腾冲火山区的地震层析成像及其构造意义
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摘要
利用滇西南临时台网和固定台站的地震数据反演了腾冲及邻近地区的P波速度结构,着重分析了腾冲火山区和龙陵7级地震震源区的地壳结构特点.研究结果表明,腾冲火山区下方10～20 km深度范围存在明显的低速区,其横向尺度大约在20～30 km之间;推测这一低速区代表了仍处于活动状态的壳内岩浆源,热流通道有可能通过腾冲断裂延伸至地壳深部.地壳速度结构自东向西的变化显示出与不同时期的火山活动的关系,腾冲东侧偏高的速度结构反映了龙川江一带上新世时期火山通道内冷凝固结的岩浆侵入体或不易挥发的高密度残留物质。腾冲西侧的低速异常揭示了更新世以来持续至今的岩浆作用和热流活动.龙陵7级地震震源区的地壳结构存在明显的横向非均匀性.M7.3级和M7.4级地震与怒江断裂和龙陵断裂两侧的结构差异密切相关,它们分别发生在高速区和低速区的分界附近.怒江断裂东侧和龙陵断裂西侧具有较高的速度,是震源区应力积累的主要载体;两断裂之间地壳速度明显偏低,有可能是多期次的岩浆侵入导致地壳结构强度降低,使得怒江断裂和龙陵断裂易于受构造应力作用而引发强烈地震,估计地震的震源深度在10～12 km之间.
Using earthquake data from a temporary network and other permanent stations in southwestern Yunnan,we inverted the P-wave velocity structure of Tengzhong and adjacent areas,with the aim to analyze the crustal structure of the Tengchong volcanoes and Longling M> 7 earthquake areas.Our results indicate that the Tengchong volcanic area is underlain by a prominent low-velocity zone at 10～20 km depth and with a lateral extent of 20～30 km.We infer that this low-velocity zone represents an active magma source and the heat flow channel may extend into the deep crust through the Tengchong fault.The W-E variation in the crustal structure is correlated with the volcanic activities in different periods.The high-velocity structure in eastern Tengchong reflects the cooled and solidified magma intrusions or high density remnants within the volcanic channels during Miocene-Pliocene,whereas the low-velocity zone of western Tengchong reveals the magmatic and heat flow activities from Pleistocene to present day.A strong lateral heterogeneity is observed in the crust structure of the Longling M>7 earthquake area.The occurrence of the M7.3 and M7.4 earthquakes are related to the structural variation across the Nu River fault and the Longling fault,both of which are located near velocity boundaries.The upper crust east of the Nu River fault and west of the Longling fault is characterized by high velocities,which is considered as a primary location for stress accumulation in the earthquake area;however,low velocities are observed in the region between the Nu River fault and the Longling fault.It implies that multiple magma intrusions probably decreased the rheologic strength in the crust.It is the distinct variation in the structure that made the Nu River fault and the Longling fault easy to produce seismic ruptures for the intense earthquakes under the effect of tectonic stress.We infer that these two earthquakes occurred at 10～12 km depth.
Using earthquake data from a temporary network and other permanent stations in southwestern Yunnan,we inverted the P-wave velocity structure of Tengzhong and adjacent areas,with the aim to analyze the crustal structure of the Tengchong volcanoes and Longling M> 7 earthquake areas.Our results indicate that the Tengchong volcanic area is underlain by a prominent low-velocity zone at 10～20 km depth and with a lateral extent of 20～30 km.We infer that this low-velocity zone represents an active magma source and the heat flow channel may extend into the deep crust through the Tengchong fault.The W-E variation in the crustal structure is correlated with the volcanic activities in different periods.The high-velocity structure in eastern Tengchong reflects the cooled and solidified magma intrusions or high density remnants within the volcanic channels during Miocene-Pliocene,whereas the low-velocity zone of western Tengchong reveals the magmatic and heat flow activities from Pleistocene to present day.A strong lateral heterogeneity is observed in the crust structure of the Longling M>7 earthquake area.The occurrence of the M7.3 and M7.4 earthquakes are related to the structural variation across the Nu River fault and the Longling fault,both of which are located near velocity boundaries.The upper crust east of the Nu River fault and west of the Longling fault is characterized by high velocities,which is considered as a primary location for stress accumulation in the earthquake area;however,low velocities are observed in the region between the Nu River fault and the Longling fault.It implies that multiple magma intrusions probably decreased the rheologic strength in the crust.It is the distinct variation in the structure that made the Nu River fault and the Longling fault easy to produce seismic ruptures for the intense earthquakes under the effect of tectonic stress.We infer that these two earthquakes occurred at 10～12 km depth.
