东亚地区上地幔顶部P_n速度结构的构造动力学意义
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摘要
以东亚地区(15°～60°N,60°～145°E)为研究区,通过多种资料渠道收集了研究区内27777次地震在1354个地震台站记录到的296334条Pn波射线,反演了东亚地区上地幔顶部Pn速度结构及其横向变化,并进而探讨了Pn波速度结构横向变化的动力学意义。反演结果给出,东亚地区Pn波平均速度为8.03km/s。横向变化量从-0.42km/s至+0.41km/s。在研究区内,Pn速度和横向变化总体上呈现为东、西2个特征性分区。从太平洋板块边界到中国东部(大致为东经108°以东)为Pn速度偏低区,而东经108°以西为Pn速度偏高地区。这2个特征性差异分区分别与太平洋板块俯冲和印度洋板块碰撞挤压的动力学背景相一致。无论是东部地区还是西部地区,均显示活动构造区为Pn速度的相对低值异常区,而构造上稳定地区为Pn速度的高值异常区。并且在东、西部各自分区中,均呈现为地震活动水平与Pn速度之间成反向变化关系,显示了Pn速度横向变化与构造变形和地震活动强度的相关性,Pn速度的低值异常区往往是构造变形和强震活动活跃的地区。
In the paper,we use 296334 Pn rays from 27777 earthquakes recorded by 1354 seismic stations in the eastern Asia region,an area spanning from 15°N-60°N and 60°E-145°E,to invert the Pn velocity structure of uppermost mantle and its lateral variations. We also discuss the tectonic implication of the lateral variation based on the Pn velocity structure. Inversion results show that the mean velocity of Pn is 8.03km/s in the eastern Asia region. The lateral variation spans from -0.42km/s to 0.41km/s. Two different tectonic regions can be identified according to distributions of Pn velocity and its lateral variation. In the region from the boundary of the Pacific plate to the east of 108°E,i.e.the eastern China,Pn velocity is relatively low. In the region located at west of 108°E,Pn velocity is high. The different distribution of Pn velocity is consistent to the regional geodynamic background. The dominant geodynamic effect is subduction of the Pacific plate in the eastern China and collision of the Indian Ocean plate in the western China. At the same time,Pn velocity is relatively low in active tectonic regions and high in the stable tectonic regions. The Pn velocity also shows negative correlation to the regional seismicity. The higher of the seismicity,the lower of the Pn velocity,and vice versa. The negative correlation indicates the relationship of lateral variation of Pn velocity and tectonic deformation with seismicity level. The region with low Pn velocity usually is a region with high tectonic deformation and intensive seismicity.
In the paper,we use 296334 Pn rays from 27777 earthquakes recorded by 1354 seismic stations in the eastern Asia region,an area spanning from 15°N-60°N and 60°E-145°E,to invert the Pn velocity structure of uppermost mantle and its lateral variations. We also discuss the tectonic implication of the lateral variation based on the Pn velocity structure. Inversion results show that the mean velocity of Pn is 8.03km/s in the eastern Asia region. The lateral variation spans from -0.42km/s to 0.41km/s. Two different tectonic regions can be identified according to distributions of Pn velocity and its lateral variation. In the region from the boundary of the Pacific plate to the east of 108°E,i.e.the eastern China,Pn velocity is relatively low. In the region located at west of 108°E,Pn velocity is high. The different distribution of Pn velocity is consistent to the regional geodynamic background. The dominant geodynamic effect is subduction of the Pacific plate in the eastern China and collision of the Indian Ocean plate in the western China. At the same time,Pn velocity is relatively low in active tectonic regions and high in the stable tectonic regions. The Pn velocity also shows negative correlation to the regional seismicity. The higher of the seismicity,the lower of the Pn velocity,and vice versa. The negative correlation indicates the relationship of lateral variation of Pn velocity and tectonic deformation with seismicity level. The region with low Pn velocity usually is a region with high tectonic deformation and intensive seismicity.
