尼泊尔—喜马拉雅地区中上地壳噪声成像
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摘要
本文利用HIMNT台网1年左右的宽频带连续波形记录,利用背景噪声信息的互相关函数提取了6～26 s的瑞利波相速度频散曲线,并反演得到了尼泊尔—喜马拉雅地区中上地壳横波速度结构.成像结果显示尼泊尔—喜马拉雅下方存在10 km左右厚的横波低速层(也是相对的低密度层).根据分析,我们认为这一相对低速度层对应了下插的印度地壳和上伏的喜马拉雅构造楔之间的滑脱面——MHT(Main Himalayan Thrust)附近的高温层.两大板块间沿着滑脱面MHT处摩擦产热,由于较低的热传导,热量积累导致了10 km厚的高温层,初步估算高喜马拉雅和特提斯喜马拉雅交界处下方MHT处温度高达,因此我们认为在高喜马拉雅下方MHT界面可能已经处于蠕滑状态,或者处于蠕滑-黏滑的过渡状态.这也解释了喜马拉雅地区的历史大地震为什么多发生在高喜马拉雅以南一侧.
Using the wide-band continuous wave record of HIMNT network for about 1 year, the cross correlation functions of the background noise information are calculated. Then we extract velocity dispersion curves of the Rayleigh wave phase of 6～26 s, and invert transverse wave velocity structure of the Nepal-Himalayas. The imaging results shows that there is a low velocity layer of about 10 km thick beneath the Nepal-Himalaya. According to the analysis, we think that this relatively low velocity layer corresponds to the high temperature zone near the detachment—MHT(Main Himalayan Thrust) between the lower part of the India crust and the upper Himalaya orogenic belt. A large amount of heat generated by the friction between the plates along MHT was produced. The heat accumulation resulted in a 10 km thick layer of high temperature because of the lower heat conduction. It is preliminarily estimated that the temperature of MHT under the junction of the High-Himalaya and the Tethyan-Himalaya is up to,we infer that MHT below the High Himalaya is in brittle-ductile transition state or ducile state. This also explains why great earthquakes in Himalaya occurred to the south of the high Himalaya.
Using the wide-band continuous wave record of HIMNT network for about 1 year, the cross correlation functions of the background noise information are calculated. Then we extract velocity dispersion curves of the Rayleigh wave phase of 6～26 s, and invert transverse wave velocity structure of the Nepal-Himalayas. The imaging results shows that there is a low velocity layer of about 10 km thick beneath the Nepal-Himalaya. According to the analysis, we think that this relatively low velocity layer corresponds to the high temperature zone near the detachment—MHT(Main Himalayan Thrust) between the lower part of the India crust and the upper Himalaya orogenic belt. A large amount of heat generated by the friction between the plates along MHT was produced. The heat accumulation resulted in a 10 km thick layer of high temperature because of the lower heat conduction. It is preliminarily estimated that the temperature of MHT under the junction of the High-Himalaya and the Tethyan-Himalaya is up to,we infer that MHT below the High Himalaya is in brittle-ductile transition state or ducile state. This also explains why great earthquakes in Himalaya occurred to the south of the high Himalaya.
引文
Ambraseys N N,Douglas J. 2004. Magnitude calibration of north Indian earthquakes [J]. Geophys. J. Int.,159(1): 165-206.
Backus G,Gilbert F. 1968. The resolving power of gross Earth data [J]. Geophys. J. Int.,16(2): 169-205.
Bilham R,Gaur V K,Molnar P. 2001. Himalayan seismic hazard [J]. Science,293(5534): 1442-1444.
Cattin R,Martelet G,Henry P,et al. 2001. Gravity anomalies,crustal structure and thermo-mechanical support of the Himalaya of Central Nepal [J]. Geophys. J. Int.,147(2): 381-392.
Chaye′ d’Albissin,M. & Sirieys,P.,1989. Thermal deformability of rocks: relation to rock structure,in Rock at Great Depth,pp. 363-370,eds Maury,V. & Fourmaintraux,D.,A. A. Balkema,Rotterdam.