引文
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[16] Xu Y,Liu J H,Liu F T,et al.Crust and upper mantle structure of the Ailao Shan-Red River fault zone and adjacent regions.Science in China (Ser.D),2005,48(2) :156-164
[17] Zhao D P.Seismic images under 60 hotspots:Search for mantle plumes.Gondzvana Research ,2007,12(4) :335-355
[18] Lei J S,Zhao D P,Su Y J.Insight into the origin of the Tengchong intraplate volcano and seismotectonics in southwest China from local and teleseismic data.J.Geophys.Res.,2009,114:B05302,DOI:10． 1029/2008JB005881
[19] Liang C T,Song X D,Huang J L.Tomographic inversion of Pn travel times in China.J.Geophys.Res.,2004,109:B11304,DOI:10． 1029/2003JB002789
[20] Bassin C,Laske G,Masters G.The current limits of resolution for surface wave tomography in North America.EOS Trans.AGU,2000,81:F897
[21] Zhao D P,Hasegawa A,Horiuchi S.Tomographic imaging of P and S wave velocity structure beneath northeastern Japan.J.Geophys.Res.,1992,97(B13) :19909～19928
[22] Koketsu K,Sekine S.Pseudo-bending method for three-dimensional seismic ray tracing in a spherical earth with discontinuities.Geophys.J.Int.,1998,132(2) :339～346
[23] Paige C C,Saunders M A.LSQR:An algorithm for sparse linear equations and sparse least squares.ACM Trans.Math.Softw.,1982,8(1) :43～71
[24] 赵慈平,冉华,陈坤华.由相对地热梯度推断的腾冲火山区现存岩浆囊.岩石学报,2006,22(6) :1517～1528 Zhao C P,Ran H,Chen K H.Present-day magma chambers in Tengchong volcano area inferred from relative geothermal gradient.Acta Petrologica Sinica (in Chinese),2006,22 (6) :1517-1528
[25] Lees J M.Seismic tomography of magmatic systems.J.Volcanol.Geotherm.Res.,2007,167(1-4) .37～56
[26] Monteiller V,Got J L,Virieux J,et al.An efficient algorithm for double-difference tomography and location in heterogeneous media,with an application to the Kilauea volcano.J.Geophys.Res.,2005,110:B12306,DOI:10． 1029/2004JB003466
[27] Park J,Morgan J K,Zelt C A,et al.Volcano-tectonic implications of 3-D velocity structures derived from joint active and passive source tomography of the island of Hawaii.J.Geophys.Res.,2009,114(B9) :B09301,DOI:10． 1029/2008JB005929
[28] Sherburn S,White R S,Chadwick M.Three-dimensional tomographic imaging of the Taranaki volcanoes,New Zealand.Geophys.J.Int.,2006,166(2) :957～969
[29] Waite G P,Moran S C.V? Structure of Mount St.Helens,Washington,USA,imaged with local earthquake tomography.J.Volcanol.Geotherm.Res.,2009,182(1-2) :113～122
[30] Molina I,Kumagai H,Le Pennec J L,et al.Three-dimensional P-wave velocity structure of Tungurahua Volcano,Ecuador.J.Volcanol.Geotherm.Res.,2005,147(1-2) :144～156
[31] De Luca G,Filippi L,Patane G,et al.Three-dimensional velocity structure and seismicity of Mt.Etna volcano,Italy.J.Volcanol.Geotherm.Res.,1997,79(1-2) :123～138
[32] De Natale G,Troise C,Trigila R,et al.Seismicity and 3-D substructure at Somma-Vesuvius volcano:evidence for magma quenching.Earth Planet.Sci.Lett.,2004,221(1-4) :181~196
[33] 皇甫岗,姜朝松主编.腾冲火山研究.昆明:云南科技出版社,2000． 46～57 Huangfu G,Jiang C S.Study on Tengehong Volcanic Activity (in Chinese).Kunming:Yunnan Science and Technology Press,2000． 46～57
[34] Harvard Centroid Moment Tensor Catalog,http://www.globalcmt.org/CMTsearch.html (last accessed Oct.2010)
