藏南地区中深源地震精确定深研究及其地球动力学含义
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摘要
利用2004-2005年Hi-CLIMB计划架设在藏南日喀则附近由28台宽频带数字地震仪组成的二维台阵的地震记录,应用双差层析定位方法(TomoDD)对454个区域地震进行了精确重定位,共确定了340个地震的精确位置.发现区域震源深度呈明显的双层分布,其中有21个地震的深度在50-80 km之间,与该地区的莫霍面深度相近.通过不同深度震源的理论地震图与实际地震图对比的方法,发现震源位置位于莫霍面上下地震图的震相存在明显差异,从而给出了存在地幔地震的直接观测证据.这一发现,对长期争论的地幔地震是否存在及大陆岩石圈流变结构的"三明治"模型有重要参考意义.
We have relocated accurately 340 local earthquakes from an earthquake catalogue containing 454 local earthquakes using TomoDD method. The data for relocation came from a 2-D seismic array near Xigaze out of Hi-CLIMB project. This array contained 28 broad band seismometers and recorded continuous seismic data from 2004 to 2005. We found the earthquakes were relocated in two separate layers. One layer is near the Earth space, the other is near the Moho. Totally, 21 earthquakes have been relocated at depth of 50-80 km which was very near the Moho. In order to determine these deep earthquakes occurred in the upper mantle, we preformed the comparison between the real seismogram and the synthetic seismograms at different depth. We found that there was obvious difference between seismograms when the earthquake sources were above or beneath the Moho. As a result, we provided the direct evidence of the existence of mantle earthquake, which was very important for the controversy on the "sandwich" lithospheric rheology model.
We have relocated accurately 340 local earthquakes from an earthquake catalogue containing 454 local earthquakes using TomoDD method. The data for relocation came from a 2-D seismic array near Xigaze out of Hi-CLIMB project. This array contained 28 broad band seismometers and recorded continuous seismic data from 2004 to 2005. We found the earthquakes were relocated in two separate layers. One layer is near the Earth space, the other is near the Moho. Totally, 21 earthquakes have been relocated at depth of 50-80 km which was very near the Moho. In order to determine these deep earthquakes occurred in the upper mantle, we preformed the comparison between the real seismogram and the synthetic seismograms at different depth. We found that there was obvious difference between seismograms when the earthquake sources were above or beneath the Moho. As a result, we provided the direct evidence of the existence of mantle earthquake, which was very important for the controversy on the "sandwich" lithospheric rheology model.
引文
[1] Chen W, Yang Z. Earthquakes beneath the Himalayas and Tibet; evidence for strong lithospheric mantle. Science,2004,304:1949-1952
[2] Molnar P, Chen W. Focal depths and fault plane solutions of earthquakes under the Tibetan Plateau. J. Geophys. Res. ,1983, 88:1180-1196
[3] Monsalve G, Sheehan A, Schulte-Pelkutn V, et al.Seismicity and one-dimensional velocity structure of the Himalayan collision zone: earthquakes in the crust and uppermantle. J. Geophys. Res. , 2006, 111: B10301, doi: 10． 1029/2005JB004062
[4] Zhu L, Helmberger D V. Intermediate depth earthquakes beneath the Indian-Tibet collision zone. Geophys. Res.Lett. , 1996,23(5) :435-438
[5] Chen W P, Molnar P. Focal depths of intracontinental and intraplate earthquakes and their implications for the thermal and mechanical properties of the lithosphere. J. Geophys.Res. , 1983,88(B5) :4183-4214
[6] Jackson J. Faulting, flow, and the strength of the continental lithosphere. Int. Geol. Rev., 2002,44(1) :39-61
[7] Jackson J A, Austrheim H, McKenzie D, et al.Metastability, mechanical strength, and the support of mountain belts. Geology, 2004,32(7) :625-628
[8] Lomnitz C. Three theorems of earthquake location. Bull.Seismol. Soc. Am. ,2006 ,96(1) : 306-312
[9] Liang X, Zhou S, Chen Y J , et al. Earthquake distribution in southern Tibet and its tectonic implications. J. Geophys.Res. ,2008, 113(B12) :B12409 ,doi: 10． 1029/2007JB005101
[10] Zhang H, Thurber C H. Double-difference tomography: the method and its application to the Hay ward fault, California.Bull. Seismol. Soc. Am., 2003,93:1875-1889
[11] Waldhauser F, Ellsworth W L. A double-difference earthquake location algorithm: method and application to theNorthern Hayward fault, California. Bull. Seismol. Soc.Am. ,2000,90:1353-1368
[12] 朱艾斓,徐锡伟,周永胜等.川西地区小震重新定位及其活动构造意义.地球物理学报,2005,48(3) :629-636 Zhu A L, Xu X W, Zhou Y S, et al. Relocation of small earthquakes in western Sichuan, China and its implications for active tectonics. Chinese J. Geophys. (in Chinese) ,2005,48(3) :629-636
[13] 黄媛,杨建思,张天中.2003年新疆巴楚-伽师地震序列的双差法重新定位研究.地球物理学报,2006． 49(1) :162-169 Huang Y, Yang J S, Zhang T Z. Relocation of the Bachu Jiashi, Xinjiang earthquake sequence in 2003 using the double difference location algorithm. Chinese J. Geophys. (in Chinese), 2006, 49( 1) :162-169
