5—25 km is 5.9 km/s, while that for 25—35 km reaches to 6.4 km/s. In the shallow part the low velocity zones are mainly in Yinchuan graben basin and Qingshui river basin in Zhongwei county, while a major high velocity zone locates in Helan mountain area. In the deep crust a high velocity zone is seen along the Zhongwei-Tongxin fault zone, while low velocity zone lies mainly in the Yinchuan graben and its west, and in Guyuan Qingshui river fault zone. This conclusion is basically consistent with the result of previous studies.
引文
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杨明芝,马禾青,廖玉华.2007.宁夏地震活动与研究[M].北京:地震出版社:11-46.
Vidale J E.1990.Finite-difference calculation of travel times in three dimensions[J].Geophysics,55(5):521-526.
Zelt C A,Barton P J.1998.Three-dimensional seismic refraction tomography:A comparison of two methods applied to data from the Faeroe Basin[J].J Geophys Res,103(B4):7187-7210.
国家地震局地学断面编委会.1992b.青海门源至福建宁德地学断面(说明书)[M].北京:地震出版社:1-5.
金延龙,杨明芝,赵卫明,施行觉,许文俊,李光泉.1999.利用区域台网记录的直达波、反射和折射波反演宁夏及邻区地壳P波三维速度结构[J].地震学报,21(4):394-401.
李松林,张先康,张成科,赵金仁,成双喜.2002.玛沁—兰州—靖边地震测深剖面地壳速度结构的初步研究[J].地球物理学报,45(2):210-217.
李松林,张先康,任青芳,张成科,石金虎,赵金仁,刘宝峰,潘素珍,张建狮,刘建军.2001.西吉—中卫地震测深剖面及其解释[J].地震地质,23(1):86-92.
孟广魁.1994.银川平原地震区划研究[M].银川:宁夏人民出版社:22-25.
王绒霞.1985.宁夏地区地震走时表[M].北京:中国科学院冰川冻土研究所内部资料:1-32.
莘海亮.2008.地震层析成像技术方法研究[D].兰州:中国地震局兰州地震研究所:1-2,18-19.
杨明芝,马禾青,廖玉华.2007.宁夏地震活动与研究[M].北京:地震出版社:11-46.
Vidale J E.1990.Finite-difference calculation of travel times in three dimensions[J].Geophysics,55(5):521-526.
Zelt C A,Barton P J.1998.Three-dimensional seismic refraction tomography:A comparison of two methods applied to data from the Faeroe Basin[J].J Geophys Res,103(B4):7187-7210.
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