[35] 张忠杰,白志明,王椿镛等.三江地区地壳结构及动力学意义:云南遮放-宾川地震反射/折射剖面的启示.中国科学(D辑),2005,35(4) :314～319 Zhang Z J,Bai Z M,Wang C Y,et al.The crustal structure under Sanjiang and its dynamic implications:Revealed by seismic reflection/refraction profile between Zhefang and Binchuan,Yunnan.Science in China (Ser.D) (in Chinese),2005,35(4) :314～319
[2] Wang Y,Zhang X M,Jiang C S,et al.Tectonic controls on the late Miocene-Holocene volcanic eruptions of the Tengchong volcanic field along the southeastern margin of the Tibetan plateau.J.Asian Earth Sci.,2007,30(2) :375~389
[3] 李大明,李齐,陈文寄.腾冲火山区上新世以来的火山活动,岩石学报,2000,16(3) :362～370 Li D M,Li Q,Chen W J.Volcanic activities in the Tengchong volcano area since Pliocene.Acta Petrologica Sinica (in Chinese),16(3) :362～370
[4] Shangguan Z G,Zhao C P,Li H Z,et al.Evolution of hydrothermal explosions at Rehai geothermal field,Tengchong volcanic region,China.Geothermics,2005,34(4) :518～526
[5] Chen F,Satir M,Ji L,et al.Nd-Sr-Pb isotopes of Tengchong Cenozoic volcanic rocks from western Yunnan,China:evidence for an enriched-mantle source.].Asian Earth Sci.,2002,21(1) :39～45
[6] 周真恒,向才英,邓万明.云南岩石圈热结构.中国地震,1997,13(3) :213～223
[7] Bai D H,Meju M A,Liao Z J.Magnetotelluric images of deep crustal structure of the Rehai geothermal field near Tengchong,Southern China.Geophys.J.Int.,2001,147(3) :677～687
[8] 胡家富,丛连理,苏有锦等.云南及周边地区Ig尾波Q值的分布特征.地球物理学报,2003,46(6) :809～813 Hu J F,Cong L L,Su Y J,et al.Distribution characteristics of Q value of the Lg coda in Yunnan and its adjacent regions.Chinese J.Geophys.(in Chinese),2003,46(6) :809～813
[9] Wang C Y,Gang H F.Crustal structure in Tengchong Volcano-Geothermal Area,western Yunnan,China.Tectonophysics,2004,380(1-2) :69～87
[10] 楼海,王椿镛,皇甫岗等.云南腾冲火山区上部地壳三维地震速度层析成像.地震学报,2002,24(3) :243～251 Lou H,Wang C Y,Huangfu G,et al.Three-demensional seismic velocity tomography of the upper crust in Tengchong volcanic area,Yunan province.Acta Seismol.Sinica (in Chinese),2002,24(3) :243～251
[11] 高 星,郭志,王卫民等.用转换函数方法研究腾冲-临沧地区地壳结构.地球物理学报,2008,51(2) :451～459 Gao X,Guo Z,Wang W M,et al.Crust structure beneath Tengchong Lincang region,Yunnan province,revealed by transform function.Chinese J.Geophys.(in Chinese),2008,51(2) :451～459
[12] 贺传松,王椿镛,吴建平.腾冲火山区S波速度结构接收函 数反演.地震学报,2004,26(1) :11～18 He C S,Wang C Y,Wu J P.S-wave velocity structure inferred from receiver function inversion in Tengchong volcanic area.Acta Seismologica Sinica (in Chinese),2004,26(1) :11～18
[13] 秦嘉政,皇甫岗,李 强等.腾冲火山及邻区速度结构的三维层析成象.地震研究,2000,23(2) :157～165 Qin J Z,Huangfu G,Li Q,et al.3-D chromatography of velocity structure in Tengchong volcano areas and nearby.J.Seismol.Res.(in Chinese),2000,23(2) :157～165
[14] Huang J L,Zhao D P,Zheng S H.Lithospheric structure and its relationship to seismic and volcanic activity in southwest China./.Geophys.Res.,2002,107 (B10) :2255,DOI:10． 1029/2000JB000137
[15] Wang C Y,Chan W W,Mooney W D.Three-dimensional velocity structure of crust and upper mantle in southwestern China and its tectonic implications./.Geophys.Res.,2003,108(B9) :2442,DOI:10． 1029/2002JB001973
[16] Xu Y,Liu J H,Liu F T,et al.Crust and upper mantle structure of the Ailao Shan-Red River fault zone and adjacent regions.Science in China (Ser.D),2005,48(2) :156-164
[17] Zhao D P.Seismic images under 60 hotspots:Search for mantle plumes.Gondzvana Research ,2007,12(4) :335-355