Ditmar P G,Yanovskaya B. 1987. Generalization of Backus-Gilbert method for restimation of lateral variations of surface wave velocities [J]. Izv. Phys. Solid Earth.,23(6): 470- 477.
Elliott J R,Jolivet R,González P J,et al. 2016. Himalayan megathrust geometry and relation to topography revealed by the Gorkha earthquake [J]. Nature geoscience. 9(2): 174-180.
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Henry P,Pichon X L,Goffe B. 1997. Kinematic,thermal and petrological model of the Himalayas:constraints related to metamorphism within the underthrust Indian crust and topographic elevation [J]. Tectonophysics,273(1-2): 31-56.
Herrmann R B,Ammon C J,Surface waves,receiver functions and crustal structure. Computer Programs in Seismology,Version3.30,SaintLouis University. 2004,http://www.eas.slu.edu/People/RBHerrmann/CPS330.html.
Hetényi G,Cattin R,Vergne J,et al. 2006. The effective elastic thickness of the India Plate from receiver function imaging,gravity anomalies and thermomechanical modelling [J]. Geophys. J. Internat. 167(3): 1106-1118.
Jeanloz R,Knittle E. 1986. Chemistry and Physics of Terrestrial Planets,pp. 275-309,Springer Verlag,New York.
Li C,Hilst R D v d,Meltzer A S,et al. 2008. Subduction of the Indian lithosphere beneath the Tibetan Plateau and Burma [J]. Earth Planet. Sci. Lett.,274(1-2): 157-168.
Liang X F,Yang S,Chen Y,et al. 2011. Crustal and mantle velocity models of southern Tibet from finite frequency tomography [J]. Journal of Geophysical Research,116(B2).
Lobkis O I,Weaver R L.2001. On the emergence of the Green’s function in the correlations of a diffuse field [J]. J. acoust. Soc. Am.,110: 3011-3017.
Lu L Y,He Z Q,Ding Z F,et al. 2014. Azimuth anisotropy and velocity heterogeneity of Yunnan area based on seismic ambient noise [J]. Chinese Journal of Geophysics (in Chinese),57(3): 822-836,doi: 10.6038/cjg20140312.鲁来玉,何正勤,丁志峰,等. 2014. 基于背景噪声研究云南地区面波速度非均匀性和方位各向异性[J]. 地球物理学报,57(3): 822-836,doi: 10.6038/cjg20140312.
Lyon-Caen H,Molnar P. 1983. Constraints on the structure of the Himalaya from an analysis of gravity anomalies and a flexural model of the lithosphere [J]. J. Geophys. Res.,88(B10): 8171-8191.
Pan J T,Li Y H,Wu Q J,et al. 2015. Phase velocity maps of Rayleigh waves in the southeast Tibetan plateau [J]. Chinese Journal of Geophysics (in Chinese),58(11): 3993- 4006,doi: 10.6038/cjg20151109.潘佳铁,李永华,吴庆举,等. 2015. 青藏高原东南部地区瑞雷波相速度层析成像[J]. 地球物理学报,58(11): 3993- 4006,doi: 10.6038/cjg20151109.
Ritzwoller M H,Levshin A L. 1998. Eurasian surface wave tomography: Group velocities [J]. J. Geophys. Res.,103(B3): 4839- 4878.
Roux P,Sabra K G,Kuperman WA. 2005. Ambient noise cross correlation in free space: theoretical approach [J]. J. acoust. Soc. Am.,117: 79-84.
Schulte-Pelkum V,Monsalve G,Sheehan A,et al. 2005. Imaging the Indian subcontinent beneath the Himalaya [J]. Nature,435: 1222-1225.
Shearer P M. 2009. Introduction to Seismology,Cambridge Univ. Press.
Wang X L,Ma S L,Guo Z,et al. 2013. S-wave velocity of the crust in Three Gorges Reservoir and the adjacent region inverted from seismic ambient noise tomography [J]. Chinese Journal of Geophysics (in Chinese),56(12): 4113- 4124,doi: 10.6038/cjg20131216.王小龙,马胜利,郭志,等. 2013. 利用地震背景噪声成像技术反演三峡库区及邻近地区地壳剪切波速度结构[J]. 地球物理学报,56(12): 4113- 4124,doi: 10.6038/cjg20131216.