引文
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张先康,李松林,王夫运,等.2003.青藏高原东北缘、鄂尔多斯和华北唐山震区的地壳结构差异:深地震测深的结果[J].地震地质,25(1):52—60.ZHANG Xian-kang,LI Song-lin,WANG Fu-yun,et al.2003.Differences of crustal structures in northeastern edge of Ti-bet plateau,Ordos and Tangshan earthquake region in North China:Results of deep seismic sounding[J].Seis-mology and Geology,25(1):52—60(in Chinese).
Hearn T M,WANG Su-yun,James F N,et al.2004.Uppermost mantle velocities beneath China and surrounding regions[J].J Geophys Res,109(B11301).
Hearn T M,Beghoul N,Barazangi M.1991.Tomography of the western United States from regional arrival times[J].JGeophys Res,96:16369—16381.
Hearn T M,Ni J F.1994.Pnvelocities beneath continental collision zones:The Turkish-Iran Plateau[J].Geophys JInt,117:273—283.
Hearn T M.1996.Anisotropic Pntomography in the western United States[J].J Geophys Res,101:8403—8414.
Sonder L J,England P C.1989.Effect of temperature dependent rheology on large-scale continental extension[J].Jour-nal of Geophysical Research,94:7603—7619.
许忠淮,汪素云,裴顺平.2003.青藏高原东北缘地区Pn波速度的横向变化[J].地震学报,25(1):24—31.XU Zhong-huai,WANG Su-yun,PEI Shun-ping.2003.Lateral variations in Pnvelocity beneath the northeast margin ofthe Tibetan plateau[J].Acta Seismologica Sinica,16(1):26—33.
王敏,李强,王凡,等.2011.全球定位系统测定的2011年日本宫城MW9.0地震远场同震位移[J].科学通报,56(20):1593—1596.WANG Min,LI Qiang,WANG Fan,et al.2011.Far-field coseismic displacements associated with the2011Tohoku-Okiearthquake in Japan observed by Global Positioning System[J].Chinese Sci Bull,56(23):2419—2425.
汪素云,Heam T M,许忠淮,等.2001.中国大陆上地幔顶部Pn速度变化特征[J].中国科学(D辑),31(6):1—6.WANG Su-yun,Hearn T M,XU Zhong-huai,et al.2002.Velocity structure of uppermost mantle beneath China continentfrom Pntomography[J].Science in China(Ser D),45(2):144—150.
张国民,马宏生,王辉,等.2004.中国大陆活动地块与强震活动关系[J].中国科学(D辑),34(7):591—599.ZHANG Guo-min,MA Hong-sheng,WANG Hui,et al.,2004.Correlation between active tectonic blocks and strongearthquake activity in Mainland China[J].Science in China(Ser D),34(7):591—599(in Chinese).
张培震,邓起东,张国民,等.2003.中国大陆的强震活动与活动地块[J].中国科学(D辑),33(增刊):12—20.ZHANG Pei-zhen,DENG Qi-dong,ZHANG Guo-min,et al.2003.Active tectonic blocks and strong earthquakes in thecontinent of China[J].Science in China(Ser D),46(z2):13—24.
张先康,李松林,王夫运,等.2003.青藏高原东北缘、鄂尔多斯和华北唐山震区的地壳结构差异:深地震测深的结果[J].地震地质,25(1):52—60.ZHANG Xian-kang,LI Song-lin,WANG Fu-yun,et al.2003.Differences of crustal structures in northeastern edge of Ti-bet plateau,Ordos and Tangshan earthquake region in North China:Results of deep seismic sounding[J].Seis-mology and Geology,25(1):52—60(in Chinese).
Hearn T M,WANG Su-yun,James F N,et al.2004.Uppermost mantle velocities beneath China and surrounding regions[J].J Geophys Res,109(B11301).
Hearn T M,Beghoul N,Barazangi M.1991.Tomography of the western United States from regional arrival times[J].JGeophys Res,96:16369—16381.
Hearn T M,Ni J F.1994.Pnvelocities beneath continental collision zones:The Turkish-Iran Plateau[J].Geophys JInt,117:273—283.
Hearn T M.1996.Anisotropic Pntomography in the western United States[J].J Geophys Res,101:8403—8414.
Sonder L J,England P C.1989.Effect of temperature dependent rheology on large-scale continental extension[J].Jour-nal of Geophysical Research,94:7603—7619.
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