[14] 李乐,陈棋福,陈颙.首都圈地震活动构造成因的小震精定位分析.地球物理学进展,2007,22(1) :24-34 Li L, Chen Q F, Chen Y. Relocated seismicity in Big Beijing area and its tectonic implication. Progress in Geophysics (in Chinese), 2007, 22(1) :24-34
[15] Ni J, Barazangi M. Seismotectonics of the Himalayan collision zone: geometry of the underthrusting India plate beneath the Himalaya. J. Geophys. Res. , 1984, 89: 1147-1163
[16] Zhao L, Helmberger D, Geophysical implication from relocation of Tibetan earthquakes-hot lithosphere. Geophys. Res. Lett., 1991,18:2205-2208
[17] Mooney W D, Laske G, Masters T G. Crust 5． 1: a global crustal model at 5×5 degrees. J. Geophys. Res. .1998 ,103 :727-747
[18] Rapine R, Tilmann F, West M, et al. Crustal structure of northern and southern Tibet from surface wave dispersion analysis. J. Geophys. Res., 2003, 108 (B2) : 2120, doi: 10． 1029/2001JB000445
[19] Tan Y, Zhu L, Helmberger D V, et al. Locating and modeling regional earthquakes with two stations. J. Geophys.Res., 2006, 111:B01306, doi:10． 1029/2005JB003775
[20] Chen X F. A systematic and efficient method of computing normal modes for multilayered half-space. Geophys. J. Int. ,1993,115,391-409
[21] Xu Z H, Wang S Y, Huang Y R, et al. Tectonic stress field of China inferred from a large number of small earthquakes.J. Geophys. Res. ,1992,97(B8) : 11867-11877
[2] Molnar P, Chen W. Focal depths and fault plane solutions of earthquakes under the Tibetan Plateau. J. Geophys. Res. ,1983, 88:1180-1196
[3] Monsalve G, Sheehan A, Schulte-Pelkutn V, et al.Seismicity and one-dimensional velocity structure of the Himalayan collision zone: earthquakes in the crust and uppermantle. J. Geophys. Res. , 2006, 111: B10301, doi: 10． 1029/2005JB004062
[4] Zhu L, Helmberger D V. Intermediate depth earthquakes beneath the Indian-Tibet collision zone. Geophys. Res.Lett. , 1996,23(5) :435-438
[5] Chen W P, Molnar P. Focal depths of intracontinental and intraplate earthquakes and their implications for the thermal and mechanical properties of the lithosphere. J. Geophys.Res. , 1983,88(B5) :4183-4214
[6] Jackson J. Faulting, flow, and the strength of the continental lithosphere. Int. Geol. Rev., 2002,44(1) :39-61
[7] Jackson J A, Austrheim H, McKenzie D, et al.Metastability, mechanical strength, and the support of mountain belts. Geology, 2004,32(7) :625-628
[8] Lomnitz C. Three theorems of earthquake location. Bull.Seismol. Soc. Am. ,2006 ,96(1) : 306-312
[9] Liang X, Zhou S, Chen Y J , et al. Earthquake distribution in southern Tibet and its tectonic implications. J. Geophys.Res. ,2008, 113(B12) :B12409 ,doi: 10． 1029/2007JB005101
[10] Zhang H, Thurber C H. Double-difference tomography: the method and its application to the Hay ward fault, California.Bull. Seismol. Soc. Am., 2003,93:1875-1889
[11] Waldhauser F, Ellsworth W L. A double-difference earthquake location algorithm: method and application to theNorthern Hayward fault, California. Bull. Seismol. Soc.Am. ,2000,90:1353-1368
[12] 朱艾斓,徐锡伟,周永胜等.川西地区小震重新定位及其活动构造意义.地球物理学报,2005,48(3) :629-636 Zhu A L, Xu X W, Zhou Y S, et al. Relocation of small earthquakes in western Sichuan, China and its implications for active tectonics. Chinese J. Geophys. (in Chinese) ,2005,48(3) :629-636
[13] 黄媛,杨建思,张天中.2003年新疆巴楚-伽师地震序列的双差法重新定位研究.地球物理学报,2006． 49(1) :162-169 Huang Y, Yang J S, Zhang T Z. Relocation of the Bachu Jiashi, Xinjiang earthquake sequence in 2003 using the double difference location algorithm. Chinese J. Geophys. (in Chinese), 2006, 49( 1) :162-169
[14] 李乐,陈棋福,陈颙.首都圈地震活动构造成因的小震精定位分析.地球物理学进展,2007,22(1) :24-34 Li L, Chen Q F, Chen Y. Relocated seismicity in Big Beijing area and its tectonic implication. Progress in Geophysics (in Chinese), 2007, 22(1) :24-34
[15] Ni J, Barazangi M. Seismotectonics of the Himalayan collision zone: geometry of the underthrusting India plate beneath the Himalaya. J. Geophys. Res. , 1984, 89: 1147-1163
[16] Zhao L, Helmberger D, Geophysical implication from relocation of Tibetan earthquakes-hot lithosphere. Geophys. Res. Lett., 1991,18:2205-2208
[17] Mooney W D, Laske G, Masters T G. Crust 5． 1: a global crustal model at 5×5 degrees. J. Geophys. Res. .1998 ,103 :727-747
[18] Rapine R, Tilmann F, West M, et al. Crustal structure of northern and southern Tibet from surface wave dispersion analysis. J. Geophys. Res., 2003, 108 (B2) : 2120, doi: 10． 1029/2001JB000445
[19] Tan Y, Zhu L, Helmberger D V, et al. Locating and modeling regional earthquakes with two stations. J. Geophys.Res., 2006, 111:B01306, doi:10． 1029/2005JB003775
[20] Chen X F. A systematic and efficient method of computing normal modes for multilayered half-space. Geophys. J. Int. ,1993,115,391-409
[21] Xu Z H, Wang S Y, Huang Y R, et al. Tectonic stress field of China inferred from a large number of small earthquakes.J. Geophys. Res. ,1992,97(B8) : 11867-11877
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