Weaver R L,Lobkis O I.2004. Diffuse fields in open systems and the emergence of the Green’s function (L) [J]. The Journal of the Acoustical Society of America,116: 2731.
Wu F T,Levshin A. 1994. Surface-wave group velocity tomography of East Asia [J]. Phys. Earth.Planet. Inter.,84(1- 4): 59-77.
Yanovskaya T B,Ditmar P G. 1990. Smoothness criteria in surface wave tomography [J]. Geophys. J. Int.,102(1): 63-72.
Yao H J,Van der Hilst R D,de Hoop M V. 2006. Surface-wave array tomography in SE Tibet from ambient seismic noise and two-station analysis—I. Phase velocity maps [J]. Geophys. J. Int.,166(2): 732-744.
Zhao W J,Nelson K D,Che J,et al. 1993. Deep seismic-reflection evidence for continental underthrusting beneath southern Tibet [J]. Nature,366: 557-559.
滕吉文,阮小敏,张永谦,等. 2012. 青藏高原地壳与上地幔成层速度结构与深部层间物质的运移轨迹[J]. 岩石学报,28(12): 4077- 4100.
王琼,高原.2014. 青藏东南缘背景噪声的瑞利波相速度层析成像及强震活动[J]. 中国科学:地球科学,44(11): 2440-2450.
郑定昌,盖增喜,杨润海,等. 2014. 云南地区背景噪声层析成像[J]. 地震学报,36(4): 602- 614.
Backus G,Gilbert F. 1968. The resolving power of gross Earth data [J]. Geophys. J. Int.,16(2): 169-205.
Bilham R,Gaur V K,Molnar P. 2001. Himalayan seismic hazard [J]. Science,293(5534): 1442-1444.
Cattin R,Martelet G,Henry P,et al. 2001. Gravity anomalies,crustal structure and thermo-mechanical support of the Himalaya of Central Nepal [J]. Geophys. J. Int.,147(2): 381-392.
Chaye′ d’Albissin,M. & Sirieys,P.,1989. Thermal deformability of rocks: relation to rock structure,in Rock at Great Depth,pp. 363-370,eds Maury,V. & Fourmaintraux,D.,A. A. Balkema,Rotterdam.
Ditmar P G,Yanovskaya B. 1987. Generalization of Backus-Gilbert method for restimation of lateral variations of surface wave velocities [J]. Izv. Phys. Solid Earth.,23(6): 470- 477.
Elliott J R,Jolivet R,González P J,et al. 2016. Himalayan megathrust geometry and relation to topography revealed by the Gorkha earthquake [J]. Nature geoscience. 9(2): 174-180.
Gao X,Wang K L. 2017. Rheological separation of the megathrust seismogenic zone and episodic tremor and slip [J]. Nature,543: 416- 419.
Henry P,Pichon X L,Goffe B. 1997. Kinematic,thermal and petrological model of the Himalayas:constraints related to metamorphism within the underthrust Indian crust and topographic elevation [J]. Tectonophysics,273(1-2): 31-56.
Herrmann R B,Ammon C J,Surface waves,receiver functions and crustal structure. Computer Programs in Seismology,Version3.30,SaintLouis University. 2004,http://www.eas.slu.edu/People/RBHerrmann/CPS330.html.
Hetényi G,Cattin R,Vergne J,et al. 2006. The effective elastic thickness of the India Plate from receiver function imaging,gravity anomalies and thermomechanical modelling [J]. Geophys. J. Internat. 167(3): 1106-1118.
Jeanloz R,Knittle E. 1986. Chemistry and Physics of Terrestrial Planets,pp. 275-309,Springer Verlag,New York.
Li C,Hilst R D v d,Meltzer A S,et al. 2008. Subduction of the Indian lithosphere beneath the Tibetan Plateau and Burma [J]. Earth Planet. Sci. Lett.,274(1-2): 157-168.
Liang X F,Yang S,Chen Y,et al. 2011. Crustal and mantle velocity models of southern Tibet from finite frequency tomography [J]. Journal of Geophysical Research,116(B2).