[18] Lei J S,Zhao D P,Su Y J.Insight into the origin of the Tengchong intraplate volcano and seismotectonics in southwest China from local and teleseismic data.J.Geophys.Res.,2009,114:B05302,DOI:10． 1029/2008JB005881
[19] Liang C T,Song X D,Huang J L.Tomographic inversion of Pn travel times in China.J.Geophys.Res.,2004,109:B11304,DOI:10． 1029/2003JB002789
[20] Bassin C,Laske G,Masters G.The current limits of resolution for surface wave tomography in North America.EOS Trans.AGU,2000,81:F897
[21] Zhao D P,Hasegawa A,Horiuchi S.Tomographic imaging of P and S wave velocity structure beneath northeastern Japan.J.Geophys.Res.,1992,97(B13) :19909～19928
[22] Koketsu K,Sekine S.Pseudo-bending method for three-dimensional seismic ray tracing in a spherical earth with discontinuities.Geophys.J.Int.,1998,132(2) :339～346
[23] Paige C C,Saunders M A.LSQR:An algorithm for sparse linear equations and sparse least squares.ACM Trans.Math.Softw.,1982,8(1) :43～71
[24] 赵慈平,冉华,陈坤华.由相对地热梯度推断的腾冲火山区现存岩浆囊.岩石学报,2006,22(6) :1517～1528 Zhao C P,Ran H,Chen K H.Present-day magma chambers in Tengchong volcano area inferred from relative geothermal gradient.Acta Petrologica Sinica (in Chinese),2006,22 (6) :1517-1528
[25] Lees J M.Seismic tomography of magmatic systems.J.Volcanol.Geotherm.Res.,2007,167(1-4) .37～56
[26] Monteiller V,Got J L,Virieux J,et al.An efficient algorithm for double-difference tomography and location in heterogeneous media,with an application to the Kilauea volcano.J.Geophys.Res.,2005,110:B12306,DOI:10． 1029/2004JB003466
[27] Park J,Morgan J K,Zelt C A,et al.Volcano-tectonic implications of 3-D velocity structures derived from joint active and passive source tomography of the island of Hawaii.J.Geophys.Res.,2009,114(B9) :B09301,DOI:10． 1029/2008JB005929
[28] Sherburn S,White R S,Chadwick M.Three-dimensional tomographic imaging of the Taranaki volcanoes,New Zealand.Geophys.J.Int.,2006,166(2) :957～969
[29] Waite G P,Moran S C.V? Structure of Mount St.Helens,Washington,USA,imaged with local earthquake tomography.J.Volcanol.Geotherm.Res.,2009,182(1-2) :113～122
[30] Molina I,Kumagai H,Le Pennec J L,et al.Three-dimensional P-wave velocity structure of Tungurahua Volcano,Ecuador.J.Volcanol.Geotherm.Res.,2005,147(1-2) :144～156
[31] De Luca G,Filippi L,Patane G,et al.Three-dimensional velocity structure and seismicity of Mt.Etna volcano,Italy.J.Volcanol.Geotherm.Res.,1997,79(1-2) :123～138
[32] De Natale G,Troise C,Trigila R,et al.Seismicity and 3-D substructure at Somma-Vesuvius volcano:evidence for magma quenching.Earth Planet.Sci.Lett.,2004,221(1-4) :181~196
[33] 皇甫岗,姜朝松主编.腾冲火山研究.昆明:云南科技出版社,2000． 46～57 Huangfu G,Jiang C S.Study on Tengehong Volcanic Activity (in Chinese).Kunming:Yunnan Science and Technology Press,2000． 46～57
[34] Harvard Centroid Moment Tensor Catalog,http://www.globalcmt.org/CMTsearch.html (last accessed Oct.2010)
[35] 张忠杰,白志明,王椿镛等.三江地区地壳结构及动力学意义:云南遮放-宾川地震反射/折射剖面的启示.中国科学(D辑),2005,35(4) :314～319 Zhang Z J,Bai Z M,Wang C Y,et al.The crustal structure under Sanjiang and its dynamic implications:Revealed by seismic reflection/refraction profile between Zhefang and Binchuan,Yunnan.Science in China (Ser.D) (in Chinese),2005,35(4) :314～319
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