Lobkis O I,Weaver R L.2001. On the emergence of the Green’s function in the correlations of a diffuse field [J]. J. acoust. Soc. Am.,110: 3011-3017.
Lu L Y,He Z Q,Ding Z F,et al. 2014. Azimuth anisotropy and velocity heterogeneity of Yunnan area based on seismic ambient noise [J]. Chinese Journal of Geophysics (in Chinese),57(3): 822-836,doi: 10.6038/cjg20140312.鲁来玉,何正勤,丁志峰,等. 2014. 基于背景噪声研究云南地区面波速度非均匀性和方位各向异性[J]. 地球物理学报,57(3): 822-836,doi: 10.6038/cjg20140312.
Lyon-Caen H,Molnar P. 1983. Constraints on the structure of the Himalaya from an analysis of gravity anomalies and a flexural model of the lithosphere [J]. J. Geophys. Res.,88(B10): 8171-8191.
Pan J T,Li Y H,Wu Q J,et al. 2015. Phase velocity maps of Rayleigh waves in the southeast Tibetan plateau [J]. Chinese Journal of Geophysics (in Chinese),58(11): 3993- 4006,doi: 10.6038/cjg20151109.潘佳铁,李永华,吴庆举,等. 2015. 青藏高原东南部地区瑞雷波相速度层析成像[J]. 地球物理学报,58(11): 3993- 4006,doi: 10.6038/cjg20151109.
Ritzwoller M H,Levshin A L. 1998. Eurasian surface wave tomography: Group velocities [J]. J. Geophys. Res.,103(B3): 4839- 4878.
Roux P,Sabra K G,Kuperman WA. 2005. Ambient noise cross correlation in free space: theoretical approach [J]. J. acoust. Soc. Am.,117: 79-84.
Schulte-Pelkum V,Monsalve G,Sheehan A,et al. 2005. Imaging the Indian subcontinent beneath the Himalaya [J]. Nature,435: 1222-1225.
Shearer P M. 2009. Introduction to Seismology,Cambridge Univ. Press.
Wang X L,Ma S L,Guo Z,et al. 2013. S-wave velocity of the crust in Three Gorges Reservoir and the adjacent region inverted from seismic ambient noise tomography [J]. Chinese Journal of Geophysics (in Chinese),56(12): 4113- 4124,doi: 10.6038/cjg20131216.王小龙,马胜利,郭志,等. 2013. 利用地震背景噪声成像技术反演三峡库区及邻近地区地壳剪切波速度结构[J]. 地球物理学报,56(12): 4113- 4124,doi: 10.6038/cjg20131216.
Weaver R L,Lobkis O I.2004. Diffuse fields in open systems and the emergence of the Green’s function (L) [J]. The Journal of the Acoustical Society of America,116: 2731.
Wu F T,Levshin A. 1994. Surface-wave group velocity tomography of East Asia [J]. Phys. Earth.Planet. Inter.,84(1- 4): 59-77.
Yanovskaya T B,Ditmar P G. 1990. Smoothness criteria in surface wave tomography [J]. Geophys. J. Int.,102(1): 63-72.
Yao H J,Van der Hilst R D,de Hoop M V. 2006. Surface-wave array tomography in SE Tibet from ambient seismic noise and two-station analysis—I. Phase velocity maps [J]. Geophys. J. Int.,166(2): 732-744.
Zhao W J,Nelson K D,Che J,et al. 1993. Deep seismic-reflection evidence for continental underthrusting beneath southern Tibet [J]. Nature,366: 557-559.
滕吉文,阮小敏,张永谦,等. 2012. 青藏高原地壳与上地幔成层速度结构与深部层间物质的运移轨迹[J]. 岩石学报,28(12): 4077- 4100.
王琼,高原.2014. 青藏东南缘背景噪声的瑞利波相速度层析成像及强震活动[J]. 中国科学:地球科学,44(11): 2440-2450.
郑定昌,盖增喜,杨润海,等. 2014. 云南地区背景噪声层析成像[J]. 地震学报,36(4): 602- 614.